Furnace and AC won't function

[Montrealer]

My neighbor has a 2007 Mallard travel trailer with a gas furnace and a roof mounted 120v AC unit. Both are controlled by the same thermostat. Thermostat has 6 wires, 4 to the AC and the other 2 to the furnace. I verified all fuses and breakers and all is in order. Verified current to the thermostat and there is 12 v present. Even tried a new thermostat to no avail...... Thoughts?

[HoboPals]

Don't know if this will help-it's just a thought, but I had a bad fuse last year and replaced it with a brand new one. Someone double checked that I had put it in correctly and other things and he had no answer other than I needed to get to an RV repair shop. I asked him if it were possible that the new fuse was bad and he said it was highly unlikely. In the middle of the night, I woke up and the thought went whizzing through my brain, "Highly unlikely means may be possible."

I got out of bed, got another new fuse and plugged it in. Voila--fridge, etc. went on.

[Paul R. Haller]

In my coach both the AC and the heater work with +12 volts DC to manage the systems in the printed circuit boards. If your batteries are weak and +12 volts DC is say 10.5 volts... it doesn't work. Also check the circuit boards in the heater and AC unit and check for corrosion. Sometimes all it takes is a pencil eraser or even taking off the connectors and reinstalling them to clean the connections.
-Paul R. Haller-

[TXiceman]

Check the voltage to the controller board first. Next it may be a bad board in the A/c unit.

Ken

[Montrealer]

Thanks for the ideas guys, and will definitely give them a whirl.

Checked voltage to the thermostat controller board and it was 13.4v. The fact that both the furnace and AC stopped working pointed me to suspect the thermostat controller board as the culprit. Changed the small 2amp fuse that is part of the board. Event went and bought a new board and connected it. Still not working. I'll report back after trying your suggestions.

Tanks again.