I'm new to putting in a thermostat or working on anything like this, so please bear with me. I really appreciate any help you can give me with my problems. Ok, I have a thermostat that has only three wires attached to it. It has a red wire, a black wire, and a white wire. I have no clue ehat these wires are for, but these wires control the air conditioning of my house only. I have a separate thermostat for the oil heating in the house. Can anyone expain what each of these wires do? Also, what kind of thermostat do I need to replace the old one with? I tried a new honeywell, but the wiring is labeled by the function of the wire (heat, cool, Fan 1, Fan 2, fan 3, etc), not color of the wire (R,Y,G,B, etc.).

I am guessing that the red wire is your power coming from the transformer. The black wire is just a guess. What you could do is put a jumber across the red and the black wire and find our what it does. It may turn on your condensing unit and the air handler. Then do the same thing with the red and the white. It may turn on the air handler only. If what I have said is correct then you can use a four wire thermostat. This si the way you would wire it. Put the red wire (if in fact it is the power wire) on the screw marked with a R. Then put the black wire on the screw marked C or cool. Put the white wire on the screw marked G or fan. Do not connect any wire to the screw that is marked W.

Can a aircondition thermostat be wired to 110 V or does it have to be wired with 24 v
Glenn