[aj5150]

What causes the furnace and the ac to come on at the same time

[Joshdta]

Wire touching either at the furnace or the t-stat

[aj5150]

Reply I could not find any touching wires I looked for that too

[aj5150]

Thought maybe the relay has gone bad

[Joshdta]

Could be the control board, or the t-stat. take the stat off the wall and jumper r to y and see if just the ac comes on or both

[Joshdta]

Is this a electric furnace?

[aj5150]

This is a gas furnace and I disconnected the white wire from the control board and had friend turn unit back on and no heat just ac

[Joshdta]

OK, but you need to do this at the t-stat to see if the stat has gone bad.

[aj5150]

I could do a continuity test on the wires though if I unhook from both control board and t-stat

[Joshdta]

Yes you can also do that as well

[aj5150]

I will unhook from t-stat and see if that is not the problem do you think that the wires could have chaffed together

[Joshdta]

Maybe, or the subbase on the stat just went bad. Is it a digital one or a old mercery one?

[aj5150]

I did have that problem once before on a unit I was working on at work where the wire had chaffed togetherI also have another a/c doing the same thing where both come on at the same time

[aj5150]

Well it's a new mercury one but yeah same difference