Mod #100: Honeywell Digital Thermostat

Mod #100: Honeywell Digital Thermostat

Submitted on: 01/03/12

     Category: cooling, heating
Mod Rating: 12345

(103 ratings)

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Mod Description:

This modification was designed and completed by ModMyRV member Lencactustwo. Credit given to Ken Lenger, Alan Paskey and Les Adams for their detailed instructions with their A/C, furnace and digital thermostats. Mine is like all others, slightly different with different wire colors and a Honeywell 5+2 digital. This article carries a copyright. Permission must be obtained from the author before duplication or reposting.

I purchased my unit at the HD for $25 and have seen same at Wally and Lowes for about the same. The switch I found at Radio Shack SPDT (single pole double terminal) but found out I just needed a switch SPST (on /off) for $3.50 as did Les Adams. A little tricky notch in the bottom right corner of the base and back panel to fit. I would do it again but on the left side due to projections on the back of the circuit board.

Mod Difficulty:

My wiring was as follows: yellow wire (always A/C) to Y. White wire to W (for the furnace). Basically all furnace wiring is power wire to white, touch your power wire to the white and presto the furnace starts and cycle thru for about a minute (hint- twist them together to keep you and your loved ones warm while you figure out what else to do) (another hint- twist the yellow and your power wire together to keep you cool headed instead of the furnace).

If you twisted the red wire (typical power) to the yellow or white wire and it did NOT start the A/C or furnace, then try either of them on all other wires until it does. THAT wire is the powered wire and will go on to the R or RC terminal. My case it was the green wire to R/RC with jumper in (u shaped wire between R and RC [furnace and cooling circuits]) Now both A/C and furnace have power when the switch on the bottom is on heat(R/RH) or cooling (RC). Brown wire to G (which runs the A/C fan).

NOW for the tricky part: ALSO put one side of the Radio Shack SPST (on/ off) switch wire into the G terminal and the other to the blue (high fan speed) wire. It works like a tri light bulb 50/100/150 watts, you need 50watt on and 100watt on to get to 150watt, so both wires are powered by the G terminal to get high fan speed, see diagram below that I modified from a Hunter diagram

Don’t worry about the red wire not hooking up, you probably found out it had no power on it, and as the other gentlemen installers noted DO NOT CUT the red wire short as you may need the wire one day for future mods or the buyer of your rig when you sell it down the road may want the old thermostat re-installed.

Remember both the Honeywell and Hunter thermostat instructions were designed for home use not RV use. I have personally installed them in homes and they are exactly as laid out in the instructions: red for power, white for heat, yellow for A/C and green for fan, EASY PEZZY. Us RVers have to follow other instructions!! You know, if they sold one to work in our rigs, it would be 3-4 times the price!

Follow any of the great mods for this UPGRADE to enjoy constant temperatures in your rig so you don’t have to hear “I’m cold…I’m hot”. YES it runs MORE often, but for SHORTER times and more accurately as you can see the digital readout in 1 degree increments, not “kinda between 10 and 20, half way, somewhere, maybe 17 ¼ degrees?” Press either the up/down arrow ONCE to light up the display without disturbing the program and press AGAIN while lit up to change settings for temporary comfort relief (2 hours) or touch RUN to go back to the scheduled settings at any time.

Set up the program in BOTH the heat mode AND cooling mode even if you may not know what you may need exactly, you can always change it. A few degrees different during the night or when you are not in the rig can save you enough to pay for the new thermostat. Save the instruction book for future adjustments. As we are full timers now, I set the weekday program to be the same as the weekend.

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43 Comments For This Mod

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  1. lsgyger

    I did this mod last year after seeing it on a different forum. While placing and connecting the SPST switch is a little tricky, I can’t praise this mod enough! A HUGE upgrade over the stock thermostat! Keeps the temp in the trailer a lot more even, without the highs and lows of the analog thermostat.
    I did keep the stock thermostat in case something would go wrong with the digital.

  2. tkobb421

    Can someone please clarify something for me? The SPST switch is just to set the fan speed (HI/LOW) correct? It would be great if there was a picture of that part of the project.

  3. Portagie68

    Forget the toggle switch. If you got room do the mod the way I did. Add a black rocker switch from NAPA. I put mine in the wall. Used a pop in. Also you have to watch Honeywell. Hunters are better. Honeywell is plus minus 1 usually. Hunters can be set to plus minus 2 which I have been told works better. I got lucky and got a Honeywell with plus minus 2 somehow. Other than that this is a great mod. On the AC you may have to wait 3 minutes before it will go on again.

