AC

[Bobcat1]

We recently purchased a 2008 Jayco Melbourne. We cannot seem to get the AC nor furnace to operate. The thermostat doesn’t show any numbers/readout. Otherwise everything else seems to operate appropriately.

Please advise.

Thank you.

[Grumpy]

There is a fuse in the thermostat. Also check the main furnace fuse.

[Bobcat1]

Thank you for your response. The fuse looks fine. Would the fuse in the furnace affect the AC?

[JimD]

The thermostat is the only common factor with the furnace and ac. Nothing in the furnace would affect operation of the ac and visa versa.

For furnace operation the thermostat simply puts 12 volts on a wire going to the furnace. The furnace will then fire up. It will stay active as long as 12 volts is being fed from the thermostat.

The ac operates much the same. 12 volts on a wire from the thermostat will turn the ac on. There is also an additional feed to the ac to select low or high fan speed.

So, in your case I would suspect that either the thermostat is bad or has a blown fuse or it is not being fed with 12 volts. You could easily measure the 12 volts on the back of the thermostat with a voltmeter (everyone should have a cheap voltmeter). No dangerous voltages here. If no 12 volts, the problem is hopefully just a fuse blown in the coach fuse block.

If you have 12 volts at the B and R terminals the problem is the thermostat. You could jumper the positive 12 volts (R) to either the W or Y connections and the furnace or ac would start up. A pair of needle nose pliers works great for this. This is all the thermostat does. It has little relays that just connect the wires together.

I have included a typical wiring diagram for a thermostat. The wire colors may or may not be accurate! It all depends on what Jayco decided to use. I would ignore the wire colors and just go by the labelled terminal connections. All thermostats will have the letter code for each terminal connection.