Air Conditioning - still no a/c, but heat comes on

OK. when the thermostat is set to "auto" and "cool", and the temp selector is below room temp, nothing happens at all -- no blower kicking on, no outside unit kicking on, nothing except the transformer blowing after a few minutes. there is power to the system. on "auto" and "heat", the blower comes on and the heater works fine. blower fan works fine by itself on "on", also.

I tested the 24v line from the inside through to the compressor unit outside and have continuity all the way through the relay coil outside and back, so it doesn't look like a short there. I manually pushed down the relay and the outside unit kicked on.

I changed the thermostat, same thing.

could this be a problem with the circuit board? of the two 24v lines heading out to the compressor unit, one comes directly from the thermostat, the other comes not from the transformer or thermostat directly, but from the circuit board.

how can I figure this out?

it's a goodman system.

any other suggestions? thanks again for the advice so far.

In my house i also found that one 24VAC "hot" line comes to relay/contactor outside directly from the thermostat, and another 24VAC "neutral" line come to outside relay from "C" terminal on the board. In my case, the outside relay/contactor measured 11 Ohms resistance, if yours is less it might short the transformer.

Also the transformer must be rated appropriately to handle this much power: 24 VAC/11 Ohms = at least 2.2 Amp. but more likely 3 amp.

If you are buying the 24 VAC transformer for a door bell use it may not be rated to carry such load.

Another way to test would be : remove transformer, take it outside to AC unit, connect 110 VAC to it, and connect 24VAC output to relay/contactor and see what happens -if it blows then either relay is not good, or transformer was not good.

The transformer is a 240/24vac, 40va. purchased from an a/c parts shop, matches the original.

the relay coil on the outside unit seems fine on the meter.
also, even if the outside relay coil was bad, shouldn't the blower fan still start up and run?

assuming that the outside relay coil is good, what else do I need to look at doing?


thanks for the help.

The transformer is a 240/24vac, 40va. purchased from an a/c parts shop, matches the original...



40 Watts/24VAC = 1.7 Amp


I' d try a more powerful transformer, w/ a 3 amp fuse in-line so it would not blow.
Why the transformer is 240 volts?
Is you furnace working from 240 VAC ?