Mod #37: Digital Thermostat

Mod #37: Digital Thermostat

Submitted on: 07/14/08

     Category: cooling, heating
Mod Rating: 12345

(217 ratings)

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Mod Description:

The standard analog thermostat found in most RVs doesn’t control the A/C and furnace with much accuracy. The “set” temperature is not always the temperature the thermostat cycles, which results in as much as a +/- 5°F temperature change before the A/C or furnace cycles on or off. This is known as the hysteresis of the thermostat. For example, if you have the furnace set at 72°F, this could mean the temperature would fall to 67°F before cycling on and rise to 77°F before cycling off! These temperature swings aren’t very comfortable so what to do? The digital thermostat mod of course.

Mod Difficulty:

Analog thermostats have what’s called a mechanical heat anticipator, which essentially tells the thermostat when to cycle. Some anticipators are more accurate than others but for the most part are not very good at controlling temperatures accurately. The digital thermostat is much better at temperature control since it controls its hysteresis using electronics to within +/- 1°F degree of accuracy.

This mod is commonly performed using the Hunter brand residential thermostat. It’s cheap and very straightforward to install. Other residential thermostats can be used but this one seems to be the most popular. Just be sure the thermostat you select is battery powered. Some residential thermostats use 24 VAC to power them. But if they have the battery backup feature, they can be used for RV 12-volt systems.

The wiring diagram above assumes you have a Dometic A/C unit and an Atwood furnace. Other combinations such as a Coleman Mach A/C unit and a Suburban furnace are very similar so be sure to consult your A/C and furnace manuals to ensure correct wiring. See the resources below for some really nice write-ups by fellow RVers who have performed installations with various A/C-furnace combinations.

ModMyRV recommends these parts for this mod:

General Reference
Hunter Digital Thermostat Installation
Coleman Mach to Hunter Digital Thermostat Instructions

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124 Comments For This Mod

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  1. cccale

    This is a great mod! i only did one thing differently. i spent a couple bucks more and got a programmable thermostat. i have it programmed to turn on the heater in the early morning so we can wake up to a toasty coach!

  2. ModMyRV

    Yeah, the programmable t-stats that manage both heating and cooling timing are pretty nice, but a little expensive. The one in this mod is about $25 but having the automation is cool (or hot?). :)

  3. cccale

    they’re not too bad. Lowes has one for $29

    The one i bought was $40. I spent the extra $10 because it had a slightly larger display.

  4. Bob Vaughn

    I am so happy with the control I now have of my temps… mechanical thermostat was awful In order to get the heat to come on I had to slide the leaver to over 90 then play with it to get it to where we wanted it….in the AC mode I had to take it down to 50 to get it to come on and then play with it..The swing was about 10 degrees……so out with the old and in with the new….as my ac has a high and low fan switch I had to rewire a toggle switch into the bottom of the unit….the instructions on how to do this was on one of the rv forums…..

  5. Bob Vaughn

    From what I learned doing this mod I was able to figure out what was wrong with the thermostat in my daughters house….So now I will be doing a mod at her house…

  6. Bob Vaughn

    Here is my Hunter Thermostat along side my outside/inside thermometer

  7. tvman44

    One of the best mods I have done, sure beats that cheap analog stat by keeping the temp constant. Very easy mod.

  8. Kurt

    My thermostat had two stage cooling. So I hooked up the high fan wire to the second stage cooling contact. The A/C now runs on low, but if the temperature difference is two great it then switches automatically to high fan. You can only one the fan on low setting thought if your running fan only.

  9. ModMyRV

    @Kurt: Hey that’s an idea I haven’t heard of before. Good call. I may have to try that. What brand and model of t-stat are you using?

  10. rvoutreach

    Great mod. Completed mine today and it was very easy to do. I was even able to use the existing mounting holes of the OEM thermostat.

  11. JayAre62

    Easy to do upgrade. I used the Hunter 42999 and added a SPST mini slide switch for Hi/Lo fan speed control. I kind of rushed thru my initial troubleshooting so… after I got the thermostat installed, I discovered my Hi speed relay was also faulty and I ended up replacing the PC Board/Junction Box (as an entire assembly) in my ceiling plenum. The end result is fully functional a/c.

  12. Jason

    I performed this MOD - great AC improvement. I used the Hunter t-stat in the article. I wired up the ground connection and incorporated a small 3.3V voltage regulator to eliminate the need for AA batteries.

  13. Lloyd BC

    I have an old Duo-therm 58915 (wall mount thermostat only), that I’m trying to get operational for a friend. Our problem is that his trailer was never wired for wall mount. Do you think this mod will work if we mount the thermostat on the ceiling next to the return air grill, and use it to control the air only (not heating)?

  14. Portagie68


    What Model T-Stat did you use. I have the same type of system and need to change my T-Stat

  15. ModMyRV

    @Portagie68: Here is a link to a 2-stage thermostat that may help you with you mod. It is similar to the one that @Kurt is referring to:

  16. ModMyRV

    @Lloyd BC: Well, it would work but would be controlling the temperature based on the air temperature near the ceiling. If the ceiling gets hot (from the sun beating down on the roof), the A/C would run longer thinking it needs to cool more. You would have to compensate for that when setting your on/off temperature.

    Is it possible for you to mount the t-stat on the wall near the ceiling? That would help with false temperature readings…

  17. Lloyd BC

    We could possibly wall mount it, but it would probably be on an outside wall, with about the same insulation value as the ceiling, so I don’t see what difference there would be in sensing. Most non-ducted units sense in the return plenum, and they have little or nothing in the way of insulation there. Consider the ‘Sunchaser’ I’m using, no insulation of any sort on the plenum (I think maybe I’ll buy a closed-cell (ensolite) sleeping pad and cut and glue it to the ouside of the plenum when I’m up there doing the start capacitor mod). This is just another way they went Cheap-O on this unit (Single control, single speed, no start capacitor).

