furnace
I have a blue wire being unused on both the furnace and thermostat. If I connect that blue wire on both ends will I have power?
Page one of the wiring diagram:
Page two of the wiring diagram:
What it looks like at the thermostat:
How it looks at the furnace:
Since in your case, one side of the transformer is grounded. You can simply use a fork or ring terminal, to connect the C wire to the chassis. Though it appears there's already a wire that's attached to ground, and comes right over near the thermostat wiring. I'd just put my C wire in with the other two wires, in that twist-on wire connector near the bottom of the photo.
The thermostat you posted has no common terminal (C). The blue wire that should be wired to common at the thermostat is cut off and wrapped around the harness.
You show red, white, yellow, and green wired to R,W,Y,G terminals on the thermostat, but there is no common terminal on that thermostat and the blue wire that should be wired to common is unused at the thermostat yet wired to common at the air handler.
Is there 24 volts at the air handler low voltage terminals (R and C)? You should, if not check for the door panel switch being closed. It must be closed or tape the switch closed if trying to work with the door open.
The circuit board in the air handler's circuit board should have an automotive type 3 amp fuse: it may be bad. If not and the breakers are on and proper voltage is to the furnace, then the transformer is bad.
If you switch the fan on does the fan work? If so this proves you have both high voltage and 24 volt low voltage control power available. The thermostat you show has no provision for the common side of power and looks to be battery powered. Perhaps a Maple Chase brand thermostat?
Best Answer
You indeed should be able to connect the blue wire to the C terminals at the thermostat and furnace control board and have it all work without a hitch.