My York A/C unit is not turning on inside or outside. I changed the batteries in the thermostat without luck. This unit is 5 years old. What could it be?

Have you checked the breakers yet? Every couple years mine trips them for an unknown reason , and once I reset them all is fine for another couple years.

I have not. I was worried about resetting them because I didn't want to mess up the upstairs A/C unit (which is working). One is labeled A and one is labeled B, I wasn't sure which is which. I am assuming A is the downstairs one though. Do you think I should try that before calling the A/C guy out?

Yes... it might save you the cost of a service call. Worst case you are still calling him. Turn it off, wait a minute then turn them back on. It's a longshot it would be the same as I've seen, but its free to try.

Thanks, I'll give it a try.

Didn't work :(

Well, it was worth a shot.

Yeah, thanks for your help. Had an AC guy come out. AC works, but electricity isn't getting to the unit in the attic, I'm not sure what it's called, the furnace maybe? So now it is working with an extension cord running from my attic space to the socket in the hall. Quite classy! Apparently I need to call an electrician now. Oh and I'll need to replace the motors on the AC units fairly shortly too...

Thanks for the update. I'm surprised you got someone that quick.

It was nice to get someone quick. We had hired this guy to move our AC units a few years ago, so I just called him.