  4. sdayman

    tkobb421, the analogy of the tri light bulb is excellent. The low wire should always be hooked up. When the fan comes on, it will come on at LOW speed. If you want more speed, the SPST switch adds in the extra juice for HIGH speed.

    To hook up, look at the wiring diagram and the last picture with the little switch sticking out. Mod #37 has better pictures of the switch.

  5. Lencactustwo

    Great idea about installing the switch onto the wall. It would of made this mod easier for me. I gave the moderator the picture of the switch but was not used, The SPST part of the mod is just for the AC fan speed like the one on the OEM tstat and is best described in the graphic picture as I would mount it on the wall next time. Thanks for all the comments on my mod!

  6. Wishbone

    Great mod! I have that exact same Dometic thermostat, and it always seems to be off for too long, and we get cold before it finally turns on.

    What is the model number for that thermostat? There seems to be many similar ones, but I can’t find the exact one in the picture, and none for $25.

  7. Ron

    That SPST on/off switch will work in the on and off positions? What will tell the until to go to high or low ? Is “off” low and “on” high ??

  8. Frank

    I just did this mod today. I used a Honeywell RTH2300B from Home Depot-$25 (I wanted the backlight feature) and a submini SPST 275-0612 switch from Radio Shack-$4.
    I was able to put the switch inside the thermostat as I want to sell the TT in a couple of months so I did not want a hole to fill when I put back the OEM thermostat. I had to cut a notch out of the back plate and inner plate to make room for the switch but it was not hard.

  9. Wishbone

    Just did this mod today.. Used a TH3110D1008. $29 on Amazon. What confused me about this mod is that it only works with the batteries, not with the red power… And the green ground wire goes to the “R” terminal, not the “common”, like it normally would. After I stopped using common sense, and just followed the dang instructions, it worked like a charm!

    I didn’t use the switch.. I just connected the brown and the blue to hard-wire it to high.. I’ll do the rocker switch later if I find this to be annoying.

    One thing to note… The “cool” switch seemed to only work sometimes… It turns out the thermostat has “compressor protection” and times out for 5 minutes if you turn it off and on.. This can be changed or disabled.

  10. Frank

    I’ve read in other forums that if the temp in the trailer is below 32 degrees the Honeywell thermostat cannot “read” it and thus will not work. I do not know if there is also a high temperature threshold as the stored trailer can get above 100 often. I just keep a jumper wire for back up just in case.

  11. taboky

    Have all that have done this mod done it on a Dometic A/C? According to my Coleman manual, and Coleman thermostat, the fan speed wires are energized separately. When I did this mod in my 5th wheel, which ever wire I energized, fan ran at that speed. Just want to be sure.

  12. Frank

    UPDATE to my (FRANK 4/18/2012) post. Last week the outside temp was 104 with high humidity and only dropped to 94 at night. The mod kept the TT at 78F during the day and down to 68 at night (our programmed settings). HOWEVER, the next morning the AC was running but the LCD was blank. I removed the thermostat from the wall assuming the batteries were dead but instead found the inside wet with condensation. I dried it with a hairdryer set on low. I also closed up the 1″ factory thermostat wire hole with duct tape then remounted the thermostat. The problem did not occur the rest of the week so maybe the hole was allowing warm/humid air to enter the cooled thermosat causing condensation and blanking out the LCD.

  13. Scott

    Can the Y2 terminal on the Honeywell 5-2 be used for the blue wire instead of using the SPST switch? in essence the fan speed would automatically change based on need?

  14. Scott

    Update: I performed this mod with the Honeywell 5-2 (6350) and hooked up the high fan wire (blue) to Y2 and it works well. If the temperature variance is greater than 1 degree the high fan kicks in. If you do this, don’t forget to change the system type on the thermo to 1 heat/2 cool.

  15. BrewMeister

    Has anyone tried upgrading to the NEST thermostat?
    Seems like it would be very nice to be able to adjust the thermostat with your smart phone - while out of your coach…

  16. Cho

    Don’t know why you would want to, but;
    if you have an Internet connection into your RV you can use the “Hue” app and any compatible Thermostat to do it.
    BUT; beware that a hack can run your stat up or down and screw you royally.

