Mod #82: Air Conditioner Hard Start Capacitor

Mod #82: Air Conditioner Hard Start Capacitor

Submitted on: 05/27/09

     Category: cooling, featured
Mod Rating: 12345

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Mod Description:

Ever try to start your A/C on a hot day at high altitude with a generator that is supposedly rated to handle the A/C’s starting requirements? The generator struggles, goes in to overload, or just plain stalls because it cannot supply the current demands of the A/C’s motor fast enough. Stories abound that many are able to start their RV air conditioners using a Honda EU2000 or Yamaha 2400i, or other small wattage generator. How are they able to do this while others can’t? Chances are they have modded their RV’s air conditioner with a hard start capacitor.

Mod Difficulty:

A typical RV air conditioner will have both a compressor motor starting capacitor and blower motor run capacitor, since they are generally of the Capacitor Start Induction Run (CSIR) type. The other less common type is the Permanent Split Capacitor (PSC) arrangement, which is not usually used in an RV application. Even if your A/C has a starting capacitor, you can still benefit from this mod. Most stock starting capacitors are a bit undersized and replacing it with a larger boost capacitor can help, especially if you are trying to start your A/C using a small generator. For those whose A/C has no starting capacitor from the factory, this mod will really help with compressor motor startup current demands.

The recommended (and most popular) starting capacitor for a 13,500-15,000 BTU RV A/C is the Supco SPP6E boost capacitor. This capacitor has an electronic disconnect and provides about twice the current boosting power as the factory start capacitor. If your A/C doesn’t have a seperate boost capacitor as shown in the pictures above, it’s likely that the run capacitor doubles as the boost capacitor, and also has a Positive Temperature Coefficient Relay (PTCR), a fancy term for the way the capacitor is removed from the circuit once the motor starts. The PTCR is prone to failure which can cause the capacitor to fail, and thus make the compresor motor startup current demands very high or not able start at all. This is the reason Supco makes an electronic version of the PTCR. It is much more reliable and is integrated in to the capacitor packaging.

So now that you know more than you ever wanted to know about starting capacitors, how do you mod your RV with one? It’s actually pretty easy. The hardest part is getting on the roof of your RV. To install the capacitor, you must remove the shroud covering the A/C internals. But first, be sure to disconnect any electrical power from the RV. You will be working with AC wiring which, if energized, can kill you. If in doubt, consult a qualified electrician to either assist or do the job for you. Don’t try this mod if you are unsure!

Start by removing the A/C cover. These are typically secured with many screws so use a battery-powered screw gun unless you prefer a hand workout. Locate the utility box containing the motor and/or starting capacitor. On a Dometic brand A/C, it’s located near the top right corner and should have a wiring diagram on the outside of it. Remove the screws holding the cover on, then remove the cover. There should be two screws (refer to the pictures above).

After the cover is removed, you should see either one or two cylindrical looking parts with several wires running to them. If there are two, then the one that is usually black and totally round (not oval-shaped which is the blower motor run capacitor) is the factory starting capacitor. it should have two wires coming from it. If this is the case, simply disconnect the wires leading from the starting capacitor and remove it. The Supco capacitor will be a direct replacement. Connect the two wires from the new capacitor to where the old capacitor wiring was connected.

If your A/C does not have a starting capacitor, refer to the Supco wiring recommendations that came with your boost capacitor for the various types of capacitor/wiring configurations. Generally though, the new boost capacitor will be wired in parallel, or “piggy-back”, to the motor run capacitor using the supplied jumper terminals. Again, if in doubt, seek the advice of a professional electrican or HVAC technician.

You thought there was more to this mod? Nope. It’s really that simple to do. Not only will your A/C start up easier while on shore power without popping the breaker, you stand a much better chance of starting and running the A/C using a smaller generator. If you have questions, feel free to comment below and we will do our best to get you an answer quickly!

TipIf you are testing out your new boost capacitor, be sure you allow several minutes between startups of your A/C. This ensures that pressures within the A/C system equalize and the compressor motor will start much easier. If it’s particulary hot out, the A/C system will have very high pressure on one side of the system after shutdown. You may have to wait as long as 5 minutes before cycling the A/C.
TipBefore touching any of the wiring connected to startup or motor run capacitors, you should discharge them. Capacitors are electricity storing devices and can provide a nasty shock if it is you that provides the discharge path. You can discharge a capacitor by shorting it’s terminals. Some do this by placing a screwdriver blade across the terminals. While this works, you may arc the screwdriver to the terminals, making it difficult to remove the screwdriver. Another way is to use a high-wattage resistor to short the terminals. You can find one of these at your local electronics store.

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189 Comments For This Mod

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  1. Bob Vaughn

    I had to have a hard start capacitor installed on my AC at home….

  2. Luke Scholl

    Will a Supco SPP6 work for this application or do you recommend the SPP6E only?

  3. ModMyRV

    @Luke: The differences between the SPP6 and the SPP6E are that the SPP6E is the electronic version. It uses an electronic potential relay rather than the thermo-type PTC found on some older A/Cs. It also has a backup electronic timing circuit to protect the compressor as well as voltage sensing circuitry. And there is also an instant re-start capability. The SPP6 doesn’t have these features.

    For the few extra dollars, the “E” version is worth it. If you already have the SPP6, you should still gain the benefits of a hard start capacitor, just not all that are available.

  4. Brad Kahler

    Where can I purchase the SPP6E capacitor ?

  5. ModMyRV

    Try here:

  6. John Weber

    Can the Honda2000i generator be isolated to run only the generator? I am thinking I want a separate plug for the generator running directly to the AC unit, with the circuit breaker cut off. My goal is to let my solar battery system run the rest of the rig and the generator run the AC. Is this possible?

  7. ModMyRV

    @John Weber - What size solar system and batteries do you have? When you say “run the rest of the rig”, what are you running?

    What you are asking to do is possible either by using a transfer switch inbetween the A/C’s breaker and the generator, or by disconnecting the wiring from the breaker panel and adding an extension and plug to the wiring. This would plug directly in to the generator.

  8. John Weber

    My solar system consists of four 100 watt panels and six 6-Volt batteries with a solar boster and a 2000 watt Inverter. I can’t run my air conditioning from the solar system because it really doesn’t have the power but I usually can run everything else in our rig ( a Montana 5th Wheel 3075) which would include lights, microwave, fans, tv and radio. Since we like to boondock occasionally I wanted to be able to add on the air conditioner as an item I could run, but I am willing to try to isolate it and run it with just my Honda generator (E2000i). Since we would want to use hook-ups if at a campground it sounds like the transfer switch would work best. Can you recommend one?

  9. Steve Carson

    This is great info. I have a coleman air conditioner and am needing to install a hard start. My model # is 8335-896 ( it is a 15,000 btu). Will any hard start kit work? Where can I purchase one of these. All the rv places around are out of them. Thanks and great article.

  10. ModMyRV

    @Steve Carson: Most any hard start capacitor for and RV A/C unit will work as the capacitance range is suitable for motors powering 11,000 to 15,000 BTU units. But I would be sure the one you buy is correct for your A/C model. Here is a link to where I bought mine and I installed it on my 13,500 BTU Dometic A/C unit:

    You can also go to Supco’s site and look at what’s available. They also have links to distributors and dealers too.

  11. ModMyRV

    @John Weber: Looks like your 5er has 50 amp service. If so, have a look at these transfer switches:

    You may be able to get away with using a smaller capacity switch if all you are powering is the A/C. In this case, you can use the 30 amp model in the link above. A bit cheaper and smaller in size too.

  12. John Weber

    I want to add in a Transfer Switch and wiring for my generator to plug in to the rig using a separate line just for the Air Conditioner. How do I determine which is the correct wire for the Air Conditioner when I am at the main breaker panel. I know how to locate the Hot wire at the breaker but how do identify the neutral wire?

  13. plascell

    I wasn’t having a problem with my EU3000is, but the A/C being 7 years old, I thought I would help it anyway I could. First asked a friend to try his EU2000i to run my A/C. It would start and run OK. If shut off for a half minute and then restarted, it didn’t with the high compressor head pressure. It would overload the EU2000i at about 3800-4000 watts and trip. I installed the SPP6E after removing original start cap (43-52 mfd). And tried again with the EU2000i. It started OK the first time, but again overloaded trying to restart. Next, with EU2000i idling in economy mode, and the A/C being off for 3 minutes, it would start OK and run. The magic appears that the EU2000i will operate the 15,000 BTU A/C, but when the thermostat shuts it off after reaching the set temperature, it needs to stay off for a few minute minutes before restarting, or else the head pressure is too great and it overloads the EU2000i generator. It is nice that it will start from the ECONO mode because when it is running it draws about 1000 watts and the generator will run slower than full speed. The battery charger, refrigerator, and electric water heater were disabled for these tests.

  14. Bob Pierce

    I did this mod today. The Supco is quite a bit larger than the start capacitor that was there so I had to mount it alittle differently. It started right up. I ran out of daylight so I will have to do further tests tomorrow. So far…it’s good……

  15. Capn_Silver

    Something I have found out is that any generator with the “i” after the wattage (e.g., 2000i) means that it has an inverter built in. This means that if you are attempting to start something that takes a large surge to start (air conditioner, air compressor, etc) you may not be able to do so. I have a Sears 1.5hp air compressor that cannot be started with a Kipor 2000i generator, but will start with a Craftsman 1200watt standard generator. I took my generator to a Kipor repair station and the tech attached the air compressor to a Kipor 3000i to it and it still did not have the “oooomph” to run the compressor. Just something to look out for in today’s modern age.

  16. Adam-12

    Great mod instructions here. One thing I noticed about the article was the fact it mentions only ONE Honda EU2000i generator trying to start an a/c unit. Would TWO parallel Hondas work for a 15K BTU RV a/c on a hot day or at an altitude of about 4,500 feet MSL or less?

    Thank you.

  17. C Collins

    Bought the capacitor, went to put it on, and found out that the “guts” of my AC unit don’t look like the pictures above. Can someone please tell me how to tell if I have a CSIR type or a PSC type AC unit? I can’t make heads or tails of the wiring diagram, and I have two silver cylinders. One is round and larger, the other is oval and small. One has 4 wires and the other has two, but they don’t look like they are connected together like in the pictures. The wires from both lead to the compressor. Thanks for any help.

  18. ModMyRV

    @Adam-12: 2 EU2000i generators should have little trouble starting a 15K BTU A/C at that altitude. You might have to turn off the eco-throttle though. When I had my 2 EU2000 gennys, I had trouble starting a 13.5K Coleman A/C at 4700 feet. I discovered the A/C didn’t have a hard-start cap. I put one on and I was able to start the A/C with the eco-throttle on. At 7000 ft. however, I had to turn off the eco-throttle.

  19. ModMyRV

    @C Collins: In general, the oval shaped cylinder is the motor run cap and the round cyclinder is the motor start cap. Keep in mind that the pictures above are for a 2007 Dometic 13.5K BTU A/C unit. Your A/C may be entirely different.

    What model is your A/C? Do you have any pictures? You could post the link to the pics here in a comment making it much easier to see what you are dealing with.

