Upgrade RV Thermostat to Nest

We have a relatively modern RV, from 2021, and yet it still came with an archaic analog Coleman-Mach thermostat. It turns out, upgrading an RV thermostat to something halfway modern isn’t trivial as it runs on 12V DC, along with most everything else in the travel trailer.

Thankfully, I found this video on YouTube from Rick James Bish, that walked me through adding some relays and a 24VAC adapter so I could repurpose an unused Nest thermostat in the camper! (Our camper has solar panels and a 120v inverter, so we are able to drive the 24VAC adapter pretty much any time we would want heat or air conditioning in the camper.)

In my case, I just needed to buy the 24VAC adapter, some thermostat wire, and the recommended 4-relay board to make everything work. Since the relay board came with a DIN rail attachment, I actually ended up buying a 6" DIN rail to securely fasten the board behind an access panel. I thought this was a cleaner solution than just dropping it behind the wall and potentially having to fish it out in the future.

Overall, it took about an hour and it works perfectly after I swapped the green and grey wires from his instructions after testing everything. (The high- and low-speed fans were reversed.) One of the tricks in addition to the relays was to make sure to train the Nest what gets hooked up to Y2 since it’s a two-speed fan not “Stage 2 cooling”. Thanks to Rick for the great tutorial.