Lennox - Fan Won't Stop Running
Blower fan stuck on. Blow fan won't turn off.
There is two controls in the furnace that could keep the fan on. The fan relay and the fan switch that it part of the fan and limit control. The fan relay is energized when you turn the fan switch on at the thermostat. When the fan relay is energized the blower will run the "cooling speed" which is usually a higher speed than the heating speed. The fan switch, that is part of the fan and limit control, turns the blower on when the heat exchanger hot.