    If posting a pic isn’t possible, I would recommend you have someone who understands your wiring diagram assist you with the installation.

  20. Erwin

    Has anyone noticed the SPP6 and the SPP6E are rated total different? The SPP6 is rated from 90-277 volts and the “E” is rated from 177-277 volts. It looks like the “E” version will not work on the typ 110 volt RV airconditioner. One supplyer even comes out and states this. Looking at the spec’s the SPP4E is spec’d for 90-133 volts, and is the same size cap as the 6E and should work?

  21. gaweber

    I tried this mod with a SPP6E and did not see much improvement still won’t start my Brisk Air 11,000 BTU Air conditioner with my 2500 Watt generator (inverter type). Any thoughts why it did not work? or what else I can try.

  22. Erwin

    Note the comments above. The Supco “E” version, per their spec, sheet is not rated for use on 110 volt units. The none E is version is. It probably is not is not working? Try a SPP6 and let us know how it works?

  23. gaweber

    The info on Supco’s web site says the SPP6E is for 177V to 277V applications but the working voltage is 90V to 277V. so I believe the SPP6E was ok to use. the SPP4E might be cheaper but is not rated for the HP of my compressor.

    Here is Supco’s info

  24. Erwin

    I finally got the SPP4E and put it on my 13.5K BTU RVP roof air. The air now starts from my YF2800 Yam generator in ECONO mode with only a slight hickup. Note - talked to the supco tech guy. he says folks use the 6E on 110 volt airs but results are “ify” as you found out.

    Check out pages 3 and 123-124 of Supco spec sheets

  25. lavelle pierce

    i have a coleman roof ac model 6757-707-716, i installed a cap that goes to motor and still will not start when i un hook the brown wire it will blow high , when i plug it back it will staet slow again thanks

  26. 73GMCer

    The mod worked great and saved my marriage (she still thinks I am smart on my own). My Duotherm 15K had different (Male vs.Female) connectors - I installed new ones but twist ties would have worked. Instructions on the SPP6E said to us it in parallel; it worked that way but there was no room for both and fearing the original was defective or that unneeded capacitance might be too much for the compressor, I eventually followed the modmyrv directions. Two days later I was answering inquiries and directing people to this site. Thanks. Doug

  27. 73GMCer

    Has anyone successfully used a 2K generator with this mod? A friend wants to know.

  28. wmarsha

    okay, I am upgrading my 85 airstream with a new carrier airv low profile 15k btu a/c. I am planning on powering this with a honda eu3000. I have the spp6e unit in hand and have the a/c unit ready to go up on the roof. I would like to mount/connect the new capacitor now, before the unit is on the roof (duh!) I do want to be sure i connect this to the correct point in the factory wiring and i want to be sure this unit will need this mod. Okay, there are my questions. the wiring schematic shows the comp cap with a ptc wired in. the factory cap has 3 poles; labelled F, C ,H, with the comp wires going to C, H. The PTC also connects on the same poles. Is this where I attach? and do I need to disconnect anything?

  29. Kevin Mcnulty

    I will try the spp6, but does anyone know if these alternatives might also work or help.

    Starting the AC on house current and then switching plugs quickly to the 2000i watt genereator

    or disengage the fan motor 2.5 amps and run it off batteries
    reducing the load from 16.5 to 14 (compressor alone). Starting the compressor alone with the 2000i genny and then adding the motor fan back into the genny after the compressor is running smoothly

    or using premium gas (91 octane)

  30. Dennis

    I just installed one of these in my DuoTherm 13.5k btu.. Its an older model from 1989 (works great on the built-in genny or shore power). I have a new Honda EU2000i which I wanted to run the air off of instead of cranking up the Onan Emerald 1 4000 generator. I took the old capacitor out as instructed above and put the new one in. Hooked the power cord back up thats runnign from my house and left sit for a bit. Then plugged the rig into my Honda, put it on full rather than econo mode. Tried to start the AC but threw the overload on the Honda.. :( Do you think mine is too old for this to work? Would it help if I connected both the old one and the new one?

  31. ModMyRV

    @Dennis: You may want to measure the A/C’s start-up current demand with a simple ammeter. Having an older compressor motor might just put it out of the realm of the EU2000. Also, are you at sea level? What size power cord are you using and how long is it? Are all of the other AC circuits switched off in the RV? The EU2000 needs all the help it can get in this case so be sure no other loads are consuming power when starting the A/C.

  32. TTaddiction

    I was actually on my way to upgrade to the Yamaha EF3000iSE or 2nd 2400 gen., when I read this Mod.
    Ordered the SPP6E for my ‘03 rockwood’s 13.5btu AC. My Yamaha EF2400iSE, starts the AC but then the AC shuts down, no other devices were energized in the trailer, refrig was on gas mode. I’m hoping this will help. It will save $$ on upgrading the Yamaha. I’m heading up to 7,000′ elev soon and wonder how it will do at that elev?(not that I’ll need AC there). New to the RV club but lovin it.

  33. Dave M

    First of all the Duo Therm air conditioners in the range of 11KW to 15KW are generally 110 volts. Now with that said, the Mod as discussed references 13.5 to 15 K BTU duo therm air conditioners, and recommends a replacement of the start capacitor. My question is: Has anyone used the recommended start capacitor SPP6E on a 11 K Duo Therm, even though the Operating voltage is shown as 170-277. I am somewhat confused as it seems that at least one poster tried the 6E and it did not work and he went to the 4E. However at a minimum, a 11K produces approximately 1.5 Horse Power and this falls out of the range of the 4E. Has anyone had success with the 6E and 110 volts?

  34. ModMyRV

    @Dave M: Just a slight correction on your ranges. A/C outputs are measured in BTU (British Thermal Units), not KW (kilowatts). Guess I’m just a stickler for accuracy. ;)

    To answer your question: I have personally installed the 6E on a 13.5K BTU Duo Therm and did notice an increase in starting power, particularly at high altitudes. Yes, the voltage ranges are suspect and I’m having trouble getting a straight answer from Supco. They are “getting back to me” as the saying goes.

    The 4E is probably a little small for the typical RV A/C unit. However, it is possible to piggy-back a 4E on the stock cap if your A/C has one from the factory. Newer ones generally do.

    I have never tried this but theoretically it should work.

  35. riverlake

    I did this mod yesterday on a brand new travel trailer with a Coleman-Mach 15kw unit.

    Before the mod, my first trip out was to mountains about 6,700 feet altitude. I didn’t really need air conditioning but I tried running it with my Honda eu3000is without success. I tried again when I got back to 1,000 feet and ran it fine, even at reduced speed with the eco-throttle.

    My startup amps were 12.2 before the mod, after I put the start capacitor on I got 10.2 amps. I am looking forward to seeing if the 2 amps will be enough savings at higher altitudes for the EU3000.

    Since my unit was different than the one pictured, I just followed the wiring diagram on the inside of the electrical cover. It showed (as an option, in dotted line) a start capacitor piggy-backed onto the compressor run capacitor. There were even unused blade connectors to connect to.

    Thanks for this mod. Next is the Ultra-Fab electric levelers!

  36. Dusty

    Just a couple of comments to sort out the electrical facts.
    1- running amps are not the problem, starting surge is. The hard start kit should do little to change running amps and the dif from 10.2 to 12 may just be how hot the day is.
    2 - the hard starts with the “E” have an electronic timer etc inside to do the work. The 4E and 6E are the same 80 micro farads capacitor. The electronics are rated for dif voltages.
    3 - With the 6E rated 170-270 volts and 4E rated 90-133. The major HP rating difference is caused by 110 versus 220 volt operation. In simple terms the 220 volt motor can be rated for about double the 110 V for the same current.

    Operation of a 6E on 110 volts is iffy, ask the vendor. If you want to use a 6 on 110 V unit try the non E, it’s rated 90-270 volts.

  37. mlbeep

    I just tried this exactly as posted.
    I am NOT an electrician, not even close…
    I have a 2010 Dutchman Denali 292RKX-DSL with an optional 15K A/C.
    I switched out the original relay (a CSC unit marked 10.0uf +/-6% 370VAC/B) with a Supco SPP6E. VERY easy swap, only changed out the connections on the Supco with male flat terminals to mate with the A/C unit.
    Returned power and the A/C fired right up, but noticed it was running about 1/2 speed. Changed it to high-speed, and still sounded really slow.
    I swapped back to the original relay.
    On the back of the Supco unit is says (in red) “SPP6E Recommended for 1/2 to 3 h.p. 170-277V 88-106 mF”
    The SPP4E is 90-130V but only recommended for 1/8 to 1h.p.

    I don’t even have a generator yet, but am contemplating the 3000w Honda (EU3000iHAN). Am I wasting my time and money on this relay idea? Paid (wasted) $57.00 on this one…

  38. ModMyRV

    @mlbeep: when you swapped back to the original, did the motor “slowness” go back to normal? This is interesting in that the cap is only used to help start the motor. After the motor is started, the cap is removed from the circuit electronically (that’s the “E” on the end of the cap number). The only thing I can think of is that you may have swapped out the motor run cap. Doing that could result in the problem you are having. Do you have any pictures of your install?

  39. mlbeep

    Swapping back returned the run to normal. I thought this was really odd but glad things returned to normal.
    There were two items in the “box” under the hood of the A/C, the smaller one had two connections on top, that is what I swapped. The much larger one had a bunch of connections on top…I didn’t mess with that one. The smaller unit also says “SH P2 Capacitor EIA-458-A” on it. The A/C is a 15k Duo Therm unit. Now that I looked at the pictures above again, mine is identical…except my starter cap is silver and short but fat, barely fits in the box, not small and black. That one is dated ‘05, mine is ‘09. I don’t have pictures…but will take some…how do I post/send them? THANKS for your assistance!

  40. ModMyRV

    The best way to post pictures would be in the forum. Start a new thread and we’ll try and get some answers for you.

  41. mlbeep

    OK, done did it.

  42. Kevin Mcnulty

    I tried the spp6 but It’s not enough of a kick to run off a 2000 watt honeywell 2000i. I didn’t want to spend 2 to 3 thousand dollars for the honda 3000 or tandum honda 2000’s. so I bought another Honywell 2000i, they are only $299 at home depot. Unfortunaly the honeywell generators can not be run in parallel like the honda’s. So I seperated the fan motor from the condenser. Now each one has its own generator. It required buyng another run capacitor for the new motor circuit. First I turn the generaror on, plug the fan in first to #1 the plug the condenser into #2 with the circuit breaker off, by teasing the circuit breaker once or twice, I get the RPM high enough to run the condenser. I also leave it in full coldest setting so it dosent cycle off.

