Vacuum Override Motor Test

With duct assembly installed on car, engine cold and engine compartment temperature less than 100°F, valve plate should be in approximately half open position. If not, check for possible interference of plate, duct and vacuum motor which would cause binding. Start engine and observe valve plate position while engine is cold. Plate should be in full heat on position. If valve remains in half open position, remove vacuum hose at override vacuum motor and check for vacuum. If vacuum is less than 15" Hg, check for vacuum leaks. If vacuum is sufficient, and no binding exists, remove vacuum motor and connect to another vacuum source. If motor rod moves a minimum of 1/2" motor is functioning correctly and should be reinstalled and a check made for interference and misalignment along with a check of thermostatic bulb. If motor rod does not move a minimum of 1/2", motor is defective and should be replaced.