I need to qualify this first. I have a 22-year-old RV, and there is no fancy climate control involved. It is all simple analog and easy to work with. Newer models with updated climate control may not work with what I am describing. There are also many configurations for how various systems work. That is why Micro Air sells a dozen different thermostats, and you need to buy the right one for your application.
So… Been wanting to do this for some time and finally felt just a little pressure to get it done.
“This” being wire in a WiFi thermostat designed for home use. There are a number of reasons why.
I think we can all agree that the digital thermostats are better at keeping an even temperature than the old bi-metal spring type thermostats.
There are the reasons, but I have to advise that this type of project is not for people who don’t have a pretty good understanding of electrical circuits, how to first figure out what has to happen with the RV systems and then figure out how to marry that to a 24 VAC needed to run a “home” type thermostat.
I have a good understanding of how DC and AC current moves around, and I really enjoy figuring out how to make something work. I have done this with other systems on the Monty and with the 2 Excels I owned previously. The Excels were wired differently than the Montana, but it doesn’t take me too long with a VOM to pin them out and then figure out how to make it work.
In the Excels and up until a day or so ago in the Monty, I used a LUX brand digital (readout), programable thermostat. It was NOT a WiFi thermostat, therefore it had no radio requiring the 24 VAC. It simply used 2 “AA” batteries to run the electronics and the onboard relays, so that was really simple. I had good, even temperatures and programmability, though I never used the latter.
I do not really need a WiFi thermostat in the RV, but I can see times when it could come in handy, say I want to change the temp to cool the rig down when I am an hour away, or simply to monitor what is going on there. If I have WiFi access, it’s all right there.
To make this work, I needed 2 additional parts, aside from the thermostat itself. I needed to source 24 VAC and I needed a relay module that had 24 VAC coils. Amazon to the rescue! I bought a Gaeyaele 4 CH relay module (I actually only needed 3 channels) and I bought a 24 VAC “wall wart” transformer. I would have rather had some kind of low current inverter to go from 12 VDC to 24 VAC but not sure that even exists.
What I am doing with the relay module is using the common and N/O terminals to replicate the OEM RV thermostat switching. Then, I use the 24 VAC signal coming from the Honeywell thermostat to power the relay coils. In thermostat wiring, I need the yellow wire for cooling, white wire for heating, and the green wire for fan. By doing this, the RV wiring is totally isolated from the 24 VAC needed to run the thermostat via the relays.
When the thermostat calls for “cool”, it pulls both the fan relay and the compressor relay simultaneously starting the cooling cycle. When it calls for heat, it only pulls the heat relay, therefore starting the furnace. The furnace FAN takes care of itself, controlled by the furnace, NOT the thermostat. Of note is that the RV appliances (At least this Montana) send 12 VDC to their respective thermostat connections (W,G and Y). The “common” terminal is a ground and by connecting the 12 V to ground it completes the circuit and starts the appliance. I would find it interesting that they didn’t have a 12 V common and send 12 V to the appliance to start it. I think I understand why but that is for another thread sometime.
If I turn the fan from “Auto” to “On”, only the fan relay energizes, not the compressor in the A/C.
One thing I cannot control, at least with the thermostat, is the “High / Low” feature on the fan. I could do this very easily by adding a toggle switch to make or break 1 wire, but anytime I want the fan running, I want it on High. That’s just me. I did have a High / Low switch in one of my Excel’s, but I never used it.
Some of you will figure out how to proceed from here, some will figure what they have is good enough, still others will just buy a Micro Air (or something similar) which is by far the easiest if you want to change. I have about $100 in the project and did it mostly because I could.
This is the original thermostat in my 2024 Montana.
Front and back view of the Lux thermostat I have had in 3 RV's now.
And finally what I just installed, the Honeywell RTH6580WF, a very simple, no frills WiFi thermostat.
I'll post more pics of the install and individual components in the next few days.
So… Been wanting to do this for some time and finally felt just a little pressure to get it done.
“This” being wire in a WiFi thermostat designed for home use. There are a number of reasons why.
- I have 4 Honeywell WiFI thermostats in my home already… What is one more?
- Micro Air, et. al… are very user-friendly but are also expensive.
- Since installing my Victron system, I have power all of the time, even while towing.
I think we can all agree that the digital thermostats are better at keeping an even temperature than the old bi-metal spring type thermostats.
There are the reasons, but I have to advise that this type of project is not for people who don’t have a pretty good understanding of electrical circuits, how to first figure out what has to happen with the RV systems and then figure out how to marry that to a 24 VAC needed to run a “home” type thermostat.
I have a good understanding of how DC and AC current moves around, and I really enjoy figuring out how to make something work. I have done this with other systems on the Monty and with the 2 Excels I owned previously. The Excels were wired differently than the Montana, but it doesn’t take me too long with a VOM to pin them out and then figure out how to make it work.
In the Excels and up until a day or so ago in the Monty, I used a LUX brand digital (readout), programable thermostat. It was NOT a WiFi thermostat, therefore it had no radio requiring the 24 VAC. It simply used 2 “AA” batteries to run the electronics and the onboard relays, so that was really simple. I had good, even temperatures and programmability, though I never used the latter.
I do not really need a WiFi thermostat in the RV, but I can see times when it could come in handy, say I want to change the temp to cool the rig down when I am an hour away, or simply to monitor what is going on there. If I have WiFi access, it’s all right there.
To make this work, I needed 2 additional parts, aside from the thermostat itself. I needed to source 24 VAC and I needed a relay module that had 24 VAC coils. Amazon to the rescue! I bought a Gaeyaele 4 CH relay module (I actually only needed 3 channels) and I bought a 24 VAC “wall wart” transformer. I would have rather had some kind of low current inverter to go from 12 VDC to 24 VAC but not sure that even exists.
What I am doing with the relay module is using the common and N/O terminals to replicate the OEM RV thermostat switching. Then, I use the 24 VAC signal coming from the Honeywell thermostat to power the relay coils. In thermostat wiring, I need the yellow wire for cooling, white wire for heating, and the green wire for fan. By doing this, the RV wiring is totally isolated from the 24 VAC needed to run the thermostat via the relays.
When the thermostat calls for “cool”, it pulls both the fan relay and the compressor relay simultaneously starting the cooling cycle. When it calls for heat, it only pulls the heat relay, therefore starting the furnace. The furnace FAN takes care of itself, controlled by the furnace, NOT the thermostat. Of note is that the RV appliances (At least this Montana) send 12 VDC to their respective thermostat connections (W,G and Y). The “common” terminal is a ground and by connecting the 12 V to ground it completes the circuit and starts the appliance. I would find it interesting that they didn’t have a 12 V common and send 12 V to the appliance to start it. I think I understand why but that is for another thread sometime.
If I turn the fan from “Auto” to “On”, only the fan relay energizes, not the compressor in the A/C.
One thing I cannot control, at least with the thermostat, is the “High / Low” feature on the fan. I could do this very easily by adding a toggle switch to make or break 1 wire, but anytime I want the fan running, I want it on High. That’s just me. I did have a High / Low switch in one of my Excel’s, but I never used it.
Some of you will figure out how to proceed from here, some will figure what they have is good enough, still others will just buy a Micro Air (or something similar) which is by far the easiest if you want to change. I have about $100 in the project and did it mostly because I could.
This is the original thermostat in my 2024 Montana.
Front and back view of the Lux thermostat I have had in 3 RV's now.
And finally what I just installed, the Honeywell RTH6580WF, a very simple, no frills WiFi thermostat.
I'll post more pics of the install and individual components in the next few days.
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