  18. stewartfan

    I Like this but I have 120 volts AC at my yellow wire at the unit mounted thermostat.
    Can a thermostat like above handle and switch 120 volts AC?

    Reading some more, I see that this is a “replacement” for a wall mounted thermostat.
    I do not have a wall mounted thermostat to control my AC unit, the controls are mounted directly on the unit.

    I think I will take this Idea and switch a 12 volt relay and wire the the normally open contacts to the existing thermostat wires.

    Do the older thermostats switch 120 volts?

  19. Lloyd BC

    I think what you’re dealing with is a typical non-ducted, integral control A/C, like my old ‘SunChaser’, with the sensing unit (thermostat) mounted in the return plenum. Yes, they do switch 120V. They’re basically just an automatic, temperature controlled, on-off switch for the compressor. I think you will find that these digital units will not handle much more than 24V, if even that. So, if your unit works as is, I would leave it alone.
    Like Mike says, sensing at the ceiling isn’t too accurate, especially if there’s no insulation on the plenum. But it’s better than no cooling at all, in 100+f temps.

  20. Portagie68

    ModMyRv. Making procress on my conversation using the 2 stage T-Sat you suggested. One part I am having a small problem with is the relay that He used to control the high/low fan speed. Have you got any suggestions?

  21. routemaster

    I have no field wires in my Everest bedroom were we had a Coleman Mach instaled.Bought the hunter stat dont know how to wire it into the AC,Do you use spade conectors.Any pics of how you do this in the AC,what guage wire do toy use, please.

  22. Portagie68

    Got the relay numbers from Kurt. He used 5Z486 and purchased it at Grainger. Grainge also says the relay 1EHE3 maybe a good sub.

  23. Portagie68

    My bag. The relay number is for the Hi/Lo Ac fan only.

  24. mickdund

    I have the same set-up in my forest river wildcat,dometic therm.I replaced it with a Hunter model # 44110 works great.I used the same wiring diagram printed from #37 mod.I found a good deal on a Honeywell RTH 7500 therm,it has the automatic heat to cool change over which I think would work great during the fall during temp changes.I tried installing it with same wiring diagram from dometic to hunter,everything works great on it except for the a/c and the heat come on at the same time,any suggestion on what could be the problem.

  25. Terry Kennedy

    I am looking for a 12 volt digital readout thermostat to control my 12 volt refridgeration aboard my boat.

    Any ideas, and prices would be great… Terry Kennedy

  26. wowlites

    Wow…awesome mod. I used a basic Honeywell digital. Easy to install and works like a charm. No more wild temperature swings in our 5ver.

  27. mrseas

    I think this is a great mod! I have a question concerning doing this mod on a Coleman brand A/C heat pump any ideas on how to wire the T/stat?


  28. Dave Border

    Could you just hook up the high speed AC wire on the fan terminal, and have high speed only?

  29. ModMyRV

    Sure can and that’s how I did mine in a previous TT. Worked just fine.

  30. DaveB

    Thanks, I’ll switch the wires today and make sure high speed fan comes on.

  31. original

    Have you seen the Ecobee Internet Enabled programmable thermostat?

    If you haven’t it’s here:

    It’s $469.00 though. I know, I know…excessive.

    But cool!!! (or hot?) >haha<@ModMyRV February 24th, 2009 at 9:35 am

  32. DaveB

    Fan did not come on either way. Did more looking on the web, found another fellow hooked fan and high speed wires to terminal G. Fan now works in high speed mode only, no need for the SPST switch.Fan only switch on thermostat also works correctly now.

  33. jgmccoy

    I have a 2009 jayco pop-up. would this mod work for me? I Do have roof top ac but I control it with the knobs. how ever its my heat I would like to operate with this digital thermostat. what do you think?

  34. ModMyRV

    It should. Since your pop-up is new, it should have the “standard” thermostat most newer units come with. What brand is it? Have you removed it and looked at the wiring?

  35. fireman_tom

    I just did this mod on 2009 keystone Cougar, works great.
    Vary easy to do to.

  36. davidp

    how would you install the digital thermostat if you have two airs and two thermostats?

  37. RoadToad

    One tstat per unit. Like it is now.

  38. RoadToad

    OR, if both stats are mounted at the same location next to each other; then, both Yel on Yel terminal; both Wh on Wh terminal; etc etc. The tstat is nothing but a switch that makes closures to close a connection or open a connection. The “digital” aspect determines “when” to do so. If you wish to route two sets of wires through one stat, you can; so long as the A/C units are electrically the same. (i.e. both switch the “hot” side of the circuit or both switch the “low” side of the circuit). If the A/Cs are the same Model they definitley qualify.

  39. Rolling Condo

    One of the best things you can do to improve the heating in your RV. No more wide swings in the heat cycle.

  40. davidp

    Did the mod with the hunter therm.easy to install by the instructions on mod #37…..Thanks modmyrv….now going to get one for the back air…

  41. gafftaper

    My TT’s thermostat just has two wires, they are not labled but are colored Red and White. I’m looking at buying the Honeywell RTH221B1000, a basic programmable with an on/off switch, for only $24 on Amazon. However I’m not sure how to match up the wires. The manual says it is fine for two wire operation but doesn’t say which two wires to use. Ideas?

  42. RoadToad

    Go here for the manual:

    It looks like your stats wires are for heat only.
    Para; 2.3 shows the White to “W” and the Red to “Rc/Rh”
    Hope this helps.

  43. gafftaper

    Finished the mod tonight took less than 10 minutes and a screw driver. As noted above got a $24 thermostat on Amazon. VERY easy mod and it works great. I look forward to more efficient heating.

  44. amsoiltek

    I did this mod on Sat. while camping this Easter weekend I used the programmable version.

  45. Bob

    I am trying to contact some body from your company. I have a Coleman -Mach thermostat in my RV. It has fallen apart and I need a replacement ( upgrade or what ever) The numbers on the rear side are as follows AG78390-0026, 6535-335. The skew number is F72871012300. If there is some one who can help me out I most certainly appreciate it. Either another web site or address would help . Another thermastate or upgrade , even where ever it Takes .


