I've moved into this house with what looks like a fairly new unit outside. The air conditioning runs perfect but on the first cool night I tried turning on the heat and it does not kick on. I used the thermostat to switch to on and there is nothing but cold air blowing from the vents. The model number is PY1PNB090ABAA. I need to know what to do. Any help would be greatly appreciated. I do have some knowledge on units but none on a Payne system. Never dealt with a combined unit that is outside. Thank you.