Thermostat digital display blank after severe storm

Problems related to residential installations.

Thermostat digital display blank after severe storm

Postby R3V0 3VOM » Sun Jul 03, 2011 3:30 pm

After a severe storm yesterday, I came home to my thermostat's digital display being completely blank and the a/c not running. Somehow it's tied in with my home alarm keypad, as the alarm no longer chimes whenever a door is opened (and an "AC" indicator is appearing on the display). I've checked the thermostat (Robertshaw model 9401), and it's power source is from the house (no batteries). My assumption (which is up for debate) is that I had a power surge that fried the thermostat. I've flipped the breakers, turned the "light switch" in the garage that's designated for the compressor/air handler off and on...but no luck thus far. Any thoughts as to what else I can do to determine the root cause? And if not, any recommendation on whether I should call an electrician or an HVAC tech?
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- Thermostat digital display blank after severe storm

Postby R3V0 3VOM » Sun Jul 03, 2011 8:52 pm

Thanks for the reply. I checked the circuit board, and I'm seeing one purple fuse with an "E" on it, that looks similar to a car fuse...I'm assuming that's the one you're referring to...it looks intact to me.

I guess the next step is to look at the transformers. When you say transformers, are you referring to the fuses in the breaker box?

Thanks in advance for the clarification!
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- Thermostat digital display blank after severe storm

Postby R3V0 3VOM » Sun Jul 03, 2011 10:41 pm

LOL! I was wondering what the hell an E was doing on a fuse...I turned it around so it now reads "3". Wish I could use the blonde excuse for that one...

Anyway, yea...I pulled it out and it's intact.

Looks like this is the extent of my diy, since I don't have a volt meter. Any recommendation of where to buy these transformers, in the event that's what the problem is? I have a contract with an HVAC company that I pay a monthly payment to, but honestly, they're a rip off (charged me $300 to spend 20 minutes to replace a $60 part before) so I'll probably have them troubleshoot it, but handle the repair and/or find the part myself.
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- Thermostat digital display blank after severe storm

Postby R3V0 3VOM » Mon Jul 04, 2011 11:33 pm

Transformer turned out okay. It ended up being the thermostat. Not sure if the circuit board in the thermostat got fried somehow, but once I replaced it, all was good.
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