I have a White Rogers 1E78-144. My house has heating only and no AC.
The current wiring only enables the fan to run when heat is required, even if I force the fan switch to ‘on’ and set heat to ‘off’. If I set it to cool or off, the fan won’t run no matter what.
In other words, if I want the fan to run, it must come with heat, which won’t happen if it’s warm enough in the house.
Is there a way to bypass the heat and just have the fan on?
Best Answer
Your thermostat cable coming from the wall appears to have only 2 wires. Therefore the thermostat can only send one command: everything on, or everything off. (This is very common in older systems.)
In order to get separate fan control, you would need at least three wires, but at the other end of the cable, the furnace would also need to be wired for this option.
To determine whether this is possible, examine your furnace and update your question with photos of the wiring diagram (if you can find it) and how the thermostat wires are currently connected to the furnace's control board.