RVP Thermostat Replacement with Digital Honeywell Thermostat

Discussion in 'RV Tips & Tricks' started by Craig Eppley, Apr 5, 2009.

  1. Craig Eppley

    Craig Eppley New Member

    I would just like to share my information on how you can replace your RVP Thermostat with a Digital Thermostat, giving your RV a better temperature control environment.
    I started with going to my local Lowe's Store. I purchased a Honeywell non-programmable digital thermostat Part # RTH5100B. Cost $39.00. I have read other articles using Hunter Thermostats Part # 42995,but I found out they no longer make that model. Then I went to my local Radio Shack store and purchased a DPDT Submini Side Switch, Part # 275-407. There a 2 switches per pack at $3.49. Total cost of $42.49. This is Basically all the major parts you need. By the way if you are wondering why do you need this switch? It will control the High/Low Fan speed for the A/C unit, because the majority of these thermostats on the market are not equipped with the separate switch on the thermostat to control this function.
    Start by removing the old factory Thermostat.
    A. There should be 6 wires attached to the thermostat unit.
    1. Red = 12 VDC + Power
    2. Blue = 12 VDC -
    3. Green = A/C Fan Speed High
    4. Gray = A/C Fan Speed Low
    5. White = Furnace
    6. Yellow = A/C Compressor
    B. Detach these wires from the old thermostat. Remember turn off the Power to the breakers to the A/C unit and the Furnace.
    C Save this Thermostat in your camper incase you have any problems while you are camping,in five mins. you can reinstall the old thermostat to run the furnace and A/C.
    D. Take the Honeywell Thermostat and remove the mounting plate that attached the thermostat to the wall.
    E. Then take the thermostat main unit and take a small straight screw driver and separate the main body of the thermostat. 2 places on the top and 2 on the bottom. Very very easy!
    F. Remove the circuit board from the main body.
    G. Take the back part of the main body, and look at the Lower Left Hand Corner of the Plastic Body. That is where you will install the DPDT Mini Switch to control the fan speed. You will have lots of room.
    H. I took a 5/16 Drill Bit and drilled 2 holes side by side to make room for the switch to slide into each position .Then I took a small pen knife and made the tiny adjustments to clean out the hole where the switch will mount and slide. Once you have finished this part of the installation take the switch and turn it upside down on the outside of the thermostat housing. This will allow you to Drill the 2 holes needed to mount the switch inside the plastic case. You can then drill these 2 holes. Use a 1/16 Drill Bit first! It will fit right through the holes in the switch. Then remove the switch and re drill the holes in the plastic thermostat case with a 5/64 Drill bit. You are ready to install the switch!
    I. You will need to run 3 Wires from the mini switch through the back of the rear housing to the outside rear of the main body once it is put back together again. Look where the 5 metal Prongs of the circuit board go through the rear main body of the thermostat housing. I drilled another 1/4 hole in that area to run the 3 wires through to exit the rear of the housing.
    J. Now for wiring of the switch. I used Red, Green and Gray Wires from the switch to the outside of the housing. This makes it less confusing when you do the final wiring for the thermostat. ALSO DO THE WIRING TO THE SWITCH BEFORE YOU INSTALL THE SWITCH!
    K. The switch will have 6 small and I mean small metal clips standing straight up out of the back of the switch.
    L. Take the RED wire and attach it to the center post of the switch! It doesn't matter which side of the switch just as long as it is the center post. Then Take the Green wire and attached it to one of the post on either side of the switch. And Finally attach the gray wire to the last remaining post. Once these wires are installed on the back of the switch it is ready to be installed into the Thermostat Housing
    M. Install the switch into the housing with 2 of the screws supplied with the switch and run the Red,Green, and Gray wires through the 1/4 hole you drilled in the back of the housing to the outside of the housing.
    N. Install the Circuit Board in the back part of the housing and Install the top part of the housing by snapping it back together! Now you are ready to wire!
    The Honeywell Thermostat wiring block will have the following markings
    1. R/C = Red Cooling.
    2. R/H = Red Hot 12 VDC +
    3. Y = Yellow A/C Compressor
    4. NOT USED
    5. W = White
    6. G = Fan
    O. Take the wiring that you disconnected from the old thermostat and wire as follows:

