I have a Rheem Critition heater/air conditioner not powering up. I have 110 to the power control board. Had a transformer go bad a bit over a month ago. The transformer is not putting out 24 volts, but both primary and secondary sides of the transformer are not open. I thought it needed a new control board at that point so replaced it. Still doesn't power up.

Anyone have any ideas? This is my upstairs unit and I'm the only one that goes up there much.

You answered your own question.

If the transformer has 110 going in and 0 coming out you need a transformer. Buy one with the same VA rating and get one with a circuit breaker built in

I put a second transformer in, I have another because they are so cheap. Local place sells them for $11, so it is worth keeping a spare around. I'll throw the extra one in tomorrow morning and let you know.

I checked this afternoon, had 120 V at the terminals from the board. So I took a new transformer and wired it directly into the terminals on the 120 V power and on 24 V control, turned it on and it started working. Went through 3 transformers, I'll see how long this one lasts.

Tested it for a bit last night, blower motor on all the time, A/C unit doesn't turn on and thermostat does not control anything.

Check for any fuses on the board.

Found a blown 3 amp fuse, one of the wires to the t'stat was slightly loose tightened it and replaced the fuse. Been good the last 2 days