  46. RoadToad

    Just replace the ’stat as outlined in this (above) “mod” article.
    Read the comments and pick a replacement to your liking; buy it; install it. Almost any thermostat can be used. Follow the “install” instructions. Basically, label the existing wires with the terminal ID letter they are currently on (G, W, etc)and put them on the same terminal of the new ’stat. It’s really not difficult.

  47. zealander

    I replaced the Dometic analog unit in my trailer with a NOMA digital nonprogrammable unit from Canadian Tire. It was about 30 bucks. Simple install and it really works well! I didn’t hook up the high speed wire on the A/C fan yet. I’ll put that on my “get to it later” list!


  48. Michigan

    I currenly have a Duo Therm Analog Thermostat (3107612.008). It is a 6 wire with the Ground wire being Green. I want to replace it with a Digitial programable Thermostat. I am looking for information on the correct unit to buy. Thank you for such a great source of information. I would appreciate it if you could send a response to my email.

    Thank you.

  49. jfdrewett

    I have a Coleman Mach 15kbtu. Used the Honeywell t-stat workes great.


  50. BradWalls

    This is a simple mod that just makes sense……

  51. Jason Lutes

    I love this idea to stop huge temperature swings. I do have a question … While heating for example will this mod make heater fan come on and off every couple minutes? or would you recommend leaving fan on whole time and would this mod allow that?

  52. brad

    I did this mod on our new travel trailer , and it works perfectly, i spent a little more and bought a honeywell programmable auto cool auto heat and it maintained the temperatures right on the dot.i could not have been happier…

  53. Pierreexplorer


    Where did you guys get the wires from the a/c unit? Mine is 120v ceiling mounted with no wall thermostat

  54. dtb72

    It took more time to get the thermostat out of the package than it did to install it and it works great

  55. RE_Todd

    Did the mod this weekend, Easy and quick, took longer for me to clean up my soldering skilss than to do the mod.

  56. BR

    Easy mod and works great. I only have a surburban furnace with roof-mount AC being separate and for this, it’s just a two wire hookup. I used a Hunter 42995 ($20 at Wallmart.) Just follow the wiring in the instructions for a two wire heating system.

  57. Alan Gibbons

    I have a Dometic Duo-Therm A/C and an Atwood 2 Stage Hydro-Flame furnace on a Glendale Titanium Fifth Wheel. The unit came with an Atwood Hydro-Flame Model 2H2C Digital thermostat.
    The hysterisis is plus / minus 4 degrees F., so when set to 75 degrees F. the A/C doesn’t come on until it hits 79 and goes off when it hits 71 degrees F.
    I would like to use the Hunter digital thermostat approach, using a Lux TX1500E (recommended by Lux for the RV) but am confused about the wiring.
    The Atwood thermostat has the following terminals as shown in the manual:

    #1 12VDC Ground
    #2 Not used
    #3 12VDC Positive
    #4 Relay Com (* it says to move jumper to positions 3 & 4 for RVP Unit, and discard for Dometic)
    #5 A/C Compressor
    #6 A/C High Fan
    #7 A/C Low Fan
    #8 Furnace

    I connected the Lux as follows:
    A/C compressor connected to “Y”.
    A/C High Fan connected to “G”.
    Furnace connected to “W”
    I wasn‘t sure what wire from the Atwood unit should be connected to “RC” and “RH”.
    I didn’t know what to do with the “Relay Com” wire, if anything.

    Can anyone help?

  58. original

    Replaced the Coleman Mach with a Honeywell Digital non-programmable RTH111. Just put electrical tape over the blue wire (formerly used for power on the coleman), and also on the gray wire (used for low speed fan), and put nothing on the O/B slot. The rest of the wires were easy.
    Yellow (cooling)/
    Green(High Speed Fan)/

    If I get around to getting a switch, I’ll add the low speed fan back into the mix, but for now it’s all working great, and I’m impressed with how well this keeps the temp at +/- 1 degree F.

  59. Karen

    Hi I was wondering if anyone could help me out? I need to know how to turn off the hunter 4299B thermostat. Please let me know if anyone knows. Thank you.


  60. morrisy18

    Just did this mod while camping over Memorial Day weekend. I used the Hunter Just Right thermostat since only my heater is connected to a thermostat. It was a piece of cake connected two wires and the heater kicked on right away. What a difference as far as temp accuracy. My only complaint is that since this is so much more accurate I noticed my heater kicking on & off a lot more. Is this going to drain my batteries faster?


  61. Larry

    I did this mod with a Lux tx500 model and it worked great. I had planned to incorporate the hi-low switch but after running the the coleman thermostat in high and low I noticed no difference in speed or output. It was the same for the heater and the AC. I finally dicided to put only on fan speed witch made the conversion very quick and easy. The truth is…after thinking about it, we never changed the speed of the fan, it was always on high anyway.
    By the way, the Lux thermostat has nine adjustable setting for sensitivity. I set it at level 4 and this gave me a one degree on either side of the set point.
    Great mod, many thanks

  62. Wolfwalker

    Well, have bought all the stuff and done the work and just need to mount and wire the unit….had a few projects to do before I got to this one; install 2 100lb propane bottles with new supply hoses-done install new limit switch on water heater and element-done except the element as I can’t get the old one out. repair one water line and then it started going below 0 degrees. hit -30 last night and doing everything to conserve propane….hoping to finish the stat today!!! Easy mod so far..great idea. Bought mine at walmart just the basic 19.99 one.

  63. whammon

    Just joined up…this mod is something I have wanted to do since 2005. Trying to locate the Hunter 42996 (mod shown above) with remote but it seems to be discontinued. Does anyone know where I can locate one, or know of another digital thermostat with remote I can use? My trailer thermostat is analog and not real dependable. Need the remote option too. Please help if you can…

  64. Mike Bucalo

    Does anyone have a wireing diagram for a Dometic Penguin heat pump?#651515 I found one at a garage sale(brand new) at a great price. The lady didn’t know anything about it. I just want to see if it runs, before I invest any more money in a ceilling control supply & return panel.Thanks.

