Hi all, we have an original 1990 Intertherm MGH-055ABWN-07 gas furnace. The fan switch has options FAN, OFF and ON. With the thermostat/heat off, switching it to FAN (which I'm assuming is the same thing as "auto") kicks the fan on immediately and blows cool air. Same thing when switched to ON.
I am suspecting a bad limit switch but I'm not 100% sure. Our fan/limit control board is identical to this one:
How should I go about diagnosing the limit switch before buying this part?
Thank you.