  43. Lloyd Coltman

    I have an old Duo-Therm ‘Sunchaser’ 13,000btu A/C that did not come with a compressor start capacitor. Having read some of the replies in this file, I’m a little confused. On this A/C, would you recommend the SPP6, SPP6E, or SPP4E? Note: the compressor run current on this unit is listed as the same as the 57915.621 (11A), so the HP is ~1.4

  44. Kevin Mcnulty

    Lloyd , you will need a way to control the start capacitor, since you don’t have one you should get the SPP6E with the built in electronic controls

  45. Lloyd BC

    Well, today I experimented with my A/C. I opened up my spare unit, removed the PTCR and start capacitor (25-30Mfd), and put them in my old 13,000btu ‘Sunchaser’. It then started not too bad with my Yamaha EF2400iSC, so as an experiment, I replaced the start capacitor with a 65-76Mfd unit I had. What a difference! The compressor starts with barely a ‘hickup’ from the generator, even though the gen constantly runs in ‘Econo’ mode. One thing I noticed was that Dometic placed a ‘charge bleed’ resistor across the start capacitor, to drain the charge off.
    I can see where I will be doing at least three units this winter, to make it easier for all of us to run our A/C’s off our smaller generators. I mean, who wants to pay $2000-3000 for a Honda EU3000iHandi, when a Yamaha EF2400iSC, at $1200-1800, will do the job, and quieter too.

  46. EJS4029

    I’m not sure if the hard start capacitor will help my situation. My Kipor IG3000 starts my Coleman 13.5 AC but after a few minutes it shuts off. I have the RV plugged into the 30AMP twist lock plug with adapter….Should I try using an adapter that uses the 2 20AMP plugs on the Generator to a single 30AMP outlet ? Or won’t that help. Any ideas appreciated.


  47. Lloyd BC

    I have heard that some ‘Off-Brand’ generators have problems holding a heavy load. I tried my ‘Duo-Therm 13,000 on a Yamaha EF2800i. It did same as you’re experiencing (assuming it’s kicking out on overload). My Yamaha EF2400iSC wouldn’t even start it, however the 2400 would easily start my buddie’s A/C, and now that I’ve done close to the complete mod (Salvaged parts from another A/C, but only 2/3 the capacitance) I can run the A/C without trouble. I’m currently waiting to get the SPP6 that I bought on e-Bay (for about 1/2 list price, including shipping) so I can finish the complete mod, and the other unit will be complete again. When you investigate your A/C, you may find it’s like mine, NO start capacitor at all. I wouldn’t have believed what a difference there is. As for your choice of outlets, stick with the ‘TwistLock’, you’ll get all there is to have.

  48. jbgreen68

    Hello, new to this forum, but interested in this mod….

    So, there seems to be a debate as to the SPP6E (rated 170-277V) or the SPP4E (rated 90-130V) will work for 110V 13.5 AC units.

    Seems it works for some, but not others. Has the 6E worked for most 110V 13.5 units out there? We have a new 2010 Salem 27RBS w/ the 13.5 Duo Therm unit.

    Just checking on which to order (the SPP4E or the SPP6E)… :-)

  49. Lloyd BC

    Looking at all the posts on this, I opted for the SPP6 (on e-bay for $14 incl shipping) because it might not be quite so voltage critical. I probably could have also used an SPP4, or SPP4E but none were offered on e-Bay. Now I wait ’til I’m in Seattle and can pick it up. In the interim, I’m operating with something between a SPP5 and SPP6 (assuming capacitors are the same values in ‘E’ and ‘non-E’ versions), made up from spare parts. I can tell you, the difference is phenominal, when compared to no start capacitor.

  50. Steve A

    I have a 93 travel trailer with a 13,500 btu AC unit. My Yamaha 2400i generator would start the AC occasionally but not consistently. I did the mod with the SPP6 (not the E) and had zero improvement. Still won’t start consistently. Any suggestions?

  51. Lloyd BC

    Steve A…..I have a 93 travel trailer with a 13,500 btu AC
    Can you give me a model # for the A/C? Run currents for Duotherm 13,500’s run from 11.0 amp to 12,4 amp depending on model, and locked rotor currents are 50-59 amp (compressor only). Are you trying to restart the compressor immediately after it has shut down, or are you trying to start both fan and compressor at the same time? Is anything else running at the same time? Since I did my makeshift mod, my 2400 consistantly starts the compressor with hardly a ‘Hickup’, where a Yamaha 2800 wouldn’t start and run it before. The A/C is modded to run the fan continuous when switched on, the compressor cycles as required, and when running the generator for A/C, I lock the fridge on LPgas. I can even recharge my batteries , as long as I don’t try to run too much off them at the same time.
    We also have no problems with our niece’s 13,500 A/C on the 2400.
    I suspect the only difference between the 4E and 6E is that the components in the 6E will tolerate higher voltages ( 240 vs 120), and by virtue of that, higher HP. Once you get beyond 1HP, the compressors generally run on 240 Volts (Other than RV A/C, and few have 240V service). Consider the avg 15,000 unit, close to 1500 running watts (2HP). But, in most cases, a ‘home’ unit this big would be running on 240 Volts.

  52. jbgreen68

    At the Supco website, looks like these are their specs:

    Operating Equipment Recommended Capacitor
    Voltage Range Range
    SPP4E 90V – 130V 1/12 to 1 hp 1/8 hp to 1 hp 88 – 106µF
    SPP5E 90V – 277V 1/12 to 10 hp 1/3 hp to 2 hp 43 – 52 µF
    SPP6E 90V – 277V 1/12 to 10 hp 1/2 hp to 3 hp 88 – 106µF

    Looks like they are stating the operating range is 90v-277v.

  53. Steve A

    Lloyd BC, The shroud says Coleman but the data plate says Recreational Vehicle Products, Wichita KS. I cannot make out the model number on the plate but here are the items I can read from the data plate: Compressor LRA 63.5, Compressor RLA 11.8, Fan Motor Amps 3.4, Fan Motor 1/3 HP.
    When I am trying to start the AC, I turn off all the other breakers so only the AC is energized. I do notice that the cool air circulation fan always comes on as the AC compressor is trying to start but I don’t see a way to keep that load switched off as the compressor is starting. I am not trying to restart the AC immeadiately after it has been running, I let it rest for at least a few minutes after it shuts down. Thanks for your help.

  54. Lloyd BC

    Definitely ‘Coleman’. I’ll make an assumption that like my Duotherm, you have only one control and one fan speed. On my unit, a previous owner had added a switch (ty-wrapped to the intake grille) to operate the fan independent of the thermostat. I thought that looked like S**t, so I removed it and spliced the wires together. In both my trailers, the A/C power is spliced through a junction/switch box in the ceiling. I opened the hot side splice, and installed a common light switch. Now, to operate the A/C, I turn on the switch, (fan starts and runs continuous), then I adjust the thermostat to start and control the compressor. So now, my A/C operates like the later model Duotherms, except it’s single speed. You need to find a wiring diagram for your A/C, and see if this is feasible. It certainly lightens the ’start load’.

  55. jbgreen68

    Wow…. opened the ‘hood’ on my Dometic 13.5K BTU A/C unit today to do a little investigation and when I opened up the capacitor box, I was quite surprised to see that there was NO start cap at all! I have a diagram on the cover that looks like th one in this link:

    In the diagram, notice the asteric around the start cap “not used on some models” that relate to the dashed lines.

    I tried my Yamaha EF2400is to kick it off the A/C unit, and no go (no surprise there). I’ll be getting the SPP6E to see if that helps.

  56. Lloyd BC

    JBG: I can almost guarantee you will be pleasantly surprised. I could not start my A/C at all with the 2400, and even a 2800 could not get it up to speed before O/L’ing out. As I noted above, after doing a makeshift mod, the 2400 handles it effortlessly. I’m just waiting to get the proper part.

  57. Lloyd BC

    I find it interesting that one retailer of the Yamaha 2400 (Wise sales) says it will run most 13,500 A/C’s, while another (USA Light) says it won’t. I can say from experience that of three A/Cs we tried (all 13,000 or 13,500), two started and ran fine, while the third (a cheap, simple, single speed 13,000), would not. After modification, it also started and ran perfectly on the EF2400i.

  58. lttlfeller

    Great information! I want to share my experience with this mod as it worked great. I recently bought a new 5th wheel with a Coleman Mach-air 15,000 btu A/C and I have a Yamaha EF2400i generator. My generator would not start the A/C before installing the hard start kit. I used the Supco SPP6 (not the 6E) because that is all I found locally. When I opened my A/C I discovered it did not have a start capacitor. I connected the SPP6 to the run capacitor which was very simple. Now my EF2400i starts and runs the A/C with only moderate loading. It seems like the generator even runs the 15,000 btu A/C easier than it ran our old 13,500 btu A/C. I’m very pleased with this mod… thank you!

  59. rrawls

    We have a 2009 RV the main a/c will run great for about 6 hrs. then the compressor will come on and go right back off within seconds. The fan will run constant while compressor kicks on and off again. Will this system help us.

  60. chad jones

    Question , one is there a reason you can not just piggy back the new hard start cap with the factor cap ? and on the new hard start cap I got one wire is black and one white , not on my RV AC which by the way looks just like the one in this posting. one is white and one is red, So I hooked the white wire on the new hard start kit directly to the top of my compressor were that white wire was and the black to were the red was. tested AC and it worked fine, kind of sounded like it started better but can really tell at this point , Does this sound ok for the way I wired it. Ps I also have pictures that I could email

  61. Barry N.

    Hi all,
    I purchased a Boliy 3,000 watt (3,300 watts peak) generator with a 30 amp outlet on it. I have a 5th wheel rv and plan on powering the entire rv occasionally with the generator, including the 13,500 btu a/c.
    In preparation for this I also purchased a Supco SPP6E capacitor, after having read the recomendation on this site. I did this without first investigating which start capacitor was currently installed, assuming that this E series could do nothing but improve the ability to run the a/c off the generator.
    Yesterday I made the switch, but was a little confused over several things, as detailed here:
    a) The original start capacitor turned out to be a CGE 88-108 MFD, not a smaller one. Did I replace needlessly?
    b) There was no charge to dissipate from the old one. I had not run the a/c for several days. Will a capacitor lose it’s charge over time, or is it possible that the capacitor was defective?
    c) On top of the old capacitor there was a device installed that I assume was a positive temperature coefficient resistor(determined through research on internet)It is printed “WSX-SACM motor starter”
    I made the capacitor switch but did not re-install this device. Should I have kept it in the circuit with the new capacitor?
    Anyway, I tried out the a/c first on shore power and then finally on my new generator. The a/c runs beautifully, compressor seems to sound a little easier starting and is hardly making my generator work.
    My last question is, have I done everything above correctly, or should I have left well enough alone? especially with regards to the resistor that I have not re-installed.

    I would sure love some comments from you that are more knowledgeable about all this than I.

    Thanks in advance

  62. jbgreen68

    I installed the SPP6E and it works like a charm! No issues kicking off the A/C unit with my Yamaha 2400.

    Great advice all!

  63. EJS4029

    When I opened my Coleman 13.5 A/C I discovered it did not have a start capacitor. How do I connect the SPP6 to the run capacitor ?
    Does anyone have any pictures or a diagram ? Thanks.

  64. ModMyRV

    @EJS4029: Maybe this forum thread will help?