  65. Bill Gross

    Would this mod work with dual A/C units? The thermostat I have right now allows me to set the temperature separately in the main living space and bedroom of my 5th wheel.

    Anybody done that?

    Also one with a battery backup (just to retain the settings) for when the rig is at the storage lot.


  66. Wolfwalker

    I finally did this mod!!! Very simple and straight forward instructions. I couldn’t find the remote one and didn’t really NEED it and bought my unit at Wal-Mart for 19.99. Works great.

  67. matt

    Hi there, this seems like a great but i’m wondering if anyone has ever done this for a simple heat only unit. Currently I have an Atwood 38453 tstat. I haven’t taken it off the wall yet, but i’m wondering if this will work for what I have. Can anyone help?

  68. ksmith1123

    So I did this mod about 6 months ago and I just changed back to the old thermostat. Everything worked just fine but the heater kept cycling on and off all the time because of the sensitivity of the new thermostat. Our TT is well insulated but it didn’t take long on a cold night for the temp to drop one degree and kick the furnace back on. Often if would come back on before the old cycle was done.
    Afraid I was going to drain the batteries too fast and then be a in for a really cold night after that…

  69. rt700

    I did this mod yesterday in about a half hour. I used the Hunter 44110 because it was programable. I used a micro mini switch because it hid within the unit better. My wiring colors were a little different, but if you take note when taking out your old unit, they should be well marked and you can figure it out pretty easily. I tested it out and it worked perfectly. Setting the program was a piece of cake and we are really looking forward to using it on our trip next weekend.

    This weekend I’m putting in the Xantrex Freedom SW 3000… now that will not be a 30 minute job!

  70. Larry Walker

    Hello camping freinds
    I’m new to the forum and have already found the mods to be very helpful, like the screen door plexi glass mod.
    I’m wanting to do the thermostat mod but not sure if i can.
    I have the Dometic remote control and this thing is off by about7 to 8 degree.
    Has anyone did this mod with the remote controled unit.
    Thanks for any info Larry

  71. slb714

    I hooked up my hunter and when I put it on cool and put it in Auto the compressor kicks on and stays on all the time regardless of temp. then the fan starts when its gets to the set temp.??? please help im confused

    Duo-Therm stat — Hunter stat
    +7.5 (red) — not used
    Cool (yellow) — Y/O
    FUR (white) — W/B
    Hi Fan (blue) — G
    Fan (brown) — G
    GND (green) — RC & RH(jumper)
    is this right??

  72. gordon gary

    What about a carrier a/c unit and standard 2 wire heater that the heater red/white wires are run to the a/c unit board and both are controlled by a remote t-stat. Would like to add digital t-stat. Thanks.

  73. kerry

    We are replacing our colman thermostat with a basic non progrmable honeywell…our compressor is not kicking on……we know which wire is the compressor….orange….and we know the compressor works….we can figure out what we are doing wrong any suggestions

  74. LRH

    I have a Duo Therm A/C unit, a Suburban furnance, and a Duo Therm stat. Can I replace the stat with the Hunter 42995? Has anyone done this mod with this combination of components.

  75. Murphy

    How do you deal with a/conditioning+furnace+heat strips? This is a 3 way duotherm system.

  76. Kris Lanning

    I have wanted to do this mod forever but my system sounds more complicated than most. I have heating in 4 zones from a hydronic unit and there are 4 roof A/C’s with heat pumps incorporated. These are all controlled by one thermostat that controls each of the 4 zones. There are temperature sensors in each of the zones. The thermostat is digital, but I don’t have programabilty and making a mad dash to turn up the heat on a cold morning is never pleasant.

    Any help would be apreciated.

  77. leslyons

    I carefully read all the info from the various posts on installing a digital thermostat, and then checked out the various thermostats. Long story short - here’s the most updated info and what I installed. The Hunter thermostat which many have installed (Model 42996) is supposedly no longer available. Besides, I wanted to REALLY upgrade and put in a fully programmable model which would: 1) be designed to run off batteries if no power is present; 2) fully programmable for workdays and weekends; 3) automatically switch from A/C to Heat when needed for those Spring/Fall days where it is cold in the morning and hot during the day.

    I researched both Honeywell and Hunter, and talked to tech support at both companies. Although I liked the features, installation instructions and tech support better at Honeywell, I was not convinced their models would work in an RV installation. In fact, the Honeywell tech support assured me they would not!

    So I reluctantly went with Hunter. Researched all the models online, and then went shopping online and at Lowes. Believe it or not, Lowes had the best prices (even better than Amazon), and I bought the Hunter Model 44860 for $59, less my 10% military discount (Good job Lowes!). My research shows this model actually states that it is designed to run on batteries if a power source is not available (i.e. 24v). If you read about this model, you’ll quickly discover that the owner’s manual and installation SUCKS. In spite of that, it’s a great thermostat!

    Don’t even TRY to buy a small SPST switch and drill a hole in the cover and install it as indicated elsewhere. There is NO room! And I melted the small switch with my soldering pencil (I’m all thumbs when it comes to soldering). So I went shopping at Radio Shack and found a GREAT solution for the high-speed / low-speed fan switch for my DuoTherm setup. You can buy a SPST Rocker Switch, #275-0693 for $3.19. It is brown and has nice big spade terminals. Then buy a package of Insulated, Crimp-on, Quick Disconnects (female spade connectors), #6403049 for $2.19. Easy as pie! Just get about 18″ of small gauge wire (9″ for each lead), use two of the small female crimp-on 1/4″ disconnects (22-16 gauge), cut your 18″ wire in half, crimp a disconnect onto the end of each of the two wires, and plug both wires into the spade terminals on the back of the switch. Then use a small plastic wire nut and connect one of the two wires (doesn’t matter which) to the blue (high-speed fan) wire. Connect the other wire to the terminal on the thermostat that has the low-speed fan wire attached to that same terminal.

