No power to thermostat

[LuckyJones]

2021 JAYCO 24Bh - taken 3 trips with no issues. Pull up for our 4th trip and the AC wouldn’t turn on. All other power works. All fuses and circuit breakers are intact and working properly. We know that the 12v on the ceiling is not getting power to run the thermostat. Where do we go from here? Is there a simple fix? We are burning up in North Georgia!

[mini4mw]

all the other 12v lights and such work fine i assume?
is the thermostat on the AC in the ceiling or is it a separate unit on the wall?
if its on the wall, is it analog - old slider thermostat, or digital?
nothing works from the thermostat - fan or AC?

I believe the thermostat gets the power from the control box. The control box is above in the incoming air. Inside the RV, take down the plastic covers/vents and you should see it inside near the front of the AC unit on the roof. Check all the wires are secure. May want to unplug/turn on battery disconnect. Don't want a shock from there.

I'm not sure if the control box takes the 120v in and then sends 12v to thermostat or if there is a different 12v lead from the battery to the control box to the thermostat or if it bypasses control box entirely. Attached is a picture of what to look for. You don't have to take everything off the ceiling. You should be able to reach up through the holes once the cheap air filters are off.

[Grumpy]

The 12v for the thermostat does not come from the a/c unit, it is fed from the fuse panel. There is also an internal fuse in the thermo, and there may also be an inline fuse in the wiring bundle in the wall behind it. You need to remove the thermostat and pull the wires out of the wall. Some thermostats also get their 12v power from the furnace circuit so check that fuse too.

[JimD]

Some thermostats receive the 12 volt supply from the furnace rather than the fuse box. I think mine is that way. Check the power to the furnace. Fuse would be first check.

If the furnace works but the AC doesn't, the thermostat is receiving power. In that case you may not be getting 120 volts to the AC. Tripped breaker and other problems can cause that.