    1. Red wire from old thermostat to the : R side of the new thermostat
    2. Yellow wire from old thermostat to the : Y side of the new thermostat
    4. White wire from old thermostat to the : W side of the new thermostat
    5. Red wire you installed on the DPDT switch to the : G side of the new thermostat
    6. Connect the Green wire from the old thermostat to the Green wire from the DPDT switch. Connect them together and use a small wire nut.
    7. Connect the Gray from the old thermostat to the Gray wire you installed from the DPDT switch. Connect them together and use a small wire nut.
    8. The Blue wire from the old thermostat should be the only wire you have left over not attached to anything. Tape end of wire up so it does not short out to anything and you are finished. This wire is used for a delay circuit for the A/C compressor,but this delay is built into the new thermostat!
    P. You are Finished! Install the Thermostat housing to the mounting plate and your ready to go! DO NOT FORGET TO TURN THE POWER BACK ON !!!!

    I know this seams like allot of work but from the time I started this Install it only took a Hour and a Half. It is really easy! Now install the 2 "AAA" Batteries in the thermostat and your ready to go. REMEMBER THIS THERMOSTAT WILL NOT FUNCTION OR LET THE A/C OR HEAT OPERATE WITH MISSING OR DEAD BATTERIES!!!!
    Test Run all the furnace and A/C Functions. Remember when you turn the A/C on the Thermostat will have a Delay built in. It doesn't even last 1 min. SO DON'T PANIC!
    Test run the Fan side of the thermostat. Change the Fan selector side of the thermostat from auto to ON. The fan should run then you can change the fan speed using the slide switch you installed.
    I also found out that most RV heating and cooling systems are wired to the thermostat pretty much the same. This is the second one I have done. And the wiring set ups are the same.
    I also found A Temperature difference of + or - 2 Degrees either way. This is a lot better than the old thermostat!
    I hope this information helps someone out there. It is a much more efficient and modern way to make you RV like a Home Away from Home. And If I can do this anyone can do it!
  2. TexasClodhopper

    TexasClodhopper Senior Member

    Re: RVP Thermostat Replacement with Digital Honeywell Thermostat

    Welcome to the forum, Craig!

    Nice job!
  3. twocvsix

    twocvsix New Member

    Re: RVP Thermostat Replacement with Digital Honeywell Thermostat

    Hi Craig. I wonder if you are still there??

    I just purchased a Honeywell RTH 4300B programmable thermostat, and attempted to replace the original Duotherm unit in my Holiday Rambler 5th wheel. Although I have hooked it up exactly as you suggest, including the addition of the slide switch for the two speed fan on the a/c, neither the furnace of the a/c will function.

    Checking the wiring on the Duotherm unit, the first terminal on the left is labeled +7.5, which is more or less what I measure on the wire connected to that terminal. If I understand your instructions, I think you are suggesting that it should be +12 volt. I am measuring 8.25 volts on the second terminal labeled cool, and 13 volts on the next three terminals, labeled Fur, Hi Fan, and Fan. This is with all wires connected to the Duotherm. Your instructions tell me to not connect the Blue wire to the new thermostat. This is the ground wire, or -12volt, as I understand the instruction. Surely, you need this wire to complete the circuit??

    I have the Honeywell all set up, so I don't believe that the problem lies there.

    Any thoughts by yourself, or anyone else that has attempted this conversion would be very gratefully received.

    Cheers, Dave.
  4. twocvsix

    twocvsix New Member

    Re: RVP Thermostat Replacement with Digital Honeywell Thermostat

    Hi All.

    Just a note to say that I have my Honeywell RTH 4300B all working now. I'll list here the connections, as I have them. Starting from the left hand connection on the original Duotherem. The wire that was connected to the "+7.5" connection is no longer used and is now taped up. From the "cool" on the Duotherm to the "Y" on the Honeywell and From the "Fur" to the "W". The wires from the "Hi Fan" and "Fan" go to the outer terminals of Craig's switch, and then the center terminal from the switch, goes to the "G" connection on the Honeywell, (or you can simply connect the wires from "Hi Fan" and "Fan" together and connect them both to the "G" terminal on the Honeywell for single speed fan operation) and finally, from the "Gnd" on the Duotherm to the Jumpered "R' and "RC" on the Honeywell.