    This switch is nice, since most RVs have the rocker switches. I wanted to be sure that when the rocker is flipped up it is on (like the other switches in my trailer) so I hooked an ohm meter up and when the side of the rocker with the little white dot is pushed in, the switch is “on.” So you can mount it in your wall right below your new thermostat so when you “push the dot” it is in the up position, and it is partially hidden and meets the “WAF” requirements. (Wife Acceptance Factor!)

    Just wire the thermostat like the rest of the posts here tell you. No sweat! The biggest challenge is to get the little rocker switch mounted in the trailer wall by spinning on the screw-on nut on the inside of the wall! I was able to stick my fingers into the thermostat wire hole and using two fingers, carefully screw it on while holding the front of the switch with my other hand. I’m warning you - it takes a LITTLE patience!

    Everything worked great! Search online for others who have been frustrated with programming this little jewel and you will find posts about how to do it. I’m still learning.

    I hope this helps, and anyone wanting to put in a fully programmable thermostat can use this info and not spend hours researching like I did! Plus, if something goes wrong and it doesn’t work, just take it back to Lowes for a refund! If this thermostat didn’t work, or for those of you who want a programmable thermostat for less money, go to Lowes and buy the Hunter 44110. I’m doing this from memory, but I think it’s around $20!

    UPDATE: It’s now 24 hours later, and I think I’m going to “downgrade” to the Hunter 44110. This automatic changeover from heat to cool, although good in theory, is difficult to implement in actuality. For example, on a early cold morning you may want the internal temperature to be 72 degrees when you get up, but then in the afternoon, when it’s hot, you may want the internal temperature to be 71 degrees to be nice and cool in your RV. I may be a dummy, but I don’t think you can do that, since there needs to be a “span” between heating and cooling. There’s no way (to the best of my knowledge) to “tell” the smart thermostat that it’s too hot and you want to cool it down to 71 degrees, and at the same time in the morning tell it that it’s too cold, and you want to heat it up to 72 degrees. Maybe the 44860 is a lot smarter than me. The 44110 has a manual switch to change from heat to cool, which makes it easy. I’d love to hear from anyone who has solved this dilemma!!!

  78. Curtiss

    I have a 24ft. Sunnybrook 5thWheel and my thermostat is connected to the AC unit via what looks like an RJ11 (4-connector) wire/cable. As my thermo just gave out I’m needing to replace the Hunter 44110 is a VERY affordable alternative to the $280 Duo-Ther upgrade kit. Can anyone give me some advice on how to hookup the Hunter via the RJ11 plug? Thanks!

  79. George

    The Hunter thermostat as a timer for my LP water heater. I was unable to find an inexpensive DC timer so I used the Hunter.
    Now we stop cooking water at 11:00 pm and it allows the heater to start run only between 7:00 AM and 11:00 PM. After all it is just programable timer with a set of dry contacts and a temperature sensor. I will be putting a timer on the AC electric heater soon.
    Hope this helps
    Any other ideas for timer use.

  80. Jan

    Auto change over thermostats have a 3 degree differential between heating and cooling unless user progams it higher. Can’t be programmed lower than the 3 degrees.

  81. Tom Goodrich

    Upon surfing the Dometic website this morning, I see Dometic now offers a Single Zone LCD Thermostat that replaces their less accurate analog Thermostat. I just ordered one for my RV through Camping World at $104.40. With tax and shipping, the cost was: $111.55. They offer 3 models and the one I ordered was: 3313189.023. That part number is for a white thermostat that controls the furnace, air conditioner, and heat pump. They also offer 3 models in black.

  82. Steve

    GReat website for RV DIY, really. I took on the Hunter Digital Thermostat swap when my Duotherm went out and changed both the box and compressor head unit. Great info. Feels like home and can program….. park for the week and by friday its ready for the family. But to the point have you any suggestions for a Duotherm HeatPump and maybe with the heat strip for emergency heat and to take the quick chill out. I am readig the service literature and comparing the to the available tstats. Any advice. to use the oEm tstat would be easy but I want to make my rv mine. Know it like my home. I’m rampling sorry. Idk to make it call for heat at the furnace easy, at the heat strip IDK with the heatpump maybe too muck to take on. I am in a temperate climate in Texas that on occacation in late Feb and MArch it dips but that it the rest is warmer. I would like to not use as much propane and not the space oil radiators.

  83. mongrell

    ok, I’m looking for a simple and inexpensive programmable stat to control and Espar diesel furnace in a boat. Not any different from the RV world. replacing a 2 wire mechanical stat that is just an on off switch for a 12 volt dc circuit. The brain box on the furnace does the rest. I have spent hours on the phon ewith both hunter and honeywell tech support folks, who have minimal english language skills. All of them eventually claim nothing digital is compatible with my DC system.

    My reasoning is that anything with a couple AA batteries would work for this. Is there some mystery to this i can’t grasp???

    The only reference I see in the couple years of this thread is a hunter 4999, but it is non programmable. The next person said they paid a bit more for a programmable stat, but didn’t mention the model number.

    It’s always more fun to buy toys that work on the first go around!


  84. jrtcampers

    Thanks for this mod! We just did it and it’s working beautifully!

  85. infinitezest

    I have a Duo-Therm anolog thermostat with the following wire diagram as described in the manual:

    +7.5v (Red)————– +7.5
    Compressor (Yellow)—— Cool
    A/C Fan Low (orange)—– Fan
    A/C Fan High (Blue)—— Hi Fan
    Furnace (White)———- Fur
    Ground (Black)————Gnd

    I want to update to a Honeywell Pro4000 TH4110D1007 that I have.
    The following is the Terminal Designations for the Pro4000.