  17. '04LaredoGirl+4badDogs

    Greetings from 4-snowstorms in eleven-days Boston!
    Bought the thermostat, keep re-reading the posts, still not quite sure what to do; I’ve got red, white, blue, green, grey and yellow wires.
    First question;
    I think I understand that my grey equals everyone else’s brown…am I right?
    Second question:

    I think it goes;
    cap the red
    white to W
    green to Rh/Rc
    yellow to Y
    grey to G

    Third question;
    I don’t understand how I’d add a switch….
    so then I’m down to the blue wire;
    In the interest of not zapping myself stupid, or roasting the coach I’m asking;
    blue goes to G, with the grey wire, correct?

    I’m freezing my buns in beautiful, sunny 38 degree Gloucester, so a definite and timely answer would make my day, but it would make my nights more!

    Thanks for the time and help!

  18. flashdude

    Does anyone know if it is possible to do this mod with an a/c unit that has an electric heat pump for electric heat as well as a propane furnace? My current analog thermostat has a switch to choose between propane heat and electric heat.

  19. Jason

    flashdude - I know your question is from awhile ago… To answer your question, yes! You need to set the thermostat for 2H/1C heat pump. Hook your furnace to W2. If you set it to Emer. Heat, it will run the gas heat only. Otherwise, it will use the heat pump until it can’t keep up, then kick in the furnace and use both to heat the camper…

    I use my Honeywell TH 5000 to control an AC (with heat strip) and a furnace. The heat strip in the AC is ’stage 1′. Furnace is ’stage 2′. Works great!

  20. Jeff

    I installed a Honeywell rth111 tstat using this mod. Now when my furnace comes on to heat, my upper unit fan comes on as well? It’s annoying more than anything. Is there away to remedy the problem?

  21. Teresa

    I just recently bought a used camper from and after a few weeks our thermostat started acting up in our camper. I took it back to the dealership and even though it was a used camper with no warranty they replaced it for me with the model you have showing in this blog. I love it. So easy to use and so easy to set. The thermostat we had before was manual and it was hard to get it set properly. I loved reading your blog and seeing how to do all the things that I want to do to my camper to make it better without breaking the bank. Thank you

  22. RVRob

    I am attempting the mod - bought a Honeywell RTH63500 (5-2 Day). I went to install and I have an orange wire that is going to the HS/HP connector on the Dometic thermostat. The Dometic has Cool/OFF/Furnace/Heat Strip. There is a heat strip installed which we never use. Anyone know what the Orange wire does? The new thermostat has a “conventional” and “heat pump” designations on the wire strip.

  23. RVRob

    Update - I took the best guess and capped off the orange and red. Orange is the for heat strip (found online documents that describe the functionality and wiring) and red (cause the instructions in this mod said to). I can follow simple directions, sometimes. I loaded the batteries and snapped the thermostat onto the base. Nothing smoked and no lights dimmed. Increased the temp and the furnace came on (after reaching temp it turned off). Even tried the fan - switched to ON and the fan in the overhead unit came on - and turned off when I switch back to Auto. I have not tried the Cool - it is only 34 degree here. It is all programmed - we’ll see how the night goes and the 5AM warm-up. Anyone understand how I could connect the orange for the heat strip? Possible?

  24. RVMontana

    Ok we have the analog duo therm wanting to replace it with a honeywell RTH2300B1012A 5-2 day programmable digital thermostat. The issue is th wires. We have pink, red, green, blue, white and yellow. The red is attached to rc, the blue is attached to hc, the green is to g, the white to w, the yellow to y, and pink to rh i believe.

    The honeywell has this wiring config : B, O, G, Y, W, not used, R, Rc.

    How do i connect the wires to the honeywell? We need this ASAP as we are hitting below zero temps and the analog lets the travel trailer get to about 39 before it kicks on when we have it set at 70. no matter what, the thermostat doesnt click until 39 even on 75 so we need to replace asap and our rv repair specialist said its a thermostat issue…

  25. Brutus

    Did you resolve your issues? I have the same Duo Therm and got it all figured out Green wire goes to R/RC, Blue to G, White to W, Yellow to Y, Pink is probably like my orange and others brown probably goes to G for the AC blower. Also when Blue and Pink are both connected to the G the Fan will run on high all the time unless you put a switch on the Blue wire for your AC to run on low otherwise it will run on high always.. Go big or go Home. High speed fan is the only way to fly.. If you decide to do a switch use the snap in rocker switch idea it is much simpler and easy as pie.. It just goes in the line either on or off for high or low. BTW I used the Honeywell RTH221B.. same crap different programming is all.. Mine is working like a champ. OBTW do not use the red wire cap it..or just tuck it in the wall were nothing is touching it. Does nothing..

