I have looked through the archives and do not see this answered,
My furnace unit is in the attic, When I looked on the control board, all the wires seem to be correct except the Y.
These are the wires that are right.
However, the yellow cable goes to a wire nut, and is connected to a wire that goes down to my outside fan, and then comes back on another red wire that goes to C.
I attached a photo showing the wires (ignore the Y wire label on the top red wire, I did that to help me distinguish it from the other red wire.)
I tried attached the upper red wire to the Y on the C-wire adapter, and everything seemed to work, but the AC never worked. It just blew room temperature air.
I put the old thermostat back on until I can get this figured out.
I don’t know what the red/white wire that comes from the outdoor fan unit is for. Any HVAC people on here that can assist?
This is a Trane furnace. Gas heat, electric air.