    C - 24Vac common. For 2-transformer systems, use common wire from cooling transformer.
    B - Changeover valve energized in heating
    R - 24 Vac power from heating transformer
    Rc - 24 Vac power from cooling transformer
    O - Changeover valve energized in cooling
    G - Fan Relay
    Y - Compressor contractor
    W - Heat Relay.

    There is a factory installed jumper between R and Rc. I have a Suburban gas furnace and a Dometic A/C. I understand I can have a low and high speed fan with an additional switch. I don’t think I need it as the fan stays on high.

    I would appreciate any advice on how this should be wired. I have contacted Honeywell and they wouldn’t help at all.



  86. 2003wrangler

    I used a Honeywell TH 221 and the micromini switch from Radio shack. Wired it today and was pleased that everything worked as planned. I drilled 1/4 inch hole in side of base plate and mounted the switch. had to mod the inside of thermostat to accomadate the switch. The wiring diagram was very helpful, at first couldn’t figure out the use of the green wire to the RC terminal.

  87. Kevin

    Just performed this mod on our Bullet 188 EXP TT. This TT’s original thermostat only controlled the Atwood Furnace, so the wiring was very simple. I went to our local Menards and found a close-out Noma programmable digital thermostat for only $13. It was big enough to cover the old thermostat’s location, but not too big to look gaudy on the wall.

    Since I only had two wires coming to the old thermostat, it was pretty straight forward to connect them to the R and W terminals on the new thermostat. It shouldn’t make any difference which one is attached to which terminal since you’re just splitting the power, basically.

    The only stumbling block I ran into was that the batteries provided with this close-out unit had expired and were dead. I thought I had wired something wrong when things didn’t work. After checking everything out, I tried new batteries and everything started working.

    Thanks again for this wonderful web site. I’ve done two of these mods now (37/100 and 95)and have been very happy with the results. My next mod is to figure out replacement LED lighting for our more primitive camping trips…


  88. burdicda

    I looked everywhere for clarification on this mod
    All the tips have RW + RC jumpered with a “BLACK OR GREEN” wire ground going to them….that didn’t make any sense electronically to me so I put together a schematic diagram and just installed the mod last night…it works perfectly in cool, heat, fan speeds, everything.

    RC and RW are unjumpered in mine since each could theoretically have a different power source, otherwise you could be working on one alone and the darn thing energize on you from the other units power source.

  89. Pat

    Is there any way that this mod can be adapted to control a old style roof a/c that is not controled by a wall thermostat? Thought I saw details on one of the RV forums somewhere.

  90. Matt

    Completed this mod tonight with a LUX Smart Temp TX500E from True Value. Followed the wiring diagram in the pictures, but connected both the fan (orange) and hi-fan (blue) to the G terminal instead of the extra switch. AC fan runs on hi in fan on mode and Auto cool mode. Everything works perfectly. Easy mod!

  91. Alex

    I have an older 1990 Carriage 40ft 5th wheel. I am looking to do this mod, however currently my AC and Heater each have their own thermostat unit. AC is a Duo-Therm control, Heat is just a basic spring based (guessing 2 wire, have not pulled it off the wall yet) thermostat. Could I wire these both into one? They are only a couple inches apart on the wall. I was looking to use the Hunter 44110 so it can be programmed.

  92. Steve

    I just upgraded my old analog Coleman Mach thermostat (which at times had apparently just given up trying to measure temperature altogether) with the Hunter 44155c Programmable thermostat ($24.99 and stocked in store at WalMart). This model also has the “Indiglo” lit lcd background which I REALLY like.

    No problems installing at all, and all functions work. I wired as for a single high speed fan only, as that is all I ever used anyway. I just need to program it now so that when I wake up to jump in the shower before work it will be nice and warm already!

  93. A Clark

    For those who dry camp, digital thermostates,if powered by the RVs 12v system, may not function when the batteries are even slightly discharged. I solved the problem by keeping my mechanical thermostat as a furnance back up, so the RV would not get too cold if the batteries are low, but still able to run the furnance RV

  94. Steve255

    I have a Single Zone LCD Thermostat by Dometic #3313195.000. Does this thermostat have the same +- 5 degrees issue as the analog thermostats that everyone here is replacing? I have a 2011 Eclipse Attitude and am wondering if the newer thermostats have the same issues??? Any info would be great…..

  95. taboky

    Steve255, probably don’t have the temp swing with the digital thermostat. Reason I replaced my digital was to have the programmable feature. Nice waking up warm in early spring/late fall.

  96. tim

    Hi, I have a 1995 dou-therm 3105356.004 thermostat with 4 wires and ribbon for connections. I want to upgrade to a thermostat that will allow me to set the heat temperature around 40f the current one only goes to about 60-55f. Do you know of any solutions for this?


  97. fredm51

    I did this convertion this weekend and it was really easy. The problem is that it never said exactly what is happening with the thermostat. The thermostat connects the +12v thru a relay to the furnace lead or the AC and also to the fan switch be the furnace or the AC. The switch connects the 12v to the high or low fan speed. It does not need 12v or 24v because the 2 batteries supply power to the relays, this is why you do not use the -12v lead on the thermostat. Using this you can figure any digital thermostat that uses battery backup.

  98. homeroller

    I have a 2012 Puma 253 FBS 5th wheel.
    The installed thermostat is a Dometic single zone LCD model 3313192.
    Nowhere I can find in the set up and owners manual,if there is provision for hysterisis adjustment.
    It is installed in the hallway between the rear dining/living area and the front bedroom and I am having stop and start temperature differences of +4 deg. high and -5 deg. low.that makes for very unconfortable tempereture swing.
    Anybody has had similar experiences with this rather expensive thermostat.
    This is actually the exact reason why I am going trough these posting,because I maybe doing something incorrectly and/or I should envision doing this mod to gain accuracy and practicality at a lesser price.
    Comments will be very appreciated

  99. Phil

    I did this conversion and the only issue I have is the fan speed switch. In the wiring diagram it looks like one side, low speed, or wire to the fan is always energised and you are switching an aditional signal on and off to the high speed side, is this correct. Right now I only have one speed.

