Originally Posted by javelin
On basic RV thermostats usually the wiring terminals are labelled. The Y terminal should be connected to the air conditioner control relay in the ceiling plenum (call for cooling); the W terminal should be connected to the furnace (call for heat). Sounds like the two wires are reversed? Note the G terminal usually controls the fan speed for the air conditioner and typically connects through a fan speed switch to connect to either a low or high speed control wire up to the air conditioning controls in the ceiling plenum. Did someone do the analog to digital thermo conversion recently?
If this is a problem with a new coach (only 5 Posts and he doesn’t say) it could also be those wires are switched at the A/C controller. Since Thor does not seem to always use continuous wires from the thermostat to the controller, it is easy to mix up the wires at the controller if they used different color splice wires,