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BillyHvac
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22508
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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no power to the thermostat inside. Where is the 24v transforner

Customer Question

no power to the thermostat inside. Where is the 24v transforner and how can I field test it? also there is a loose wire with a female connectoe coming from t1 on the printed circuit board, any ideas where this might go?
Submitted: 6 years ago.
Category: HVAC
Expert:  Tom replied 6 years ago.
Chat Conversation Started
Tom :

Hi sorry you're having trouble. What model of furnace do you have? Perhaps I can locate a diagram for it. The transformer is probably on the control board depending on the age of your unit. I'm wondering if the wire from T1 might be line supply and you're not getting 120 volts to the board. Let me know about the model and I'll see if I can help. Tom

Tom :

Has any work been done on the unit recently that might account for the loose wire?

Customer:

no, none. I have a frigidaire T3BC 042K

Tom :

Ok...I have no records on Frigidaire ...sorry. Is the loose wire attached at T1 on the board and then is just hanging loose?

Tom :

If you have a volt meter you can check the low voltage terminal strip where the thermostat wires connect. You should have 24 volts between R and C.

Tom :

Also I would follow the 120 volt supply ... should be a white and black... to verify line voltage on the board. Perhaps the T1 and a N (neutral) terminal. The neutral strip will probably have several white wires on it.

Tom :

Double check to see if your furnace has a door safety switch..if so you'll have to hold it or tape it down while checking power.

Customer:

yes a yellow wire attached to T1 on the pronted circuit board. It looks like a small jumper wire but not connected to anything. I'll go check R and C volts now. Any idea where I would find the transformer?

Tom :

It is probably right on the circuit board. If you check R and C you will be checking the 24 volt secondary side of the transformer.

Customer:

no power between r and c. Is the transformer one of those black blocks on the board that reads 24v?

Tom :

The black blocks are generally relays for the fan motors.

Customer:

ok, well I think I have a bad transformer. How would I find it

Tom :

See full size image

Tom :

Here is a picture of a typical Lennox board...

Tom :

The transformer is in the upper right hand corner..the white object.

Tom :

Does that help at all?

Tom :

Did you verify 120- volts supply to the board?

Tom :

Also most newer boards (not all) have a fuse to protect the 24 volt circuit. If your board has a fuse on it..pull it and make sure it is OK.

Customer:

My board looks nothing like that.

Tom :

Ok...sorry I can't be of more help. I will opt out and hopefully one of the other tech's might be more familiar with your Frigidaire unit. Tom


 


 

Expert:  BillyHvac replied 6 years ago.

 

Hello,

 

do you still need assistance?