  100. Albert

    Jason: you had mentioned that you have done this upgrade and used a 3.3 voltage regulator. My question is how did you hook up the regulator? I am considering this mod and I am really interested now that I dont have to worry about the batteries. Please explain how you did it …Thanks

  101. arntzj

    Albert, I used a LE33 regulator with tantalum capacitors on the input and output. Since the Rh and Rc pins are tied together for a coleman RV setup, I re-purposed the Rc pin to connect to trailer ground (normally not connected for battery thermostats).

    So here is my setup:
    Remove the circuit board from the housing to gain access to the back side. I didn’t show the capacitors in the pic below, but one should be put across the input of LE33 and one the output of LE33.

    GND -> Rc pin—x x————| Cut next to the pin, then short the trace to Rh (right next to it)
    +12V -> Rh pin——————|
    |—Vin on LE33
    Vout on LE33 —BAT+
    GND on LE33 —BAT-

    Comp (Y) -> Y pin
    Heat (W) -> W pin
    Fan (G) -> G pin

    If this doesn’t help, I can take a picture, let me know.


  102. albert myers

    Jason, I somewhat get what you are saing but, if you had a pic or diagram that would be great.. Thanks

  103. Jason

    I’ll put something (diagram or pics) together tonight. Have you bought your t-stat yet? Which one did you decide to go with?


  104. albertmyers

    yes,I have bought the t-stat. I got the Hunter #42999 just like the one at the top of page. That would be great if you could get pics/diagram together. You can e-mail me @ . thanks for your help.

  105. Jim

    Is there any replacement for the 3 wire heat/cool Dometic t-stat in my ‘12 Cougar 327?

  106. David Howell

    I am in the PTAC business. PTAC is Package Terminal Air Conditioner. These are the small heat/air units typically found in hotel rooms. A much simpler solution for upgrading your RV thermostat is to install a PTAC digital thermostat. Why go with a PTAC thermostat? Because they have a low and high fan speed selector already built in! The best choice for this application is Friedrich thermostat #RT5 or #RT6. These are battery powered digital thermostats with low and high fan speeds already built in. They are available from any HVAC supply house for about $40. Details regarding this thermostat are available on Friedrich web site

  107. chiefbj

    couldn’t find the 42999 thermostat so I used a 42997 and so far it works as advertised…. thanks

  108. Mitchell

    Was going to replace Dometic analog tstat with Dometic digital for $110. After seeing this post, opted for the Hunter solution. Found it on clearance at Lowes for $14.99. Since we don’t ever use low fan, jumpered hi and low fan wires to G terminal. Installed and works great!

  109. Gary

    I just did this mod. Works GREAT. Furnace and a/c don’t kick on and off anywhere near as much as they did with the old analog t-stat. But I’m worried about the batteries going dead, and would like to install the relay mentioned here. Is this a 12v to 3.3v relay? And could someone give me the “for dummies” version of wiring it in?

    Do I need to solder the output wires to the battery terminals? And exactly which wires (red & green?) go to the relay input?

    If I don’t wire in the relay, how long can I expect batteries to last if I live in my RV year round?

    Thanks, Gary

  110. Old Timer

    This is a great suggestion for camper improvement. You can use any battery-operated thermostat that requires batteries in order to operate and NOT ONLY to retain memory. Be sure to consult with the makers of your particular thermostat so that they can advise you on the best way possible to wire your existing 2 or 3 wiring set-up (there’s a specific way to do it in either case). If it’s a reputable company, they will advise you correctly and honestly that their battery operated thermostat will work, but a good and honest tech. will walk you through the correct steps for your particular application, so be sure to press for answers.

    Here’s a warning example why you would need to consult with the thermostat’s manufacturer first:

    “The only “SAFE” option is to use the “E” terminal for heating activation and the EMER switch position.

    This is a HEAT PUMP thermostat, and is expecting a compressor / condensing unit to be the primary heating and cooling source, connected to the “Y” terminal. Physically you could use the “Y” terminal in HEAT mode (instead of the “E” in EMER mode), however this would produce a safety hazard. REASON = If someone were to inadvertently switch the thermostat into the COOL switch position, this would produce what we would call a “runaway heat lock-on” condition. The thermostat would be calling for the “Y” terminal expecting the ambient air to get cooler, and would keep the “Y” terminal energized permanently (with the heat running non-stop) as the ambient temperature would get hotter and hotter, until the operating output of the heater were reached (i.e. well over 125F degrees).”

  111. Frank D

    Here is a pdf file I created using a LUX DMH110a non-programable digital thermostat for my Heartland North Trail travel trailer. Some info is trailer specific, but all info is usable no matter what type of RV you install this thermostat into. This product has Lux Thermostat company support where hunter doesn’t.

  112. Dennis G

    Will this work (or is it worth it) if my A/C unit is operated by separate controls? My roof mounted A/C controls are mounted on the unit face so the existing t-stat has nothing to do with the A/C.

  113. Carla

    I am trying to replace a Duo-therm by Dometic with a LuxDMH110b. I have no paperwork with the TT so having a hard time figuring out the wiring. We have a 2002 Forrest River 26 ft Sierra. Any help or ideas would be greatly appreciated


  114. klenger

    I found this forum while checking hits to my website, This looks like a very nice place with lots of useful information supporting one of my significant passions. I have recently moved my website from a conventional web hosting site to a WordPress hosted site, and in the process, needed to rewrite all of my pages. An unfortunate side-effect of this is that all of the links to my previous web pages no longer work. Most all of the information is still there, just in different places.

    There is a link on this page to a page on my website regarding digital thermostat installations. If the admin can correct that link, it should be helpful to everyone trying to see the page.

