"After vaccum my furnace(Heat only, Day and Night furnace with model #396GAW00100-ACAA), the fan stop blow but burner will be on when I adjust the temperature below the setpoint on thermostat. My fan had problem last year. It will not stop even after burner off for long time. I had to tap side of the furnace to stop it. It happens 3 or 4 times last year. Is ther a relay to control the fan and where it is? how it look like? I have electrical background to fix but need help. Please."