  65. myakkatt

    Has anyone installed the SPP6E on a Carrier AirV 13.5 A/c. I looked in my capacitor box and there does not appear to be a start Capacitor. The scehmatic does not show one, there is a PTC small device next to large Capacitor. I would assume I just connect to the Herm and Comm and find a location for the Supco since it will not fit in the Capacitor Box? Any help is appreciated, Thanks

  66. fireman_tom

    Do you have to re-attach the strap after instal of can it sit free?

  67. Erik

    I ordered an SPP6 for my upgrade but they sent me an HS6 and said it was the same thing. It appears alot bigger than the start capacitor that came on the A/C. Is it the same thing? Is the SPP6 alot larger than the original equipment? Also if I can’t install inside the metal electric box can the capacitor be exposed to the elements of weather as long as it is up and under the shroud?

  68. ModMyRV

    @Erik - The HS6 is a direct replacement for the SPP6 and connects in the same manner. While you might get away with having the capacitor just under the shroud, you should try and shield it in some way other than the big shroud. Maybe you could buy a plastic box, like a hobby box from Radio Shack, to hold the cap in and attach it to the other box containing the motor run cap?

  69. Erik

    Ok thanks for the response. I was concerned about the size of the HS6. It looks alot larger than the SPP6 in the photos. And it is definately larger than the original start capacitor. Thanks

  70. ModMyRV

    @Erik - Take a look at this PDF. It shows the HS6 cap and that it is a replacement for the SPP6. Here is the link:

  71. Erik

    Ok I just installed the SPP6 but my concern is the wires on the new capacator were both black, not white and red so I assume it doesn’t matter which is which?? I put one to ths C term and the other to the H term. Also the old capacitor had a small square item on one of the terminals just like your picture showed. I left it on the old capacitor and installed the SPP6 as is without that small square piece. As it is 30 degrees here I will not try it out for a while just looking to see if I installed correctly????

  72. ModMyRV

    @Erik - Did the cap come with any instructions? The way you installed it sounds like it should work just fine but I would make sure according to the instructions.

  73. Erik

    It did not come with any instructions. Just a picture that shows the start cap getting hooked piggy back on the run cap. I was just concerned if I hooked the right wire to the right terminal since they were of the same color. Maybe it doesn’t matter and that is why they are the same color. Also my other concern was the small square box that was on top of one of the terminals on the old start cap. I did not put it on my SPP6.

  74. ywgclarke

    The confusion about which capacitor to use is aggravated by the fact that the gent who wrote it talks about the SPP6E, but at the bottom of the article has a link going to that links to a SPP6. SUPCO specs say that the E series has an electronically controlled cut out to remove the capacitor from the circuit when it has “sensed” the unit has started. This sensing circuit is VOLTAGE sensing and not Current sensing according to there specs. It also states the recommended voltage is 170-277V, but then shows the Operating voltage as 90-277V. If you go to there E Class comparison page it states the voltage as 90-277V but the Capacitance as 88-106uF @ 250V for the SPP6E. I would suggest that a device that senses voltage and not current to remove it from the circuit should be used in the recommended range. In my opinion that makes this the wrong Cap. The SPP4E is rated as 90-130V and 88-106uF @ 110V, which in my opinion makes this the correct E type capacitor for this application.
    However the straight SPP6 capacitor at half the price has a voltage rating of from 90-277 volts and 88_106uF @ 110V and is not voltage sensing, but uses ta ceramic Positive Temperature Coefficient Relay (PTCR) which is the better technology than my original Cap had (as a separate pice called a WSX-7 motor starter which was a bi-metallic coil).
    For less money the SPP6 appears to solve the hard start/ low voltage issue, with a far less sensitive device that the E class capacitor….. just my opinion. ywgclarke.

  75. Larry Winget

    Need to replace our fan capacitor on or Coleman Roof top RV a/c. This solution comes as a 3rd try to fix a very unusual problem. A/C will run fine for a while and will satisfy and shut off,however, some times when it comes back on the fan runs backwards blowing the air out the top of the RV and not inside. We then have to turn off the a/c and wait several minutes and then it runs the correct direction. This game gets very old especially in the middle of a hot summer night. Have had the control board replaced and that did not fix the problem. Then was told the it was a low voltage problem with the park we were camping in causing the a/c to do weird things. However, we camped at a different park after that and had the same problem. We have found no repairman that have ever heard of this problem. Called Coleman directly and they suggest replacing the fan capacitor. We are going to try this ourselves. Is there any written instructions anywhere for this procedure? And do you suggest trying anything else?

  76. jdviaje

    Thanks a lot for this MOD. I researched a lot before buying my generator. I had three problems, size, weight and price. I own a trailer Laredo 29BHS 2010 and it is pulled by a ford expedition, so I didnt enough space and capability to handle a big generator. I was looking for the smallest generator capable to handle the AC (13.5 BTU) at sea level (I live close to Dallas) and the other appliances at higher alttitude.
    After a lot of research I decided that the best option was a yamaha 2400 or similar but it was too big and expensive. Next option was a generator that is sale in ebay and have some good reviews but it has not support other than the saleman. The last option for me was the HW 2000i. I didnt find anybody here saying it works with a 13.5 AC but I found some people saying so at amazon, so I decided to try it.
    I bougth it and the capacitor. When both arrived I tried the generator with my RV. The generator worked very good and it was easy to turn on. Everything worked except the AC. I turn everything off except the AC and still didnt work.
    Then i changed the capacitor (spp6E). I tried with just the AC on and It worked fine. Then I turn on the tv and some ligths and still worked. Then i turned the AC off and on again and the generator couldnt do it. I turned everything off again, reset the generator and this time the AC started.
    This is just perfect for me. Maybe is not absolutly confortable but it is just perfect for occasional use.
    I moved the propane tanks a little to the front and build a little bed for the generator and a gas tank.
    I used that at padre island national sea shore. I located the generator around 35 feet fron the trailer and over a little hill and the noise from the sea was louder than the generator.
    Thanks again for the tip.

  77. nedco

    Armstrong AC:My 1975 Airstream has an Armstrong AC, commercial design I am told. RV dealers say no parts available, want to sell new unit. My unit has worked well until recently, fan works but when thermostat calls for compressor, it throws the circuit breaker. Question: is the Supco capacitor SPP6E the best choice for this older unit? I have replaced the start relay and this made no improvement in the described condition. This unit when working is superior to current models and I want to keep it in operation.

  78. Owen

    I have a 1996 model 11,000 Dometic Penguin AC. It will start and run like a champ on ground power but when I try my 3600LP Onan, the gen set stumbles,nearly stalls completely, but the RPM’s come back up, the compressor which has never kicked in clicks off, the fan continues to run but no cool air. The same thing with my EU3000I Honda gen set. My question is: will the hard start kit #3311883.000 solve my problem?

  79. mrbjr

    Just completed this mod and it works! I have two Honda generators, a EU 3000IS and 2000IS. Has been running on the 2000 for a little over an hour so far. Granted it is only in the low 80’s.. AC is a 13.5 Dometic…


  80. Tom Goodrich

    Will this mod work on a Dometic 15K BTU Heat Pump? If so, will installing it void the factory/extended warranty?

  81. jfdrewett

    Great upgrade.
    Coleman Mach 15k. Used the SPP6. I can run the A/C on my Honda 2000.

    Will most likely run it on my Honda 3000 but it was cool to see it work on the 2000


    Holding tank gauge mod is next.

  82. George Broyles

    I have a 15K penguin Dometic a/c on my motor home. I have blown 3 starting capacitors on the 2 year old unit. I purchased a Supco SPPG6 to install but found out that my current start cap has 3 wires and the Supco has only two. how do i wire the Supco.

  83. paul b

    i have a duo therm 10,000 btu, # 53210-005… what model of hard start relay do i need to order.. thanks!!

  84. ModMyRV

    @paul b: The Supco SPP6 should work fine for your size A/C.

  85. Dru

    I have purchased these capacitors and have tried to run my ac units in my rv with a honda 3000is I cant get the ac units to run or the honda to quit going in to overload mode when i switch on one of the units. im not sure that i am wiring the capacitor in right.

  86. mikeintn

    Now I’ve read so much I’m confused. I have 2 A/C units in my motorhome a brand new 13.5K BTU Duo-Therm and a 15K BTU Duo-Therm unit that is a 1998 model. My generator is a 5500 watt Onan unit. I can get both running if I start one in low, then the other and after a minute I can turn both to high. I would like to put a hard start cap in my 15K unit or maybe even both units to help the start up but don’t know which one to get now. Thanks for the help.


  87. Joel Bennett

    I have a coleman 7300 series rooftop a/c in my 95 prowler, it will start and run then kick breaker, after setting, I reset breaker start agin, runs, kicks breaker, it will keep doing this, what do I look for? cercuit breaker replacement or istall a hard start unit?

  88. mikeintn

    I just put one SPP6 in each of my A/C units. I REPLACED the small capacitor in the Duo Therm 15,000 BTU unit and added the the cap to the Duo Therm 13,500 BTU unit (there was NO start cap). I have photos and will post later. I then ran both on high cool for 3 hours and every so often I would hear the generator change sounds, but that was about it! No grunting, no stalling, nothing! Worked for me. Your mileage may very, as-is no warranty, not responsible for yours not working, consult A/C professional if you have ANY questions, consult your doctor before taking any medications, side effects vary from person to person, save a fish boycott BP. Have a nice day!

  89. Brian

    I bought a SPP6 capacitor for my 13,500 BTU Dometic Duo Therm. Since it was a 2009 unit I expected it to already have a start cap, but no such luck.

    The wiring diagram is extremely similar to the one posted here, however it shows the start cap as “optional”.

    Both of the leads on my SPP6 are black. I connected it as the directions said, in parallel, one to the white side, and one to the red. “Connect the two wires from the SPP6 in parallel with the run capacitor (one wire each side) without removing any original wires”.

    I started the A/C on my 2600KW generator and it acted exactly like it did without the new capacitor, I was very disappointed. I had expected that there would be some kind of improvement.

    I waited a while and swapped the leads thinking perhaps I had them reversed, nope…

    There only appears to be voltage on the capacitor when the compressor is running. If just the fan is on or the thermostat is up high, there is no voltage on the leads.

    Any suggestions? Could the capacitor be bad?

  90. tyler

    hello i bought the super boost spp6 with the 2 wires coming off it and i went to install on my 13,500 carrier rv ac unit and found that the capacitor has all kinds of wires coming out of it and im not sure where to hook in my spp6 unit can anyone tell me how to hook my new capacitor up to my old one.

  91. daveinwa

    I have installed the SPP4E Supco hardstart cap in my AC unit. This one sized up for the unit on my 19′ trailer (based on compressor LRA rating). The Supco website will tell you which one is for your application. You should follow the instructions, and if you don’t understand something, consult an electrician or AC repair person before proceeding. Joel… You need to take an amp reading with a clamp meter to see if your compressor or fan is going bad. Yes, a start cap helps give the bump to start a compressor (which is really just a pump), but if you are tripping a breaker after it’s started, it could be another problem…

    Hey, Mods are fun to do!!! Pick one from this site, or safely invent something yourself. If it works, post it!!!