    The correct link to that page is now:

  115. tprothma

    I used the Hunter basic blah, blah model. My wiring was totally different and
    Wire Purpose, Desc, Designator
    +12v (Red), Rh————– +7.5
    Compressor (Yellow)—— Cool
    A/C Fan Low (orange)—– Fan
    A/C Fan High (Blue)—— Hi Fan
    Furnace (White)———- Fur
    Ground (Black)————Gnd

  116. tprothma

    I used the Hunter basic blah, blah model 42995B under $20 from Walmart. My wiring was totally different. On my AC/Furnace grounding Rh and Rc would render the system useless.

    I was replacing a Duo Therm thermostat with Dometic AC and Atwood furnace.

    The furnace wants 12V switched to the time delay relay to turn on the motor. The 12V comes in to the thermostat as Rh. The AC wants another voltage switched to the compressor and low/high fan relays. This comes in as Rc from the AC control box. The T-stat merely switches Rh (12V) to the furnace wire (white 12g wire) to heat. The AC wires are 18g bundle of 4 wires (red, blue, green, white). To run the fan the T-stat switches Rc to fan relay wire (Green for low). To run the fan high, you have to connect the green wire to the high fan relay wire (blue). To run the AC, the T-stat switches Rc to the compressor wire to energize the compressor relay.

    Wire Purpose, Duo Therm Analog, Hunter Digital
    +12v (12g Red), Rh, Rh
    Furnace (12g White), W W
    From AC (18g red), Rc Rc
    Compressor (18g Yellow), Y, Y
    A/C Fan Low (18g Green), G , G
    A/C Fan High (18g Blue), H, manual switch to G

    To adjust the amount the T-stat cycles on/off you can set the span from default of +/-1 degree to +/-2 degrees.


  117. cj

    For those of us with ceiling mount AC units with fans than run continuously. No need to reinvent the whee.

    Coleman (Rv Products - division of Airxcel, Inc.) sells a control system with thermostat. They are around $60.00 and available from Amazon to PPL. Rather than try to pull wires, just run them across the ceiling and wall using some attractive cable/wire covers that are a available in a multitude of sizes and styles at home and electronic stores.
    Coleman Cool-Only Control Package (with thermostat) - #8330-752

    Dometic is, as usual, more complicated and expensive. They do have relay kits and thermostats. If I’m reading correctly, they use ribbon wiring so you can’t substitute an inexpensive Honeywell thermostat. Kit is around $120.
    Dometic Single Zone LCD Thermostat and Control Kit - 3313189.000
    I may have that part number wrong, but it’s a place to start.

  118. Redneckapparelco

    Dometic duo therm 7 wire ribbon cable
    So i purchased the dometic upgrade for digital thermostats after getting them I called them and then they tell me they will not work have to buy new units. I have looked through this many times and would like to make sure that this mod will work for our units. Can anyone help us please ?

  119. C.J. Smith

    I have a 1998 Fleetwood Southwind, with two ACs and two furnaces.
    The thermostat is Intellitec, with a control box I guess in each AC unit and temp sensors in living area plus bedroom area.
    Can this system be used with newer digital thermostat(s), or a single thermostat?
    Thanks…and if not, boy am I jealous of people who can change their thermostats.

  120. dkwagon702

    I have installed a wifi capable 24v tstat in both my 98 Salem and 07 four winds t24. It’s a complicated system but I guess here it seems to be a unheard of mod. If your HVAC unit operates on 120v you can install any type of t-stat currently on the market. Including the nest. The knowledge of relay,transformer use is a must but you can do it!

  121. Jared

    I couldn’t find the hunter any more but I did make a thermostat from The Home Depot work you can checkit out here.

  122. montgomeryAL

    I did this MOD last month in our 2014 Prime Time Avenger 27RLS. It was easy and We are very happy with the results. Since we never used the low seed on our fan I didn’t bother with the added switch. I do think that with the thermostat being 6 inches from the side of the television we are going to be getting a false reading no matter what we have, I’m not sure how wise it is to place the thermostat in the TV cabinet.

  123. Travis

    Thank you for this. I spent a while in a 90 degree 5th wheel trying to figure out the wiring. This was the only one that matched my setup.

    I did not install the switch yet for the fans because I don’t want a toggle. I’d like to use a micro slider instead and label it. For the time being I put the blue into the “G” slot to run it on high at all times.

  124. Jason

    SO, if it is 78 degrees in your RV, and the thermostat is set for 78 degrees, should the unit be ON or OFF? Let’s discover why it is impossible to make it be exactly 78 degrees everywhere in your rv at the same time and on command.

    What you have missed firstly is that there is actually no way to keep the temperature exactly at one setting. The thermostat would never know if it were right or wrong. Instantaneous measurement doesn’t indicate trending. In other industries, it’s called hysteresis. In this case, we need it to happen. In a controlled fashion.

    The unit has to cycle through heating to a few degrees above the set temp, then cool just below that target temp a few degrees… the old stats had mercury or a spring which had to be either ON or OFF. AT temperature… which was it? what’s next… ON or OFF? You can’t tell.

    whether it’s digital or analog, that swing of a few degrees high to a few degrees cool is all you are trying to narrow. what is important is that it is always changing… up or down.

    And also important, where have you placed the measuring device? Are you going for an average 78F across the vehicle… or do you need every square inch of every surface inside your ride to be *exactly* 78F…? You didn’t discuss that either. But your article leads people to think that it would be *eactly* some temperature.

    If you place the stat too high, or too low… it will effect that. So you need several monitoring points, if you’re working on an average. Otherwise, you need a way to measure the temp at every point in the rig (or container) to try to determine the trending (up or down?) to decide if the 78 you see at one point is right or wrong… whether the unit should still be OFF or not… to keep up with the heat load and be *exactly* 78…

    It’s not magic, it’s not snake oil, one stat isn’t any better than another in this respect because it’s all RELATIVE. All you are changing is the amount of variance from the target temp… and even the cheapest stats used to afford a way to do that. Now, 3 to 5 degree swing is std. Even if it’s a hunter, a dometic, a coleman, an atwood, a nest… etc.

    Between 76 and 80 is what you’ll get for a setting of 78.

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