Big storm today, lightning strike in the back yard. Tripped the main breaker (the one next to the meter).

Got everything restored, everything in the house working now, except the air conditioning. The display on the thermostat remains blank. Tried all the troubleshooting steps that I could find, no joy.

Any suggestions?

Does the fan on the unit spin? If not, it it likely the start capacitor has died.

My air conditioner has its own breaker outside by the unit. Does yours?

quote:

Originally posted by Anush:

My air conditioner has its own breaker.

Mine too, in the breaker box in the garage. The one that was tripped by the lightning strike is the main one adjacent to the meter, the one that feeds the breaker box.

quote:

Originally posted by Lunasee:

Does the fan on the unit spin? If not, it it likely the start capacitor has died.

That's not the problem. The thermostat display is totally blank. Thermostat won't come on, won't call for the system to power up.

Did you replace the batts in the thermostat?

Doesn’t the thermostat receive power from the heater board? Then a call signal is sent to the compressor? So one should check the heater board first?

I am not sure what type of system you may have but check the breaker at the air handler maybe in the attic or wherever it may be. That normally powers the low voltage transformer in there that feeds power to the Thermostat and if that breaker is good, possibly transformer burned or fuse on control board may be blown.

quote:

Originally posted by Mustang-PaPa:

Did you replace the batts in the thermostat?

No batteries in this model.

More than likely a blown fuse or transformer in the indoor coil unit.

quote:

Originally posted by PowerSurge:
More than likely a blown fuse or transformer in the indoor coil unit.

This happened to one of my units once. After calling a technician out, he used a simple automotive style fuse to replace the burned out one on the air handler upstairs.

Pull the cover off the thermostat and check for 24v across R and C (Red/power and Black/common) common might be blue.

The point is to check the wires to those letters. R, C, to check power from the transformer (and power to the handler).

If you have power with a meter, the thermoset is likely toast.

While there, connect R (red wire) Power, Yellow (yellow wire) Compressor, and G (green) Air Handler Fan.

You will get Air.

If all that works, you can replace you Thermostat (take yours to the big box store to make sure you get the correct one.)

If you have power from the first step, but the second step only the Compressor and it's fan comes on, but the air handler fan does not, it is either a fuse on the system board, or the board may have failed on the controller on the board.

But you will have a better idea by those two tests, and hopefully it's just the thermostaat.

Take picture of the current pinout to wiring and notice the colors and map them Color to Letter, for later.

You may have other wires for staged systems, but the R,Y,G will give you low speed if it is a staged system, or "normal" AC if it is not.

Make an model of the air handler?

quote:

Originally posted by sigmonkey:

Make an model of the air handler?

Thanks for the trouble-shooting steps; I'll do them later after I deal with a few other problems. Looks like the power surge took the garage door opener out of service, too. Other things pop up as we try to use various devices.

Re make and model, the system is Goodman; I'll look for a label with model number in a bit, after I put out couple other fires.

There is a small auto style fuse on the mother board of the unit. I accidentally fried it once and had the same symptoms. Just before calling the tech I noticed the fuse and replaced it. Fixed the problem.

quote:

Originally posted by jeffxjet:
There is a small auto style fuse on the mother board of the unit. I accidentally fried it once and had the same symptoms.

There is a fuse inside the thermostat?

On the motherboard of the main air handler unit, which is likely in your attic.

It protects the low voltage circuit that powers the thermostat.

The board will be under an access panel or removable body panel on the main unit, and will look something like this, with an automotive-style blade fuse with the amperage printed on top. (Usually 3A or 5A)

Shut power off to the unit, replace the fuse with the same rated fuse either from the spare fuses in your car or from the auto parts store, then power it back on and see if that corrects your issue. If it blows again, you have deeper issues, like a wiring short.

The two things that have blanked the thermostat for me are:

1. Circuit breaker inside the air handler. Just a press of a reset button, but I see from reading this thread others have a fuse.

2. Much more common, the condensate drain line is clogged and trips the float switch.

Given the lightning, #1 seems likely. #2 is an easy check though, just pull the float switch out of the drain line, stick your finger in where the float switch was and see if it’s full of water.

That's rough, especially this time of year, think I'd just call an AC company and get them out to check it out and fix it while you deal with all the other stuff.

Your HO insurance may cover the repairs, so if you need new garage door opener, an handler etc keep everything totaled up, as long as it exceeds the deductible.

If you'll be down a while you can pickup a window or floor AC unit at Lowes to put in the master...

quote:

Originally posted by V-Tail:

quote:

Originally posted by jeffxjet:
There is a small auto style fuse on the mother board of the unit. I accidentally fried it once and had the same symptoms.

There is a fuse inside the thermostat?

Rogue got it. The motherboard on the main unit.

quote:

2. Much more common, the condensate drain line is clogged and trips the float switch.

Definitely check this. I've seen it personally. And my T-stat was also blank.