  92. Micah

    Great information! I have a 30 amp system w/a Coleman rood top a/c that works great except for on very hot an humid days. It keeps kicking the 20 amp. breaker inside. We don’t run the electric water heater b/c of this. Coils and everything are clean. We don’t use a generator and are plugged into 30 amp service. Will the SPP6E help with this? Thanks!

  93. Nick

    Would have saved alot of money viewing this Forum. I bought my first Camper with a 13,500 Dometic installed and it kept tripping the Honda EU3000i Changed to a 12,000 Dometic with the same results, and not worth the added cost.

    So, I traded for a New Camper, New Honda EU2000i, and bought a New Coleman AC Mach1 PS, with a New Supco SPP4E ready to install. But before the Coleman AC goes into the Camper, I have taken the door off, which has a wiring diagram on it. The Coleman Start Cap has two double terminals, the yellow wire leads to the Run Cap which changes to white wire and connects to S on the compresser. The other terminal of the Start Cap has a PTCR plugged on top, with a red wire plugged into that PTCR terminal and leading to the Run Cap, then to R on compresser. It seems like I could just take the PTCR off the stock Start Cap and plug the SPP4E into the two available terminals, adding a boost, to use my EU2000i for easy starts.
    According to Coleman, the Mach1 PS would take approximately 24amps for start up, which was about the same as my bigger EU3000i, that kept tripping by the two Dometic AC, After being charged almost 200 dollars, by a less than honest RV service department, I was told it was too close to max output for the generator, especially if the converter happened to kick on.
    Another question, If the stock Coleman start Cap is 88-108 MFD with 165 VAC and the SPP4E is 88-106uF with 90-130V. Are MFD and uF considered the same, concerning Capacitor Value?
    Also, It seems with the Start Cap and Run Cap strapped together with the Fan Cap?, inside the door next to the Hi Pressure switch and relay. There is limited room to fit in the SPP4E (pretty sure I could do it) But, if I removed the stock Start Cap with attached PTCR there would be plenty of room. Although I would lose the easy plug in terminals for the SPP4E, on the stock Start Cap. At this point, it’s probably best, to remove the PTCR and plug in the SPP4E with the two available terminals, on the stock Start Cap.
    Sure could use some input…THANKS

  94. Nick

    Okay, Guess I’m on my own…took off the PTCR connected the SPP4E to the stock Cap with the two extra terminals (probably there for that reason to piggyback) and yes MFD and uF are the same.
    I hope the electronic version of the PTCR in the Supco SPP4E controls both. Mounted the AC in the camper and will connect wiring, then ceiling assembly by next week. Then will use my Honda EU2000i for running the new AC. Let you all know later. Just in case anyone is interested.
    Truly, Nick 4 now!

  95. Gary

    Hey! I ordered a S6PPE based on what was said in this forum. My A/C is a 15000 BTU unit that I think was made by dometic, but I don’t recall seeing a name anywhere. It was pretty obvious how to hook it up as there was only one giant oval cap in the control box. It had three terminals, one side looked liked it went to the fan (brown wire) and the other went to the comp. (red wire). Hooked the Supco cap up to the red and white wires and my a/c now runs off my kipor 2000 watt gen. Quite amazing, as it would not do this before. Not only does it start the a/c, it does it quite easily. The a/c sounds way better when it starts. Even when plugged into AC shore power it took a second and hummed a bit before it started. Now it really starts well! I’m impressed Thanks! Two thumbs up!

  96. chuck


  97. paul

    I have a 2009 Dometic Duo Therm 13,500 that runs perfectly with my EU3000 running on gasoline even on the hottest days with no modifications. I converted the generator to run on propane (which has a bit less stored energy than gasoline). The generator when burning propane has a smidgen bit of problem starting the a/c but runs great on a hot day once the a/c has started. Here’s the gotcha. When it cools down at night and the compressor is starting and stopping automatically to maintain the temperature inside the RV, the EU3000 handles this just lovely running on gasoline even in economy mode. Running on propane, the EU3000 CANNOT handle the compressor turning on and off at night. It trips the O/L on the generator. Mr. ModmyRV, will this capacitor help my situation?

  98. ModMyRV

    @paul - The boost capacitor might help your situation as it sounds as though your generator surge capacity is down a bit when running on propane. Does the genny struggle at night on shorepower? Is the eco-throttle on or off?

  99. paul

    ModMyRV - Thanks for the response. I think you meant to ask if the Duotherm A/C unit struggles at night on shore power and it does not. I ran it last night on a 20 Amp circuit and it ran perfectly and I know the compressor was going on and off because it was in the low 70’s last night so the A/C unit didn’t need to keep the compressor on all the time. I do keep the econo-throttle on regardless of whether I’m running on Gasoline or propane. I know this saves a lot of fuel because with either fuel source, once the compressor comes on and stays on, the generator runs just above idle. In contrast, if I leave the econo-throttle off, the genny runs full tilt and fuel efficiency goes out the window. With gasoline, there is no problem running on econo-throttle although I’ve thought that I might be hurting the a/c compressior while it tries to start but has to wait the 1-2 seconds for the genny RPM’s to catch up.

  100. Nick

    Actually, I needed to take out the stock Start Cap & thermo-type PTCR, then just simply plug the two wires of the SPP4E, into the Run Cap exactly as the stock Start Cap(removed). Now my EU2000i Honda Gen. does start & run my Mach1 RV AC easily, while on the Economy setting.

    I also called Dometic after viewing their test of the Honda EU2000i, utilizing their Smart Start on the Marine AC-unit. The fact is their Smart Start is only made for Marine AC-units and not for any RV AC-units.
    Thus, I am very thankful for this article by Mod My RV & Supco for their boosters, especially with the Electronic PTCR in the SPP4E, purchased and installed by myself.
    Now a truly happy camper!

  101. Stu

    Replaced the stock Start Cap & thermo-type PTCR with a SPP6 on my 03 Duo Therm 13.5K and didn’t see any difference. When I dial down the thermostat to kick the compressor on from my Y2K gen the gen revs up, AC fan stops running and the AC compressor does not start. Turning the thermostat back up restarts the AC fan. All other breakers are off.

    My AC unit looks just like the one pictured at the top of this page. The original start cap looked the same but the run cap was circular and off white plastic - not silver metal.

    One thing I noticed swapping the start caps was at no time did I get a spark from either of them. Shouldn’t they have had a charge?

  102. Webb White

    A/C on Class c motorhome will not start using generator. It tries but cannot start. Have not tried it on regular 120v house current. Do I need a capacitor? Should I try it using 120 V first.
    Webb White

  103. Webb White

    How do you tell if a 6V RV Battery has a dead cell?

  104. ksmith1123

    I added an SPP6 to the existing 13.5K BTU A/C start capacitor on my ‘09 Arctic Fox 25R TT and now my Honda eu2000i starts and runs it just fine. About 1000 watts and 9 amps average to run it after startup. Had to turn off the econo switch though to get it to kick the compressor over initially but once it started I turned it back on, rpm’ s came back down a little, and all is well. It was 65 degrees at about 800 feet altitude though so not sure how she would do at 90 degrees and 6000 feet.

    Two wires = literally 5 minutes for entire MOD

    As always YMMV…

    EDIT: While in Big Bend National Park at the end of February 2011, we were camped at about 1,800 feet and the outside temp got to 99 degrees! My Yamaha 2400i had a VERY hard time reliably kicking over the compressor each time. We got it going every time but took several tries a couple times. Once running all was good and cool in the TT…

  105. arkybobbie


    I have a 15K penguin Dometic a/c on my motor home. I have blown 4 starting capacitors on the 3 year old unit. I purchased a Supco SPPG6 to install but found out that my current start cap has 3 wires and the Supco has only two. how do i wire the Supco.

  106. Miller88310

    Tried this mod…took me more time to get up the ladder than to install the Capacitor but…my wired in surge protector won’t let the voltage go low enough to start the ac. I’m using a Honda 2000.


    Added the Supco spp6e to my 15k Duo Therm on my 37′ Sandpiper and it kicks off with my Honda 2000i. Had to turn Eco Throttle off but once it kicks on I could turn the Eco Throttle on and the RPM’s came down a little. Absolutely awesome.

  108. mike

    cool! does it matter which wire goes where?

  109. keither

    Hello All!
    Ok so which one do i need. I have read all of this thread and it confuses me more the moretimes i read it LOL! I have a 2010 Jayco BHDS with a coleman 15000btu air conditioner.By the way this site is great! I have been looking for a site like this for a while.

  110. Chuck Beaupre

    I bought both capacitors. I bought a new dometic 13500 a/c and two new Honda 2000i generators with the connector kit for running both. I put the SPP6E in first. Tried one generator and it popped the circuit button on the generator. I hooked the generators together and everything ran fine. I put in the SPP6 and the A/C started. It drug down the generator at startup but then ran great. It really dragged on econo but then ran great. It’s only 80 in the camper and 70 outside at 4400 feet. I’ll carry both generators until I get to higher elevations and hotter days for further testing.

  111. Chuck Beaupre

    As a clarification to my post above, when I switched to the SPP6 and tested the A/C, it was with one generator.

  112. Lyle

    I have a colman scondary ac on the bedroom and here in az its hot, the 88-108 MFD 165 vac start capacitor with the sq thing on top (hard start part)i guessing is out (melted) will one of your hardstart/capacitor products replace mine and if so which one. Thanks

  113. the.lenster

    I have an older Dometic Duo Therm with what appears to be a PTCR and no start capacitor. What would be the proper method to install the Supco SPP6E on this unit? Would I install the SPP6E in place of the PTCR or in parallel with it? I can provide a picture of the unit if necessary.



  114. the.lenster

    Word from Supco is the SPP6E will NOT work on my Dometic Duo Therm. Must be the SPP6 and it wires across the “C” and “Herm” terminals on the Run Capacitor, paralleling the PTCR.

    So, if you decide to do this, contact Supco first and verify which hard start capacitor they recommend for your AC unit. They responded to my query almost immediately and were very informative.

    Good luck!!!

  115. Jojo

    Thanks for solving my problem! I have two Honda2000i gens that kept tripping. I installed the hard start capacator and it worked!!! Before I did this, I realized one battery went dry so the load was already way too much! Just a tad bit of advice from this 50yo gal that’s pretty good at fixing her own suff: make sure everything else is well maintained also! Before I got these generators and decided to start dry camping, I had zero clue about ANY of this. Thanks for the lesson!

  116. Vacman

    My 40′ National with two Duo-therm AC units on the roof recently started kicking one of the 30a breakers on the Generec Generator and occasionally stalling the Gen as well. I was told that it may be the Motor Start/Run Capacitor. My research brought me here to this fabulous ModMyRV site. Wow, great information. One key note was the high Altitude factor. Yep, my problem occurred at 7,000 msl, 98 degree weather! I could run one SC unit, but not both. It sounds like I need to install the Hard Start Supco SPP6 Capacitor, huh? Surely cheap enough to try!

