Air Conditioning - A/C not turning on after thunderstorm.

My mother-in-law's A/C stopped working after a lightning struck a nearby transformer. She had her boyfriend change her old school thermostat for a newer programmable one. They check the breaker boxes both inside and outside and made sure they weren't tripped. Still didn't work.

I came over and took off the cover on the outside unit. The contactor looked like it blew out. I replace it with a new one (wire for wire). I check to make sure all connections on the new thermostat were hooked up right and turned it on. Still no luck. I took a voltmeter and checked the outside breaker A/C relay, power lines before the contactor, power in between the contactor and all showed 240v. I checked the smaller wires that hook up the the sides (thermostat wires?) and didn't get any reading.

Inside fan, outside fan and compressor not turning on. The power isn't tripping the contactor. I don't know if I was supposed to do this but I manually pressed the button on the contactor and the outside fan and compressor turned on. But my wife said the inside fan didn't.

I don't have much knowledge about this stuff, so any ideas?

The thermostat which controls the power to the relay in the outdoor unit gets its power from the furnace.
This is where you need to check.
The breaker to the furnace could have tripped or the lightning could have taken out a cct board if it has one.

So if that cct board is fried then the indoor blower fan won't turn on? Or give the thermostat the ok to send power to the outside relay (contactor)? I'll see about that, but it won't be until Monday 'til I could get parts.

All the breaker switches are on the on position.



BTW, What does "cct" stand for?

You dont say what you have under that AC a furnace or just a blower coil under it Can be a board there. With a transformer and blower relay. You have to check and see if,are do you have 24V power there. Some furnace boards have a small fuse on them. Check for that you need it to go to the tstat to power back to the AC and blower inside.

check the secondary of the transformer for 24 volts

Sorry, cct is an abbreviation for circuit.

It's a furnace. I'll check it out for any more relays, fuses, or transformers. I'm just trying to save my Mother-in-law from getting her eyes poked. It seems like alot of big name a/c companies here like to suggest changing out your entire system even when all you need to do is something little.

More info:

Magic Chef Forced Air Furnace
Model #G66-75D2C25-6
Serial #I 02540EEB
1983

I Checked the outlet that it's plugged into and it check out @ 124v.
There's a transformer that sits on top of a box that the main power goes to. I recognize the wires that are hooked up to the transformer are coming from the thermostat. There are other wires connected to it too. I just don't know which ones to test for voltage/current and see if the transformer is bad. I'll try to find something online for illustration purposes. I don't have my digicam with me right now, so I can't pic and post it up.

At the furnace you want to take a reading between R and C on the t-stat wire connections.

You may have a door switch that needs to be pressed to have power.

Ok, at the furnace I checked for voltage at the transformer between R and C. I came up with "0". I re-checked the voltage where the it's plugged in (elec. outlet) and I'm getting roughly 124v. So I'm getting power to it, but not on the other end. Time to replace that part, or is there another part to check?

BTW, there was a door switch and I made sure it was closed.

Go to the transformer itself, and check the power going in and out of it.. If you got 120 going to it, and nothing out, then transformer needs to be replaced.

If you are getting 24 at the transformer, then look for a fuse or mini breaker on the low voltage side.