Thermal Vacuum Spark Control Valve

This valve is used on California 4-cylinder engines and is located in air cleaner. It passes manifold vacuum to port "1" of CTO valve and distributor vacuum advance mechanism only when air cleaner intake is below 63°F (17°C). At temperatures above 63°F (17°C), manifold vacuum is prevented from reaching CTO valve until coolant temperature reaches spark CTO valve switching point. See Figure.