RVP Thermostat Replacement with Digital Honeywell Thermostat

I installed a Honeywell RTHL3550D non programmable digital thermostat in my 5th Wheel Toy-Hauler . I went into the setup menu on the thermostat and turned on multistage cooling fan and connected the high sped fan wire to Y2. If the temp differential is high enough the fan runs in high speed, if the temp differential lowers enough the fan returns to low speed.

In full auto mode, which also needs to be turned on in the setup menu, the thermostat will automatically go from heating mode to cooling mode and vise versa as necessary. In auto a 3 deg separation will be maintained between the heating and cooling set point.

The next time I go to the RV I will get the wire assignments for the Honeywell and the setup menu changes as well and edit this post with the appropriate settings.

This thermostat replaced a duotherm thermostat commonly installed in RV's.


Junior Member
Having a problem converting from analog thermostat to digital thermostat, My rv has 6 wires black,red,orange,blue,yellow& white. My rv has a duo-therm by dometic & I am trying to install a honeywell
Thanks everybody. Been trying for couple days to hookup Honywell thermostat in my rv. Your answers showed me
which wires I had hooked wrong to get hi & low fan.
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
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!
Old one is 12vdc new Honeywell is 24vdc how does it work on 12vdc?