    Everything works 100% and I can even use a lower set temperature, because I no longer get the wild temperature swings that I did with the original Duotherm.

    So,,,,,,,,,,,,,,,,, thanks to all that helped with this inexpensive, yet very good conversion.

  5. vanole

    vanole Senior Member

    Re: RVP Thermostat Replacement with Digital Honeywell Thermostat


    Good job on the fix.

    Was your Duotherm thermostat the old 4 button one or the newer 5 button one??

  6. twocvsix

    twocvsix New Member

    Re: RVP Thermostat Replacement with Digital Honeywell Thermostat

    Hi Jeff.

    My old Duotherm thermostat has 3 sliding switches. One labeled "system" with settings cool, off and heat. One labeled "fan" with settings On and auto and one with settings Hi and Lo for the a/c fan. Then there is the slide for the temperature control. So I guess you could say that it has 4 controls.

    I believe the newer ones were actual push buttons with LCD displays, and could control 2 a/c units, as in many of the larger motor homes. My old one has no display and is more or less mechanical.

    Hope this helps.

    Cheers, Dave.
  7. vanole

    vanole Senior Member

    Re: RVP Thermostat Replacement with Digital Honeywell Thermostat

    twocvsix (Dave),

    Thanks for the comeback. Yes the newer ones (thermostats) have LCD displays and can control multiple AC's.

    Once again great job on getting yours to work (read Duotherm work around).

  8. twocvsix

    twocvsix New Member

    Re: RVP Thermostat Replacement with Digital Honeywell Thermostat

    Hi Jeff.

    Where did you find that thread "Duotherm work around" I've looked through this tips and tricks section and can't seem to find it. Any more bits of information that can be found are bound to be helpful.

    Cheers, Dave.
  9. outdoors4ever

    outdoors4ever New Member

    Re: RVP Thermostat Replacement with Digital Honeywell Thermostat

    wow, thats impressive, i would have never thought of that mod!
  10. twocvsix

    twocvsix New Member

    Re: RVP Thermostat Replacement with Digital Honeywell Thermostat

    Nor me, until I found this brilliant forum!! But it works like a charm!
  11. Jocobe

    Jocobe New Member

    Re: RVP Thermostat Replacement with Digital Honeywell Thermostat

    I installed a Honeywell RTH110B without the fan switch and everything works fine, except can't change fan speed. I had both the Hi-Fan and fan wire connected to the G terminal.

    I picked up a SPDT switch from Radio Shack. I hooked it up where the fan wires go to the outer terminals of the switch and the center terminal is connected to the G terminal on the thermostat.

    When I turn on the A/C only one fan speed operates. When I turn on the fan switch, on the thermostat, only one fan speed operates.

    Any idea what's wrong?

  12. twocvsix

    twocvsix New Member

    Re: RVP Thermostat Replacement with Digital Honeywell Thermostat

    Hi John.

    I have to say that When I tested mine, I tried out the heat only, and all was well. You are quite correct. That setup will give you only one A/C fan speed. Here's what you do to get high and low speeds.

    Take the orange wire (or the wire that was going to the "FAN" terminal on the Duotherm) and attach it directly to the G terminal on the Honeywell. You can now discard the extension of that wire that was going to your SPDT switch.

    You should now have two wires connected to the G terminal on the Honeywell. One is the original "Fan" wire, and the other is the wire coming from the centre terminal of the SPDT switch, which, when the switch is in the appropriate position, will connect the "Hi Fan" wire to the G terminal also. By switching the SPDT switch, you will now have 2 speeds on your A/C fan.

    As it turns out, we could have used a much simpler on/off switch to achieve the same result.

    I trust this will help you. If you need any more assistance, please get back to me, here.

