I combined 2 old separate thermostats for totally separate systems into one Hunter thermastat. One was for a propane forced air heater and one is an A/C system. Everything in summer seemed fine. Now with the heater running, warm air is coming out of my A/C's return air vent. I can't understand that at all. They do use the same vents, but separate returns. Is one of my wires in the wrong place? Thanks!