A/C repair question

Factual Questions
1

The repair guy just informed me the circuit board in my home air conditioner/heater unit is fried. I was up there a few days ago trying to figure out what the problem was, and the circuit board flashed a pulsing green signal that meant “operating normally” according to the circuit board schematics.

The unit will blow the fan if neither “cool” nor “heat” are selected. If you select either cool or heat, the fan will stop blowing, there is a buzzing sound that normally means the unit is warming up and will turn on the fan shortly, but after a few moments the buzzing stops and the unit shuts off.

I have a feeling the repair guy is full of shit, but since I don’t actually know what’s wrong I’m forced to pay whatever he tells me to. Can anyone confirm my suspicion, or explain why I shouldn’t be suspicious about it?

2

I just helped a friend diagnose and repair a similar problem over the phone from hundreds of miles away.

Different manufacturers have different boards and different ways to control the unit. It may be very hard to diagnose this in a MB format.

I’m not sure that I can correctly diagnose the problem with only the telephone and your input, but I do have experience with these things.

If you wish to PM me, I’d be glad to give you my phone number. If not, feel free to post here:

Manufacturer & model number

But the phone thing might be easier…

3

I appreciate the offer. I’ll give you a PM and also get the manufacturer and model of the unit tomorrow. I have to leave for work now. Thanks!

4

The LED flashes a fault code to direct the tech to the source of the problem.

If you turn the 120V off, however, the LED resets the fault. That’s why most furnaces that use LED codes put a small Plexiglas window on the door so you don’t need to take the door off to see the code. Because if you take the door off…you guessed it; you reset the code by interrupting the 120V.

So…see if the fault reappears. Just don’t take the door off to find out.

Goodman and Bryant had boards that solder joints would “break” after time. It would manifest itself by allowing the small blower (the ‘draft inducer’) to come on for just a second or two. The connection was good enough to produce “ghost voltage”; voltage that would appear on your meter, but would not stand up to a load. So…when there was a call for heat it would only be able to start the fan and then the loose solder connection would “drop out” the voltage.