    Cheers, Dave.http://www.rvusa.com/forum/mbbs22/images/emoticons/icon_smile.gif
  13. purduepete

    purduepete New Member

    Re: RVP Thermostat Replacement with Digital Honeywell Thermostat

    Thanks for all the coaching on this one. I just finished installing a Hunter model 44550 and it's all working great now! I also upgraded the 12v marine coach battery to two Energizer (Johnson Controls) deep cycle golf carts batteries from Sam's Club.
    Leaving for Las Vegas, NV in the morning via Denver, Arches, Capital Reef, Bryce, Zion and Valley of Fire. Ain't retirement a hoot!

    Pete :)p
  14. twocvsix

    twocvsix New Member

    Re: RVP Thermostat Replacement with Digital Honeywell Thermostat

    Hi Pete.

    Glad it was a help. It's so much better than the old manual one, isn't it.

    Winter seems to have arrived here in BC, even though officially, fall started just the other day. I have to wait until the end of October before I can pull out of here. Heading down to the warmth of Yuma, AZ. for the Winter. Yup!! retirement is pretty good!

  15. ceeyahd1

    ceeyahd1 Junior Member

    I tried the hunter to replace my duotherm and got everything to work except for my furnace, I took it to a garage and they could not get the hunter 42999b to work either, what they found was the thermostat was not sending 12V to furnace and no way this would work. Are there any non programmable thermostats I can use to replace the Duotherm with hi/low fan that would send 12V to the furnace?

    This is what I have:

    Models 39115.601, 39115.602, 39115.616 & 39115.626
    The thermostat is a 12V DC controlled system and is a
    bimetal type. It has three (3) switches on the face of the
    thermostat. On the left side there is a SYSTEM switch and
    on the right side there are two FAN switches. The top switch
    is for HI or LOW FAN and the bottom one is for ON or
    AUTO. This thermostat will operate and air conditioner and furnace.

    Thanks in advance for your help.
  16. H2H1

    H2H1 Senior Member

    Hey Dave thanks for the info, but if you will keep us posted on the cost of gas out that way. I have planned of going the same route, but leaving from Georgis in late May amd going to the Arches, Bryce and Zion NPs. We will be taking in most of the state just sight seeing.
  17. Guest

    Guest Guest

    man hollis ,, i hope if and when u get ur MH to run on a Duotherm thermostat for a furnace ,, u patent it ,, u'll be so damn rich ,, just kidding u ,, i know u prolly posted in the wrong place ,, i have done that many times :mad::concern::distracted::eek:
  18. H2H1

    H2H1 Senior Member

    No ROD I did not posted in the wrong place. I asked Dave to keep me informed about the gas out in the area he is going. That would be the same place as we are planning on going, UTAH, all the NATIONAL PARKS out there. go back and read the post from DAVE.
  19. Guest

    Guest Guest

    ok ,, so now i know ,, but i did not read it all the way ,, i just read about the thermostat ,, sorry
  20. game warden

    game warden Junior Member

    Craig...I have researching this topic all over the internet for quite awhile now and buy far you had the BEST tech advise about doing this mod. I have one question for anyone that could answere this for me. I bought a Honeywell TH5110d1006 (Focus PRO 5000) it is a non programable stat and appears to be just like the one you described in your thread. Hear is my question I have. I own 2012 Keystone Laredo 303tg with a upgraded a/c unit on roof (the std a/c is 13000 btu the upgrade is a 15000 btu) the oem stat is a Coleman Mach and has a red,blue,green,grey,white and yellow total of 6 wires that are hard soldered in to the circut board. I installed the Honeywell as per your instructions to the tee including the dpdt switch,I turned on the heat and it works but i can`t really tell you there is much if any difference in the fan speed......did i do something wrong wiring it ? or does heat only have one speed??I turned the Honeywell to OFF and furnace shut down and then I turned the fan speed on the stat from auto to on and the roof vents started to blow and just for kicks i flipped the switch on the lower left back and forth and it makes a difference in fan speed for sure
    My question is this now since I got this all out ...is this correct opperation????my old coleman stat left me change the fan speed for the A/C and I am not sure about the heat setting if it has a low and high setting..can you tell me f heat is supposed to have a high and low speed also ? or is it just a/c that you have that ability?

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