  117. Jim Berry

    If you are adding a hardstart to your RV A/C unit, use the SPP6 [no E]. The SPP6E is not designed for 120VAC applications, The “E” series is also an instant restart unit, this does not allow the generator sufficient time to rampup to full power. The SPP6 has the preferred PTC relay and allows a longer ramp up time. The SPP6 is rated for 120VAC usage.
    Remember for every thousand feet above sea level you generator drops 3% of output. On hotter days the A/C drops in efficiency as well. Check with your A/C manufacturer on the correct generator size for your unit. As far as I know there is not a manufacturer that will reccomend a 2000 watt generator to run a 13,500 BTU A/C unit.
    If you have any questions about the SPP6 or any other Supco part, please contact us at 1-800-333-9125 ext. 261 our Tech Support will be glad to assist you.
    Jim Berry
    Director Product Management
    Sealed Unit Parts Co., Inc.

  118. Scott

    I have a Dometic 13500 BTU unit and the Honda EU2000i. My generator would typically start the A/C unit the first time, but would overload whenever the A/C unit cycled. I got the SPP6E and replaced the existing one. Works like a charm!

  119. gmr3

    I have a Colman model#8333E8564 (AirXcel) Mack 3+ EZ. Want to use 2 Champion 73531i hooked in parallel(rated @ 4000 peek watts/3200 running watts). Changed starter capacitor with a DiversiTech DST-6, still kicks out the overload on generators at start up. Will adding a second capacitor in parallel help or damage the A/C? What is the P.T.C.R. that is attached between the capacitor and compressor?

  120. Kevin Gunning

    It seems that this thread may have incorrect information. I called Supco and they say the “E” will not work well. Most important, the wiring of the SPP6 should be done in Parallel to the RUN cap (Common and HERM) terminals. You don’t need to remove anything.



  121. bobbmp

    Hi I know some asked this, but I didn’t see a response. I have Coleman 13.5 and a Honda EU2000. I bought a SPP8E thinking if a SPP6E is good a SPP8E should be better. Wrong, my A/C compressor won’t start! Any suggestions?

  122. ewarnerusa

    I tried using my Yahama 2400 generator on my new TT with 13,500 Btu A/C and it was able to run it. But I had been warned by the previous owner of the generator that it worked for him, too, when the temps were cool but once it got warm the generator had a really hard time with it. So I figured I would do the hard start capacitor and installed the SPP6E like this mod describes. I didn’t try it out with the generator after the install, but it did kick on using shore power. Then I read these comments carefully about the SPP6 vs SPP6E debate and second guessed my choice. I then emailed Supco directly and the reply was that the SPP6 was the better choice. No E.
    So I decided to order the SPP6. I’ll make someone a deal on a SPP6E that has been used once!

  123. Jim Krause

    Another believer in the spp6e. Before the Coleman 13.5 stalled my Champion 4000.
    After 15 minutes on the TT roof for installation the difference is amazing, barely noticeable when AC starts with Converter/charger running.

  124. Ted Marriner

    Ok, I’ve been searching for the old startup capacitors that used to be sold. I’m trying to help startup a compressor with a Yamaha 3000i generator. In the old days, you could actually purchase a startup capacitor that plugged into the outlet. You then plugged the cord into the capacitor. They no longer sell those. Anyone know if it would be possible to use the A/C startup capacitor or one like it to help startup an air compressor?

  125. sdayman

    I did this one today: SPP6 on a Dometic 13.5k. It has the dual capacitor, so I piggybacked the SPP6 onto the C and HERM terminals. There was just enough room in the capacitor box to wedge in the SPP6 next to the existing capacitor. My Yamaha EF2000iS wasn’t able to start the A/C, even in non-econo mode. Next week when I plug into shore power, I’ll see if/how well the A/C fires up.

    UPDATE: A/C still works normally. I haven’t noticed any difference since the upgrade, though it’s been a while since I ran the A/C to really remember how it used to be. Since the SPP6 is hooked up correctly, I’ll leave it, assuming that it’s beneficial.

  126. CaptainJustice

    SPP6 or SPP6E?

    There is a LOT of discussion about this so I emailed SUPCO. My inquiry was on: Hard start cap for Coleman Mach 15 15000 BTU RV A/C

    And I asked: Which do you recommend for this ac unit? The SPP5 or 6, and what about the “E” class of either? (I asked about the SPP5 because it is rated for 1/3 HP which is what my AC is)

    And the answer was:
    Use the SPP6 [no E]. Also make sure that your generator is rated for 3500 watts or better.

    End of discussion as far as I can see.

  127. 4rjbrooks

    Hello everyone, I’m trying to do this mod, and have purchased the SPP6 (Per Supco) for my ac unit. I have a Coleman Mach (15K btu I think unit). I have climbed up on the roof of my tt several times now, and have taken some pictures of the 3 capacitors that are wired up, as well as the wiring diagram, but I have no idea what to unplug, or how to safely discharge the old capacitors. There is 1 large grey, 1 small grey, and 1 small black. I was told the large Grey is the run capacitor, but was trying to figure out what the others are for, and do I need to remove anything or just add to what is already there. I don’t know how to add pictures to this forum but can email someone if you can help.


  128. HARRY



  129. leftlanetruckin

    I got a Dometic Commercial 13,500BTU rooftop for my big rig.
    I installed a Honda EU3000is on the rig too.
    The ac would run if I started the rooftop unit in ac mode, but would trip the overload on the generator when it cycled.
    Found this thread and started calling around suppliers in my area. I ended up with a SPP7E, as that is all I could get, and need to leave out again today!
    Removed the cover and electrical cover, to find there was NO capacitor in there for the ac! No wonder it bogged the Honda down huh?
    After 5 minutes, it is running like a champ, many thanks!
    Any possible damage to anything by using the SPP7E? The supplier said it was perfectly fine to go bigger, but not fine to go smaller. He also said that the 6E or 7E are the ones rated for the ton size of a 13,500BTU rooftop unit. But if I need to find the 6E, I will do so though.
    Many thanks

  130. Denis

    We sell and install a product here in the northwest on RV A/Cs up to 15000 btu that allows a EU2000i to start and run the unit flawlessly. It is not a capacitor based unit but a SCR based solid state unit that limits the start current to allow the 2000i to pick it up time after time. It is a little more complicated to install but is easier on the compressor and the inverter. There are over 250,000 installed world wide and works well with properly sized solar systems as well as generators. If the SPP6 route doesn’t work out, this is the answer! Contact us at

  131. melvonnar

    Installed the spp6; before I installed the cap the air compresser would studder and sometimes it started and sometimes it didn’t; after I installed the spp6 it starts every time and no studder.

  132. Chris

    Hello, Im getting a yamaha ef2400ishc, so i figured i would install the spp6 since my 3000w kipor had some problems starting my 13.5k ac in eco mode. My zinger is a 2010 with a dometic ac unit. It only has one capacitor, before adding it i amp clamped the hot wire while plugged into my house. It took up to 15amps top start it. With the spp6 piggy backed to the herm and c termanals, the amp draw went up to 23. I still need to get the new generator and try it both ways but shouldnt the amp draw go down with the spp6?
    Thanks, Chris

  133. drz rider

    I am so dissapointed that this mod. didn’t work for me, I’m glad it didn’t take alot of money or time to find out.

  134. Chris

    I have a Carrier Air V. After removing the cover, it seems it has no hard start capacitor. Does anyone know which contacts I connect to spp6 wires to on the run capacitor? From what I’ve read it is H and C. Does that sound right? Thanks

  135. Chris L

    Yes you hook it up to the c and the herm. I dont think it has polarity but i hooked the one with the piggy back connector to the herm. My yami 2400ishc starts mine with or with out, since i saw a higher amp spike with it i removed it for now. Need to figure out if its helping or hindering it!

  136. JoBo1943

    I have a Dometic Brisk Air 7.180 BTU and the SUPCO SPP6E was a total failure.
    Then I looked at the wiring diagram for my unit and it listed a start cap as an option so I dug around and found that Dometic has kits availabale depending on what series of unit you have.

    For modles starting with 41xxx, 457xxx, 459xxx, 57xxx,59xxx 52xxxx, 53xxxx, 54xxxx and 55xxxx the kit is #3310727.007 and there’s one on e-bay for $25.

    If you use the above number for for the model listed below is voids your warranty.

    For modles that start with the number 6 (exampls 620525.331c) the number is 3311883.000

    And for questions call 574-389-3711

    The above is from the “Service Kit Alert” that came with my unit.
    And the value of the cap in my “kit” is the same as the SPP4E Supco unit.
    Why buy something that “might work” if the manufacturer already has one. My Generac iX2000 (2200 surge) now starts my AC mid 90 degree days.


  137. bigocean

    Hello, when adding a Supco SPP6E can I “piggy back” it onto a existing starting capacitor? There are existing terminals on the startup capacitor that I can slide the new wires from the booster capacitor right onto. This article says remove the existing capacitor..but…. Thanks for any help.

  138. Jason B


    Bought the SPP6 through an Amazon affiliate, and they sent me a Supco SPP7S instead. Anyone familiar with these and would this be a viable alternative? I can ship it back for a refund, but wanted to ask the collective prior to going through the hassle.



  139. Jason B

    So, tried the SPP7S. No go. Honda 3k would go into overload each time the A/C kicked in. Pulled ‘er off, and all better. Guess I’m going without, unless I get cheeky and want to try the SPP6 later. Figure I’m at 4400ft and it’s 94 outside, so I should be good.


  140. westxsrt10

    I just decided to try the cap. mod so I bought both types,SPP6E and the SPP6. (13,500btu, Boliy 3600s inverter gen.)
    The SPP6E improved the hard start by about 40%.
    The SPP6 showed no improvement.

  141. ILUVRVing

    Sorry - just tailing / searching the forum(s) - I have a 2006 Cherokee 305B 5er that just started having AC start up issues. After a trip from VA last week that was in the mid to upper 90’s. The AC would run all day, then @ night when it finally reached the stat set temp the AC would shut off, BUT then on start up would blow the 20amp AC breaker. Once back home I tried the AC on my dedicated 30amp circuit and change the 20amp AC breaker in the rig and had the same results. I’m looking to do this mod,(replace~I think) the start up cap to a Supco Mfg. - SPP6 - Hard Start Capacitor, as well as add a fan delay module.

    Another question comes to mind. In my case - IF I’m adding the Hard Start Cap - then is there something in my AC that is going bad (defective) that needs to be replaced (stock cap or something) in addition to adding a Hard Start cap?
    Thanks in advance….

  142. billj0124

    Lots of great info about the Supco SPP6E, but why would Supco’s tech people suggest SPP6 instead of the “E”? I have a (2008)Dometic 15K unit I will inspect this weekend and take a photo of the capacitor in use and post it for review and maybe someone with the same unit can tell which one worked best for them with their Honda 2000i? Talk to you next week…Thx

    I just completed this Mod using the Supco SPP6E and it was very simple! Started my Honda 2000i and my a/c fired right up without any hesitation! I was at 6500′ elevation and very happy that I did not have to buy another generator!!!

