Air Conditioning - transformers pop, heater works, but a/c won't

I'm stuck. I have an a/c system with electric heat. air handler inside, compressor outside. ran the a/c a couple weeks ago with no problem, cooled just fine.

last weekend I put on just the inside blower (thermostat was set to "cool" and "on", not "auto") to move some air around the house. after a while I noticed the fan wasn't running. tried "auto" on both "cool" and "heat", nothing worked. pulled the cover off the air handler and the transformer read 0v on the low side. replaced the transformer, got 24v. set thermostat to "heat" and "auto", heat worked right away. switched it to "cool", slid the temp selector down below room temp, but nothing happened.

I changed the thermostat to see if the problem was there, and the same thing happened. heat, but no cool.

it gets better. I left the thermostat on "auto", "cool", and with the temp selector below room temperature for abit to see if the a/c would kick on. after about 1 minute, the new transformer popped and went out.

what should I check next? I'm thinking it's not related to the compressor unit outside, as I didn't have it on when the first transformer blew, just the inside blower fan. Or am I wrong? Help, please!

It sounds like a shorted wire to the condensing unit (outside unit). Since it is only energized on call for cooling.

It may not be a bad idea to wire in a fuse at the low voltage side of the transformer so you don't burn out its replacement.

Thanks for the tip. So when I test the 24v line leading out to the compressor unit, should it show on the voltmeter as if it were a closed circuit? My guess is it should, as 24v goes out one line, through the relay coil out there, then back in through the other line. Or did I miss it?

Thanks for the tip. So when I test the 24v line leading out to the compressor unit, should it show on the voltmeter as if it were a closed circuit? My guess is it should, as 24v goes out one line, through the relay coil out there, then back in through the other line. Or did I miss it?

I just tested my AC contactor (relay) - it was 11 OHm, yours should be somewhat close to that number.

On the outside unit there is a service "door" which allows to look/check the wiring before it goes to compressor and fan motor-see if the contactor/relay is not shorted.

OK. I tested the line from the inside through to the compressor unit outside and have continuity all the way through the relay coil outside. I manually pushed down the relay and the outside unit kicked on.

In case I wasn't clear earlier, 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. But on "auto" and "heat", the blower comes on and the heater works fine.

The fan works on "on". the only thing that does not work is "auto" and "cool", and I blew 2 transformers doing that.

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 (if I remember correctly), 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.