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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I need a C wire new thermostat. My furnace has a /C

Customer Question

I need a C wire for my new thermostat. My furnace has a B/C terminal which currently has the Y wire attached to it, even though there is also a Y terminal on the furnace. There is a black wire and grey wire that are unused, but neither of them seem to have power when connected to the B/C terminal. Any ideas?
Submitted: 2 years ago.
Category: HVAC
Expert:  gotoman for ac replied 2 years ago.
If you will look you may have one of the yellow wires from outside unit attached. Just attach one of the wires not used black or grey and attach at furnace to b/c and C on thermostat. Russ
Customer: replied 2 years ago.
I don't have a yellow wire. I'll include some pictures. You can see the two unused wires, but the thermostat still doesn't power on when I use either of them and plug them into the B/C terminal on the furnace and the C input on the thermostat.
Expert:  gotoman for ac replied 2 years ago.
Check furnace board for fuse. It may be blown. Do you have a red light on furnace board. Remember door switch has to be pushed in for power to furnace. Russ
Customer: replied 2 years ago.
Good point. I checked the board and don't see any red lights. However, if the fuse were blown, wouldn't that mean the current wire in the B/C slot would not work?

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