  26. RVMontanan

    Yes I got this all resolved and i also have it wired, without an additional switch to do both heating and cooling (and i have it wired so we can shut the AC compressor off, but have the fan running, which makes it easier to keep it cool. I ended up using every wire except the one for the low fan.
    my red wire is somehow involved in the ac as it went into RC
    my pink wire is the power for the heater and it went to RH
    my white wire goes to white
    yellow went to yellow
    G went to G
    The remaining wires went to blue.

    While the Honeywell thermostat we put in isn’t exactly like the one above, we an use the ‘heat-off-cool’ switch to switch between heat and cooling (which works here in Montana where we have gone from high 70s in the day to low 40s/upper 30s at night this summer) and when we want to keep the trailer cool without running the compressor (or when the AC compressor freezes up), we can switch it to off and kick on the fan.
    This mod was fairly simple and we had an RV mobile repairman (who by the way encourages people to change the thermostat to give more accurate control over the temp in the trailer.) come out and check the wiring and he ran some tests and said we wired it properly.

  27. newbie

    I have been looking to try and see how in the world this works but I still cant figure it out. from what I can tell all of you have several wires coming from your thermostat. I have 3. Red Black and Orange. I know sounds crazy but that is the truth. any ideas? Red is power. Black is connected to domestic -12v and orange is comms no clue what that means. The rest of the wire bundle is behind the current t-stat but that one just isn’t working. any ideas?

  28. Danno

    I wanted to post about the thermostat I found - It’s a Lux brand, model DMH110 (non-programmable).

    Cool features include a backlight and adjustable “swing” or hysteresis.

    The price online varies wildly, but I found that HomeDepot had it on their website for $18.

    I’m only using it for heat right now (only 2 wires to hook up), but am dreaming of a way to tie in the rooftop briskair unit.


    Completed this MOD last month (10/2014) on my mom’s 2008 35′ Forest River. Recently installed a new wireless T-Stat at home and I just so happened that the original one is the Honeywell FocusPro (# TH6110D1021) pictured in the mod. Install was almost exactly as described. Only difference in wiring was the BROWN wire. Original unit didn’t utilize the brown wire, but instead used the light brown wire (or possibly tan).

    As for the switch, I picked up a 125V, 20 amp rocker switch from Lowes (Gardner Bender 20-Amp Black Single Pole Light Switch). The switch was on installed on the left side of the Honeywell thermostat housing by cutting out enough plastic to slide it in. This required me to fully disassemble the t-stat, slightly bend the rocker switch prongs apart (to ensure no shorts), and then reassemble.

    This MOD works great!! I have pictures for anyone who is interested. Just let me know :-)

  30. Brad

    Thanks to this wiring diagram, I did this mod on a LUX TX500E stat. I didn’t know aboot eliminating the hot wire and using the hot as a ground. That did the trick. I also didn’t know about having to use both fan wires for high fan. I currently only have the high fan hooked up. I tried the AC and the compressor kicked on but no fan. So, I ll have to go back in and connect both the low and high fan wires.

  31. ben31mods

    I like the fan to stay on in the RV. I have found, the temperature throughout the TT stays more even, if I leave the air circulating. I also like to sleep with the fan running to serve as white noise.

    Can I set this to have the fan stay on, even when the furnace is running? If all I hear is the heater coming on and off, I will never get any sleep! Presently, I just use a plug-in electric heater and the fan distributes the heat throughout the TT. If it gets really cold, the electric heater sometimes is on constantly, just to keep up. In those cases, I’d like to add the furnace.

  32. Norman

    Hello All,
    I am a Newbie, am trying to change out my Dometic analog to a digital unit. I currently have a 96 Duo-therm and suburban furnace. any mod help and pics to make both work from same unit would be great. But I am will to use two units as well. I can see the furnace works off 4 wires, but the AC seems to be wired with a ribbon connector. any directions would be great. Thanks Newbie Norm.

  33. Redneckapparelco

    Went to do this mod and we have dometic units but we have a 10 wire ribbon cable going to our thermostats along with the 2furnace wires and 2 power wires any one done one of these before ? Any help would be great

  34. chris

    Tried this to solve ac coming on and off rapidly when set around 85 degrees,but ac didn’t seem to cool as fast(wired it to high setting) and the heat would not work at all….I have a 2006 coachman with a dometic ac system.

  35. Jburbank

    Did this mod but ac turns on when I try to run heat. Believe it is propane only for heat but camper is new to me and still has many mysteries. Air coming out of ac did not feel like it ever warmed up, giving me feeling it was for cooling only

  36. Vic

    I have dometic t-stats that use only 3 wires, red-12v+, green-12v-, brown-comms.
    Any ideas on how I should wire this, have tried several configurations haven’t
    Been able to get it to work.

