Replaced board in condenser - now thermostat burns up

9 years ago

We have a heat pump HVAC system that had the condenser unit stop working - the fan would blow inside but no A/C. The tech said the board in the unit (outside) was bad and replaced it. He also said a wire in there was bad and replaced. It worked when he was here, but I turned it off because we didn't need it. A few days later nothing is working and a "burn" spot shows up on the display of our thermostat LCD. I took it off the wall and can clearly see it got fried by receiving too much electricity. (see pic) it's only supposed to get low voltage and it apparently got 120V.

Here's the thing - he's coming back Monday but tried to say over the phone that there is no way what he did could cause this type of (high) voltage to melt the thermostat so it has to be something else. I don't believe it since it was clearly connected to this "repair" job.

Can any expert comment as to if/if not tinkering incorrectly around in the condenser electronics can cause other problems down the lines such as this. We are not liking the idea of being tricked into paying for damage he might have caused in the first repair process.

Thanks in advance for any input!

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Comments (6)

klem1
9 years ago
Well I would say you are on the right track but confirming it is next to impossible unless you are trained in electronics. It doesn't require 120 volts,enough wattage in 24 volts can do damage shown. Low voltage is commonly but not always fused to prevent the type damage shown. My best guess is that a short occured ( bad wire that was replaced) shutting the unit down . That may or may not have damaged the circuit board and/or t-stat but should be confirmed before replacing board and/or putting system back in service. Once again,only a hunch but said fuse might have been bypassed if it was present to begain with. Non of this is rocket since "IF" one is compitent in using a volt-ohm meter,which every tech should be.
karyn
Original Author
9 years ago
Thanks for the reply, we'll see what he finds today!
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karyn
Original Author
9 years ago
Hmmmm strange - today he says there is no freon in it at all. Didn't fix the wiring issue yet however - coming back again tomorrow.
klem1
9 years ago
"today he says there is no freon in it at all."

In case you are wondering,that is simple for a tech to 100% confirm regardless of other problems. Were you my best friend or mother I would tell you I'm on the way over or sending someone to get to the bottom of it.
mike_home
9 years ago
From what I have read and seen so far I have no confidence in this tech. I hope this gets resolved.
karyn
Original Author
9 years ago
He did a test overnight - to put 100lbs PSI of nitrogen into the system to see if it held. It dropped to 30PSI overnight so there's clearly a leak though nothing visible (no oil etc.).

A new thermostat is on now and seems to be working fine so finding the leak is the next step but we don't need A/C and the heat is working which is good.