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Help! I replaced my main Dometic air conditioner. No problems at all, works great. It had a 7-wire thermostat. I replaced it with a Dometic 3-wire thermostat. Married up the wires, all simple enough, and as I said works great. BUT. My Atwood furnace also worked through the thermostat. After wiring up the a/c and new thermostat, which was all labeled and a no-brainer, I had 2 white wires and 2 orange wires left over. These are heavy wires, not thermostat wires. I have 2 terminals on the control box that say “furnace.” Where do I go from here?

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When you have a thermostat which controls both the a/c and the furnace, it does so by sending all of it's outputs to a control circuit board inside of the a/c unit and that in turn controls the furnace, via the two thermostat leads from the furnace. Those two leads are just a 12V signal that is either open(not calling for heat) or closed(calling for heat). Since your RV was wired to use a single thermostat for both, the furnace thermostat leads probably do not go close to the existing thermostat. By eliminating the a/c control circuitry, you don't have a thermostat for the furnace and now need one.


I don't know for sure what your extra leads would be but would need to know which thermostat you had to figure that out.

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If you installed the new style control box that is gray then the furnace wires go into the side of the control box. if you look on the side on the control box toy will see where two male spades are located. They are for the furnace wires. It owes not matter which goes where, just plug them in.

But first you need to determine what wires are for the furnace. The simplest way it to look for a small two stranded wire coming into the A/C area. They may be connected to heavier wires once inside the opening.

The other quick thing to do is to touch two wires together that are paired together. If the furnace comes on they are the furnace wires, if not then try the next pair.

Maybe best to go to the furnace and locate what wires are connected to the blue furnace wires then find them in the control box area.




Safe Trvaels, Vern

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