Finished a new upgrade.
Installed a Honeywell residential thermostat I had lying around. The benefit is a digital temperature reading and a digital setpoint. For A/C, it won't run the fan constantly, only when needed for cooling. And my wife cannot reach the knobs on the ceiling unit, now she can control the A/C just as you would at home.
I couldn't find any writeups I liked, so after lots of testing with a multimeter, I worked this out:
Furnace:
*My thermostat is a battery powered type. If the thermostat is looking for 24vac to power itself, it will not work for rv applications. "millivolt" on the thermostat paperwork, should mean it's capable of switching 12v triggers for RV hvac*
I started by using my inexpensive Honeywell it as a direct replacement for the 2 wire mechanical furnace thermostat. + (Red) to R and furnace relay (white) to W.
A/C:
I then researched controlling the A/C with the thermostat as well. I've seen many that install a relay on the 120v line for the A/C and have the thermostat control that relay, but I wanted the control to be more specific than that - fan and compressor. I also wanted to eliminate the surface control.
The A/C controls on my unit are very simple. I replaced the multi function knob in the control box on the ceiling assembly with 2 12v coil 120v 30a relays (one for high fan and the other for compressor). I may go back and worry about low fan another time. I also ignored the wire for a heater.
I then replaced my 2 wire furnace thermostat cable with some 18/7 thermostat wire to give me plenty of conductors. I had to run it under the trailer which was a chore on its own. I ran this to the furnace and then up to the A/C. Furnace thermostat wiring was unchanged to add A/C other than using the wires in the new cable.
A/C wiring at the thermostat was Y, G and RC ( I removed the thermostat jumper). RC is a 12v source with a 1a fuse. Y is the new compressor relay and G is the new high fan relay. The relays need grounding, so I used a wire in the cable as ground.
Fully tested and everything is working perfectly.
I didn't go into any detail on pulling the thermostat wire as every trailer is different and wouldn't resonate unless you have a 2017 267bhsw.
If I can think of something to take a picture of, I will. I drew a wiring diagram, I'll find that.
Here are the relays:
https://a.co/d/cJxRFyu
I did not use the provided wires for the 120v side. They are too thin. The 12v side doesn't matter as I measured the coils at .07A each.