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BillyHvac
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22092
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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I have a Carrier 8000VS model 58CVA070-12 gas furnace. I neglected

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I have a Carrier 8000VS model 58CVA070-12 gas furnace. I neglected to turn off power to the furnace and AC when I disconnected and reconnected the thermostat (remodeling).

Now the thermostat has a blank display. There is no 24VAC to the thermostat. No voltage where 24 VAC leads from air handler transformer connect to block on board. Fuse on board is okay.

Can this be anything other than the air handler transformer? Anything else I should test?
Hello,

My name is Billy.

Do you have a voltmeter?

Billy

Customer: replied 3 years ago.

yes


 

Tape door safety switch down securely.

Turn power on.

Test terminals SEC1 and SEC 2 on the board. Tell me if 24v present there.

Customer: replied 3 years ago.

27.2VAC

Thank you.

Now R to C

Not to bore you but a step at a time helps because I never know what direction the next step takes.

Do we have 24v R to C?

Customer: replied 3 years ago.

Still no voltage between R & C

Pull the fuse out....measure across the fuse receivers...

Customer: replied 3 years ago.

Ah Ha! 27.2 VAC. When I tapped fuse. Where it appeared to be okay before - now can see it is obviously blown.

Excellent...that was the last test to see if fuse or circuit board.

I am glad it was 5 cent fix instead $200.

Thanks for your meter and skill to use one. It really makes this easier!

Billy

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