  37. krbjmpr

    Your Dometic tstat is a single zone, cool/fan or cool/fan/furnace or cool/fan/furnace/heat pump (or strip). It is also a digital data stream. Your control box is controlled by this data stream vs the presence of voltage (or ground).

    The older thermostats, from both Coleman/rvp/airexvel and Dometic, use voltage to turn on relays in a relay / control box located in the ceiling. Since voltages are used, aftermarket residential thermostats are available for use as well.

    You can look around on eBay for used stock, or the rare new old stock, relay box to install into your air conditioner. But you will still face another problem that you only have 3 wires. Make sure its only 3. Pull the tstat off the wall, carefully, and gently pull the 3 wires out of the wall. I wouldn’t be surprised if you saw more wires tied back out of sight.

    For what its worth, 3 wires will turn on air conditioner and fan (1 wire is ground). 4 wires does hi/lo fan plus AC. 5 wires supports previous and furnace OR heat pump. 6 will do the same plus Furnace/HeatPump/Medium Fan, but can only pick 2 of 3. Of course, the sweet spot is to have cat6 network cable, which is 4 pairs/ 8 wires.

    Using a Coleman/RVP control box is very easy, but you will need a Coleman adapter cable from Advent, and furnace control will connect at the thermostat. That might be easier if running wires from furnace to thermostat is possible/easy. Tie in extra set at furnace, and tape off existing in ceiling assembly for future use if needed. I say for future use because sometimes manufacturers will use power from furnace wires to power the thermostat and control box. If you eliminate the ceiling furnace wires, your control box may not work at all in the new configuration.

  38. Jim Veillette

    Thank you for posting pics and this write up. Worked perfectly for me in my 08 Springdale with the Duo-Therm that crapped out and I replaced it with the Honeywell RTH-111.

  39. NaturalStateReb

    Did this mod on a 2009 Keystone Summerland. It has central heat but rooftop air, so doing this mod was very simple–just a couple of wires. The display looks good and it’s far more accurate than the old school thermostat that came stock. Overall, it seems like I’m avoiding the freeze-and-fry tendencies of the old thermostat, which probably means that it’s being more fuel efficient as well. Plus, it’s a bonus to know exactly what the temperature inside the camper is. Great mod.

  40. jim

    Replaced old duotherm with rth111, I tried to do as listed putting the fan and hi fan together but my ac still runs on low speed. Also when running on low after a few minutes the temp reading started going up about a degree every minute or so from what was a temp of 82 when installed to about 94 and i disconnected the new therm and reinstalled the old for now. What did I do with the wiring that could of caused this?

  41. Jason

    I did this mod just recently with great success to my old beauty from 1979 and am happy to say this works great The furnace is a Coleman presidential that is restored and works beautifully with the digital thermostat The old analog type thermostats create a lot of resistance in the furnace circuit which robs power from the blower motor and adds additional strain on the converter but the digital has little to no resistance. Great mod. Thanks

  42. Big Papa James

    2001 Dutchman 31BH Travel Trailer.
    We just replaced the old Duo-Therm thermostat that came stock with the camper with a Honeywell RTH221B 1 Day programmable thermostat. We had the same results that you described and illustrated in this posting. Test the white and yellow wires against the red and nothing… tested against the green and the systems ran. End result, did not use the red wire and do not have a need for a high fan wire (blue). Finished putting everything back together, tested the systems a couple of times and everything is working as it should. Nice to have the turn on before it is freezing cold and shut before it becomes a sauna. Great mod… thank you for posting it.

  43. krbjmpr


    You need to have HiFan connected. I don’t know where you are located, but warmer environments will need the higher air flow.

    Since your tstat doesnt have option to distinguish speeds, you can try what I did. This won’t require any additional parts, just a couple minutes of time.

    Wire FanLo to tstat as normal, and you are correct, you don’t need the red wire (12vdc) for tstat to work as it’s using batteries.

    Put the FanHi wire onto same contact as the Compressor. When compressor kicks on, the fan will change speeds. When compressor turns off, fan changes back to low.

    This way, it’s the best of both worlds. You still have air circulation, and greater cooling capacity.

    If you decide you want low speed only, you can either install a switch, or disconnect wire for FanHi.

    For what it’s worth, the Dometic analog controls were known for 2 things. Failing temperature control at thermostat, and welded relays. For those that have problem with a fan speed, and you have the correct wire, you likely have a welded relay.


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