How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask BillyHvac Your Own Question
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22541
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
Type Your HVAC Question Here...
BillyHvac is online now
A new question is answered every 9 seconds

I have a Carrier 8000VS model 58CVA070-12 gas furnace. I neglected

This answer was rated:

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?

My name is Billy.

Do you have a voltmeter?


Customer: replied 3 years ago.



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.


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!


BillyHvac and other HVAC Specialists are ready to help you