RV Air Conditioner Hard Start Capacitor

Mod #82: Air Conditioner Hard Start Capacitor

Submitted on: 05/27/09	Category: cooling, featured
Mod Rating: (56 ratings) Loading ...	Viewed: 10131 times
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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:

Supco SPP6E A/C hard start capacitor

Example Dometic Brisk Air wiring diagram

Dometic Brisk Air wiring diagram underneath A/C intake grill

Dometic A/C outside cover - notice all the screws!

Located in the front right of the A/C unit, the utility box contains start and run capacitors

Wiring diagram for A/C compressor motor and blower motor

Close up of capacitors - the shiny one is the motor run capacitor and the black one is the motor starting capacitor

The starting cap is 43-53 uF while the Supco is 88 to 106 uF - theis means more starting power!AC

Typical OEM motor starting capacitor - same as the one shown in the utility box

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!

If 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.

Before 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.

ModMyRV recommends these parts for this mod:
Supco SPP6 Hard Start Assist PTC Capacitor Combination, Voltage (VAC) 90 - 277

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64 Comments For This Mod

Bob Vaughn (May 28th, 2009 at 7:42 am)

I had to have a hard start capacitor installed on my AC at home….
Luke Scholl (June 2nd, 2009 at 8:29 am)

Will a Supco SPP6 work for this application or do you recommend the SPP6E only?
ModMyRV (June 2nd, 2009 at 10:21 am)

@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.
Brad Kahler (June 2nd, 2009 at 3:18 pm)

Where can I purchase the SPP6E capacitor ?
ModMyRV (June 2nd, 2009 at 5:10 pm)

Try here: http://www.patriot-supply.com/products/showitem.cfm/153429
John Weber (June 8th, 2009 at 2:55 am)

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?
ModMyRV (June 8th, 2009 at 6:41 pm)

@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.
John Weber (June 9th, 2009 at 2:54 am)

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?
Steve Carson (June 11th, 2009 at 8:07 am)

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.
ModMyRV (June 12th, 2009 at 7:35 am)

@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:

http://www.patriot-supply.com/products/showitem.cfm/153429

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

http://www.supco.com
ModMyRV (June 12th, 2009 at 7:50 am)

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

http://www.pplmotorhomes.com/parts/rv-power-cords/automatic-transfer-switch.htm

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.
John Weber (June 21st, 2009 at 11:49 am)

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?
plascell (June 21st, 2009 at 4:49 pm)

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.
Bob Pierce (June 23rd, 2009 at 7:18 pm)

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……
Capn_Silver (July 5th, 2009 at 6:30 pm)

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.
Adam-12 (July 6th, 2009 at 1:17 am)

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.
C Collins (July 8th, 2009 at 7:51 am)

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.
ModMyRV (July 8th, 2009 at 8:10 am)

@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.
ModMyRV (July 8th, 2009 at 8:16 am)

@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.
Erwin (July 13th, 2009 at 4:44 pm)

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?
gaweber (July 13th, 2009 at 7:43 pm)

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.
Erwin (July 14th, 2009 at 8:49 am)

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?
gaweber (July 14th, 2009 at 4:20 pm)

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
http://www.supco.com/images/pdfs/E%20Class%20Prod%20Sheet.pdf
Erwin (July 15th, 2009 at 9:13 am)

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
http://www.supco.com/images/pdfs/2009%20HVAC%20Caralog/2009%20Catalog%20for%20Web2.pdf
lavelle pierce (July 16th, 2009 at 8:58 am)

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
73GMCer (July 19th, 2009 at 2:36 pm)

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
73GMCer (July 19th, 2009 at 2:39 pm)

Has anyone successfully used a 2K generator with this mod? A friend wants to know.
wmarsha (July 24th, 2009 at 8:06 am)

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?
Kevin Mcnulty (July 25th, 2009 at 12:20 pm)

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)
Dennis (July 27th, 2009 at 12:10 pm)

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?
ModMyRV (July 27th, 2009 at 12:57 pm)

@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.
TTaddiction (July 28th, 2009 at 8:10 pm)

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.
Dave M (July 30th, 2009 at 4:57 pm)

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?
ModMyRV (July 30th, 2009 at 6:15 pm)

@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.
riverlake (August 3rd, 2009 at 6:35 am)

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!
Dusty (August 3rd, 2009 at 8:16 am)

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.
mlbeep (August 15th, 2009 at 9:12 am)

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…
ModMyRV (August 15th, 2009 at 11:41 am)

@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?
mlbeep (August 15th, 2009 at 2:23 pm)

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!
ModMyRV (August 15th, 2009 at 3:29 pm)

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.
mlbeep (August 17th, 2009 at 9:55 am)

OK, done did it. http://www.modmyrv.com/forums/member-mods/ref-mod-82-air-conditioner-hard-start-capacitor/page-1/post-569
Kevin Mcnulty (August 22nd, 2009 at 9:38 am)

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.
Lloyd Coltman (August 27th, 2009 at 7:57 am)

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
Kevin Mcnulty (August 28th, 2009 at 11:03 pm)

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
Lloyd BC (August 31st, 2009 at 4:48 pm)

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.
EJS4029 (September 9th, 2009 at 9:11 am)

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.

Thanks
Lloyd BC (September 9th, 2009 at 12:54 pm)

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.
jbgreen68 (September 11th, 2009 at 4:22 pm)

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)…
Lloyd BC (September 12th, 2009 at 3:01 pm)

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.
Steve A (September 15th, 2009 at 1:57 pm)

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?
Lloyd BC (September 15th, 2009 at 4:14 pm)

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.
jbgreen68 (September 16th, 2009 at 9:10 am)

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

http://www.supco.com/eclass.htm

Specifications
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.
Steve A (September 17th, 2009 at 8:53 am)

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.
Lloyd BC (September 17th, 2009 at 4:03 pm)

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’.
jbgreen68 (September 26th, 2009 at 4:56 pm)

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:

http://www.modmyrv.com/forums/member-mods/ref-mod-82-air-conditioner-hard-start-capacitor/page-1/post-569

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.
Lloyd BC (September 28th, 2009 at 6:57 pm)

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.
Lloyd BC (October 16th, 2009 at 8:28 pm)

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.
lttlfeller (October 29th, 2009 at 8:42 am)

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!
rrawls (November 3rd, 2009 at 4:35 pm)

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.
chad jones (November 30th, 2009 at 6:36 pm)

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
Barry N. (December 2nd, 2009 at 7:12 am)

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
Barry
jbgreen68 (January 31st, 2010 at 9:34 pm)

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!
EJS4029 (February 1st, 2010 at 12:40 pm)

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.
ModMyRV (February 1st, 2010 at 1:56 pm)

@EJS4029: Maybe this forum thread will help?

http://www.modmyrv.com/forums/member-mods/ref-mod-82-air-conditioner-hard-start-capacitor/page-1/post-569