  143. evolvingpowercat

    Revised. SUPCO technical support is emphatic that one must NOT remove the existing PTCR and Hard Start Capacitor when adding their hard Start Kit. They confirm their instructions and this how to’s instructions to wire the hard start in parallel across the run capacitor terminals where the existing start capacitor and series PTCR are installed.

  144. nepatoyhauler

    I just completed this mod using a Supco SPP6E because I could not reliably run the Dometic 13,500 btu rooftop air conditioner using my twin Champion 2000 watt inverter generators connected in parallel. Initially the air conditoner would start under generator power but would trip when the compressor cycled. I presume this is because of the increased pressures within the system once the compressor starts. I purchased the SPP6E before I read that the manufacturer recommends the SPP6 when running using a generator but the SPP6E did just fine. This mod really worked for me and the generators have not tripped since completion of this mod. Prior to this mod the inverter generators tripped during the compressor’s first restart during cycling. I also needed an electrical box upgrade to a 6×6x4 to accommodate the larger start capacitor.
    In addition, I highly recommend the twin champion inverter generators connected in parallel. They seem to be a close second to the Honda as far as power but considering they are half the price they take first place for people with my budget. They have performed flawlessly and now they reliably run my rooftop air conditioner following completion of this mod. Yes, I fully recommend this mod for anybody using a small generator.

  145. john

    Just a little confused. I ordered the PTT6E and plan on installing it on my 1997 Dometic Duo Therm 57915.622 air conditioner. Did I order the right one? I am using a honda eu2000i. It would start the air but after 1st use would go into overload and shut genny down.

  146. evolvingpowercat

    I did this mod to a newer 2010 or 2011 manufacturing vintage Dometic 13,500 BTU AC roof top AC unit on my 2011 Heartland Edge M21 RV. Used the SUPCO SPP6E. UPDATE: Jim at SUPCO Technical Support tells me the SPP6E is intended only for 220V compressors, and that the SPP6 is recommended for the 110V RV AC compressor application. So, it is up on the roof one more time to remove the SPP6E.

  147. Chris

    I installed my budies factory start cap and my amperage at start up stayed the same. When i used the the spp6 the amperage went up! So if any one wants to trade my spp6 for a spp6e let me know! Maybe some work with the spp6 and others with the spp6e.

  148. Bowser

    Be very, very careful. I read this description carefully several times, trotted off and bought my SPP6. It came with simple directions Pull out the old one, plug in the new, and away you go.

    Not so easy. The old wires were white and yellow, the new were black, both of them, one with printing on it. I assumed this was the white wire.

    Wired it up, worked fine, no compressor. Switched wires, great sound, no compressor. Have wires coming loose all over the little area, plug them back where they seem to go.

    Now I have an RV with an air conditioner open to the elements, screws all over the place, sheet metal puzzles just waiting for a finger to cut, and a great
    ceiling fan. No compressor, no cool air.

    And I’m not a particular slouch. I built the house I’m sitting in, with my own

    hands, including wiring. Lots of wiring. Build radios as a kid for science projects, and this was before transistors.

    If it sounds too good to be true it is. I would not fall for this one again. I’m not quite sure what to do, probably try to put it back together tomorrow. This mod, in my opinion, is a bust, and that may just reflect the aches and tiredness from having spent 6 hours on someone’s simple mod. And then winding up in much, much worse shape than before.

    As I said, beware. This one is not worth the risk. If in fact it ever did work.

    After three days, getting the schematic from the manufacturer and another half day this thing does, indeed, work and work well. Whereas formerly the Honda EU 2000i would not run the AC in hot weather, today just as a test I started it on the EOC setting, AC on high. Honda started, AC started, on first pull. That is above and beyond the call.

    However, do not try to follow the instructions here or on the little bag it comes in.

  149. Shawn844

    Hello to all, I just did this mod and it worked great. I did change things a little
    Instead of using the supco spp6 or spp6e I used a ICM 860. The ICM 860
    Is good between 1/ 12 to 5 hp and 90 to 380v. I am new to the site and
    Look forward to using more of the mods here on my 99 prowler.
    Thanks , Shawn

  150. Alex McLean

    I fitted the SPP6 about a week ago to my dometic 13500. It was cold and I had to use my wife’s hair dryer to fool the thermostat. My Yamaha 2000ie took the load and the AC ran no bother. I tried it a few times using the econo mode and full load and it started fine. It says in the mod that you will take longer getting on the roof and taking the hood off than doing the mod and thats exacly right. I only had one capacitor fitted (dual) and the SPP6 fits snuggly in with it. I suppose the true test is next summer, but for now I am delighted

  151. Joe O'Bremski

    Not an electrical expert but I do know a little. The ratings on those capacitors is the uF rating (micro farads) not V (volts). The voltage is listed as 300V which means as long as you don’t go OVER 300V it won’t pop. The larger the uF rating the better! In the link below they list the different models:

    SPP5E 1/3 to 2 hp 43uF – 52uF; 330V
    SPP6E 1/2 to 3 hp 88uF – 106uF; 330V
    SPP7E 1 to 4 hp 130uF – 156uF; 330V
    SPP8E 1 to 10 hp 189uF – 227uF; 330V

    i.e. They give a range because it’s not an exact measurement but the uF capacity should be within that range. So from that chart an SPP8E would be about 4 times the capacity of a SPP5E

    Back in my car stereo days we would install 1F or 1.5F (1000000uF to 1500000uF) capacitors in parallel with the amp for those low frequency high loads that would cause your headlights to dim. The cap supplied the extra current to make up for the drop and kept things from going dim as well as keeping the amp at full power. During low loads the cap recharges. It basically acts like a small battery that can discharge much faster then a standard battery can.

  152. mikeintn

    A video showing the install of the SPP6E capacitor. Its not the greatest video but hopefully it will help some.

  153. nepatoyhauler

    Did anybody have clearance issues with the SPP6E capacitor upgrade? The SPP6E was much larger than the factory capacitor and did not fit inside the original housing. This made the job a little bit more challlenging, but not impossible. I removed the original metal enclosure and replaced it with a larger outdoor enclosure from Lowe’s that still fit within the outer housing. I completed the upgrade late last summer and it survived initial tests before cold weather predominated. Still, considering the small price tag and time expenditure, it is a worthwhile upgrade that will enhance comfort during a boondocking experience.

  154. jon van mader

    I just completed installing the SPP6 capacitor in my Duo-Therm 7100 btu rooftop air unit on my camper. Hooked the two wires to “Common” and “Herm”, and now my Honda 2000i gen will cycle the compressor and frig, even in the low-rpm “eco” mode. Without this hard-start capacitor, my little 2000i wound trip its own breaker after one cycle of the roof-air compressor. It took 45 minutes to get the ladder up and remove and reinstall the Duo Therm cover, but only 5 minutes to plug-in the new capacitor. This video was helpful, too.
    Thank You!

  155. spydie

    I called the suppco factory and asked them if I should install the “E” model on my RV A/C (it’s rated 170-250 volt). They said NO… use the SPP6 ONLY. A lot of people are using the E model, but it is no the correct one for 110 volt A/C

  156. nepatoyhauler

    I installed the SPP6E hard start capacitor on my rooftop Dometic Duotherm air conditioner. It was a vast improvement over the factory start capacitor, but still not the correct choice. According to Supco, the recommended hard start capacitor for a small generator should be the SPP6, not the SPP6E. Because of the advanced electronics in the SPP6E, this hard start capacitor is removed from the circuit too quickly, and a small generator, being unable to recover in due time, will trip and go into “overload.” I recently purchased the SPP6 to replace the SPP6E. It may take some time to get “real world results” when comparing the SPP6 to the SPP6E. Hopefully, I can provide a unique perspective having installed both the SPP6 and the SPP6E in the same air conditioning unit for comparison.

  157. Paul H

    I have a Dometic duotherm 13,500 btu A/C unit. My Yamaha ef3000iseb (with boost) running full throttle will start my A/C no matter how hot it is or how long the A/C has been running. My Yamaha will also run my small fridge and lights. What my ef3000iseb will *not* do is start my A/C when the generator is running in “economy mode”. Having the ability to start the A/C when the generator is running in economy mode would save a significant amount of fuel as opposed to running the generator full throttle. Will this mod offer enough “umph” to allow my A/C to start when my yamaha is running in economy mode?

  158. goose8404

    Supco RCO410
    I was told to use the Supco RCO410 but I cannot find any info on installation. Is this able to be used or not? If so how is is hooked up. I have a DuoTherm Brisk Air Dometic 13,500.

  159. mrgehring

    I installed the SUPCO HS6 (SPP6) in my Dometic 13.5 unit, but it seemed to make no difference in my ability to run it with one Yamaha EF2000is generator. Still have to run two to make it work. At least it was an easy mod. Actually, the worst part was trying to get the cover back on to the AC unit, took me about an hour of rolling around trying to squeeze it just right to seat it again. Too bad my wife wouldn’t get on the roof to help me ….

  160. A/C Guy

    Your capacitor may be week due to power spikes, check the capacitance (uf) with your multimeter. In a pinch you can take the capacitor off your microwave and use it wired to the compressor and leave the fan wired to the old one just piggy back commons or run a new common fron the contactor (load side). The rule with capacitors is larger never smaller but not to crazy large.

  161. Tony

    I tried the SPP6E on my Briskair 15,000 but neither my 2K Magnum inverter, 2800 Yamaha generator, nor my 3,500 Honda would start it although the inverter actually tried to start it after the install.

    It did seem to start quicker on my 20A circuit 10ga cord plugged into the house.

    What about an SPP7E or SPP8E? The sticker on the motor said something like 67A start?

  162. Charlie B

    My thanks to the original author for their in depth treatment of the subject. I am on the threshold of performing this mod to my Dometic Penguin unit. I have spoken, in depth to Supco technical support. As nepatoyhauler pointed out, Supco recommends doing this mod using the SPP6 - NOT the SPP6E. In addition, in cases where a start capacitor already exists in the unit, they recommend piggy backing the SPP6 to the existing capacitor, NOT replacing the original capacitor with the SPP6. The reason given is that depending on what is there already, you might actually be putting in a smaller capacitor, which is opposite of what you want to do.

  163. cbvp

    Just did this mod to my Son’s 15,000 btu Dometic AC on his 2006 Cedar Creek.

    Had two 2000 Hondas paralleled running in econo mode. AC kicked in, both gens reeved up for a second then went back to idle.

    Thank you to the OP for this mod


  164. Roboman

    I have a 13,500 BTU Dometic on my trailer that would NOT run with my Smarter Tools (powered by Yamaha from Costco) 2000 Watt peak generator.

    I replaced the stock AC start capacitor the Supco SPP6E hard start capacitor. The AC fired up easily with the my generator after this modification. Picked up the Supco SPP6E off Amazon for $14.99 delivered.

    Greatest mod ever and saved me from having to get another generator too.

