Hi. I have a 1988 Snyder General furnace Model GDA060A012AIN with a White-Rogers Digital Comfort-Set II thermostat. My furnace blower is constantly running, even with the thermostat on/auto fan setting set to auto and the thermostat heat/cool/off option turned to off, it still runs even with the thermostat removed from its wall socket. The only way the blower is off is when power to the furnace is off or the blower door is open (the cover is removed).
My thought is that either the thermostat is sending a signal to the blower to run even when the blower is set to the off position (a bad thermostat), or the blower relay switch is bad and runs the blower even when no signal is present (bad blower relay). But based on the problem still happening when I remove the thermostat unit from the wall base I'm guessing that it is the blower relay.
What is the easiest way for me to figure out what is actually wrong? Besides calling a service technician.