Ported Vacuum Switches: Description

This device is a temperature sensitive, three outlet, vacuum valve. It is incorporated in the distributor vacuum advance supply line of certain engines to provide advanced ignition timing under prolonged idling conditions. It is designed to eliminate engine overheating at prolonged idle by switching the vacuum source from carburetor vacuum to direct intake manifold vacuum. The resultant advanced timing causes an immediate increase in engine speed to improve fan and water pump action, thus helping to lower engine temperature.