  165. nepatoyhauler

    I have utilized two different start capacitors, the Supco SPP6E, which was not reliable because the electronics take it out of the circuit too quickly, therefore tripping my Champion inverter generators. I re-upgraded to the Supco SPP6 and it works flawlessly so far after an hour-long test with my 2,000 watt inverter generators. In addition, the gentleman from Supergen products at telephone# 1-GENERATOR was super helpful and helped me eliminate parasitic loads. Also, for those with an older Champion inverter generator, you can send your control module back to Supergen products, and they will upgrade the software to improve the generator’s power curve, giving it a higher power rating than from the factory.

  166. HammerToe

    Attn: nepatoyhauler Re Your Post of June 26th, 2014 at 12:42 pm:

    I spoke at some length with a rep at Supco 4-5 days ago and in response to my specific question - SPP6 OR SPP6E? - I was told that ‘THE’ one to use was the SPP6 for the reasons you mention. I was also told (again, I asked, should I disable/remove from the circuit the ’stock’ Start Cap or leave it/wire the SPP6 ‘in parallel’, and I was told to LEAVE IT, just ‘add-in’ the SPP6. I also have 2-2KW CPE Inverters and the parallel kit and I’ve also (finally) had pretty good success at (finally, again) being able to ‘drive’ the 13,500 BTU Brisk Air on my 5th. I ‘did’ this mod, but my tests so far have been with (wrongly) the original Start Cap ‘out of the picture’; will have to run some more tests when I get it back in. So far, pretty good success with start and ‘re-start’ on non-eco mode; had gen breakers trip one trying to restart/recycle when the gens in eco mode. Something you said intrigued me - the part about:

    …Also, for those with an ***older*** Champion inverter generator, you can send your control module back to Supergen products, and they will upgrade the software to improve the generator’s power curve, giving it a higher power rating than from the factory…

    ‘How old’ does the gen have to be…? How can one tell (if you know) if one has/has not the ‘better’ ‘power module’???


  167. nepatoyhauler

    Hello HammerToe,
    First, to answer the question about the Champion inverter generators, I believe the models with the silver corner valences are the earlier models, and are rated at 1600 watts continuous and 2000 peak. The models having black corner valences are rated at 1700 watts continuous and 2000 watts peak. When I asked the gentleman at Supergen products, he stated the two models are mechanically identical, simply differing in software, and informed me of the software upgrade which makes the two units identical in regards to output. In addition, another tip he had was to turn the thermostat all the way down. Initially, that seemed counter-intuitive to me, but he said the A/C unit cycles much less frequently when turned all the way down, resulting in fewer opportunities for the generators to trip as the compressor restarts due to the starting watts required. Hope this helps.

  168. Ron

    I have a Coleman 7300 model a/c we started it today and it ran for 30 seconds and now will not restart , when switching on and off I have a clicking noise coming from what looks like 3 side by side relays any ideas of what might be the problem

  169. hawk751

    I have a question on install this on a carrier unit. I installed it but not sure if it is doing any good. Has anyone installed this on a carrier unit?

  170. Mutleyk

    Trying to find out what one I need I have a forest river 2012 sport 260 with a 13500 BTU AC can some one tell me what one I need..

  171. noel

    I have a 1997 Dometic 11000 BTU rv air conditioner . I have an Onan 2.8 kilowatt genset . when I have the generator running and turn the air conditioner on the compressor starts right up . however on the second or third compressor start up the generator will stall . I thought it was the carburetor I put in a brand new carburetor and still have the same problem so it must be the air conditioner unit .
    if I manually control the thermostat and create a five minute delay between compressor start ups the generator will not stall . however, it seems like the compressor will cycle on and off every 2 or 3 minutes and then the generator will stall. I’ve noticed while hooked to shore power at the generator fan blower sometimes will slow down a lot and then speed up for some reason .

    could this be low freon? high head pressure is between cycles ? bad compressor? bad capacitors ?

  172. RoadToad

    @noel… There is a time delay circuit that is supposed to prevent the compressor from attempting to restart until enough time has passed for the head pressure to totally decay.
    Sounds like either the circuit is malfunctioning or the head pressure relief function is flawed. You need to locate a qualified Tech to put gauges and meters on your unit to determine this.
    The time delay is accomplished with a capacitor & inductor circuit.
    Chances are that the capacitor for that is dried out and not forcing enough time to pass. The unit is 17+ years old and atrophying.
    Your Generator set is probably just fine.

  173. Robert Pirie

    I have a jayco 15 ft jay flight swift. My air conditioner is mounted in the wall, will the hard start compositor fit

  174. Moon_man99

    Have a brisk air II. Took cover off and only one capacitor visible. Am I suppose I hook the SPP6 to this or is there another capacitor hidden? The one behind the cover has 3 main terminals with a red whites and brown wires. Will I then just need to mount the extra capacitor somewhere? Thank you

  175. George

    I just did this mod on a Duo-therm circa 1996. What a difference. Not only does the unit run smoother with a softer start, but it is much more quiet than before and my temp is clocking in at 44 degrees (51 before the mod. The parts were less than 30 bucks. I replaced the shroud when I did the mod and it took less than an hour. I also went from 30 /5 mfd to 35/5 mfd on both the run and start caps. Thank You for the great tip.

  176. Cameron

    So, I ordered an SPP6E before reading everything in this thread and hooked it up to the AC and it DID make a big difference. With that being said, the capacitor was so far gone that a 9 volt battery would have made a big difference. So, the debate continues, what is best SPP6E or SPP6? Well, I e-mailed Supco. Below is my e-mail and their response…..As a result, I now have 2 SPP6 units on the way.

    SPP6 VS. SPPG6
    I’m sure you guys get this question quite often as it is a topic of debate over the internet based the different voltage ratings of each; but I figured I would come to the source.
    What product is best suited for my application; the SPP6 or the SPP6E and why?
    I am replacing the starting capacitor in both of my RV roof top Air Condition units. They are both Dometic Duo-Therm units running on 115 volts AC. One is a 15,000btu unit, and the other is a 13,500btu.

    The stock (or at least oem replacement) capacitors are as follows:
    15,000 btu unit – 47-56uF, 250 VAC,
    13,500 btu unit – 43-53uF, 250 VAC,


    We recommend the SPP6 for RV applications, it is a better match for the genset.
    The SPP6E is designed more for a 240V application, and uses a voltage sensing, electronic potential relay. The SPP6 uses a temperature sensing PTC relay.

    Michael Del Mauro
    Technical Support
    Sealed Unit Parts Co., Inc.
    2230 Landmark Place
    Allenwood, NJ 08720
    P: (800)333-9125
    F: (732)223-6979

  177. Robert m taylor

    Have s 2000 model Coleman pop-up w. A Coleman Mach 1. I think AC. Looking to put this in. Thanks

  178. geezer88

    Just did the mod using the recommended parts. My AC is a Carrier 13.5kBTU built in 2001. The Yamaha ef2400is would not start it before, now it does, at least at sea level and 80deg. Next trip to the high desert will be the big test. 8) It is still pretty near the margin, though, because it won’t start the battery charger and the AC at the same time. The charger is a Centurion 20A unit, and I think it must be a switching supply because the surge current is quite high, while running with only a few amps going to the battery, it only pulls 1 amp from the AC supply.

    Many thanks to the folks that posted the hard start mod, and somewhere else the guy that mentioned turning off the charger.


  179. scott summers

    I just bought a brand new trailer with a roof top AC unit (Airxcel) model 48253C969. I’m planning on buying a Yamaha EF2400ISHC gen (20Amp)at full power. I don’t know what the AC unit has for CAPs can you tell me which starting cap I should use?

  180. rstpn

    my 2 roof AC units both turn on fan & compressor i have a diesel onan generator has no problem running both no lag or stalling have 2 50 mp circuit breakers 1 for each unit problem is after 2 minutes they shut off fan & compressor they do not trp the breakers they both will restart after several minutes but cycle off again n again will the SUPCO SPP6E FIX THIS PROBLEM

  181. alligot

    I have a Dometic model 57915, 13,500 So with this mod I can run my AC with a Honda EU2000i?

  182. alligot

    Also which one do I need? Supco SPP6E Or SPP6 ?

  183. stu

    Advice for using a small generator on A/C. We found we could run our 13000 btu A/C on a eu2000i (no hard start cap mod needed) by doing these three things: the obvious - make sure the fridge, water heater, etc are not on. The not so obvious: after the camper sits for a few hours, the lead-acid battery self discharges. Thus if your battery is close to fully charged and healthy, but slightly discharged from simply sitting idle for a day or two, power up your generator and let the campers converter charge the battery for 5 to 10 minutes. The battery charger converter always draws high current until the battery is topped off. The heavy draw from the converter then goes way down and becomes a negligible load on the generator. Trick 2 - if you have a manual ceiling A/C, turn the A/C unit to ‘fan only’ at first and then let the fan run for a minute. Doing this eliminates the A/C fan motor startup current draw, and the grease in the fan bearings warms up slightly, reducing even more current draw. After fan runs for a minute, then quickly turn knob to A/C. If that does not start it, you might try the hard start capacitor. We never needed to install the capacitor. Last, our EU200i always started the A/C every time, by doing the fan on first, when it was not in eco mode.

  184. dlsacco

    I had done the Supco hard start cap, but found it didn’t help as much as I needed. I have since replaced the start cap with a Micro Air soft start unit. WAYYYY better result. It was pricy, but not as much as doing a new generator or generator supporting inverter. There are some youtube videos of a 2000 watt inverter generator starting and running a normal RV AC unit on economy mode. My 2000 watt struggles a bit at my 9000 foot home elevation, but given that derates the genny by 25% not surprised. Going to look for one with a 2000 watt running rating rather than 2000 watt starting rating and should be good to go. Will run the AC when I get down to 5000 ft.

  185. Tim

    I installed the SPP6 on my 2006 Dometic 13.5k btu RV AC. The pics above are identical to my unit. After installing(I put the wire with the extra lug to the HERM or red terminal on the motor run capacitor and the other wire to where the white wire went) the AC did not start well, the fan would run, but the AC would cycle on and off very slowly. I tried 2 brand new SPP6 and both were scary to listen to. I put the old cap back on and it works way better. Any ideas?

  186. Lloyd BC

    I did this mod a while back, on an old Dometic A/C and it worked great. I have since traded up to a newer TT, equipped with an AIRXCEL (Coleman 48000 series 13,500 BTU) A/C. Does anyone have a schematic they could share, to get me pointed in the right direction?

  187. Lloyd BC

    Did some more digging (Google) and found mod info for Carrier, Coleman A/C. So come spring, I will modify my Brother’s and mine.

  188. Lloyd BC

    Well, camping season is here, and I finally did this mod on our 2011 TT.
    We went 6 seasons without ever using our A/C. Last year, in late August, we went camping with my Bro, and tried to start the A/C (Carrier) on his ‘new’ TT with our Yamaha 2400. No Go, so, we tried ours (Coleman). Also No Go!
    So, last week I completed the mod, and now all is well, although the ‘Coleman’ does start quite different to what I was used to with the old ‘Dometic’..

  189. Schluter1966

    I purchased this mod only find out that I already had a hard start capacitor installed. I’m wondering if I installed dual capacitors if it would cause any issues or work better. Crazy i realize but there are enough plugs to connect it.
    Has anyone done this?

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