Vacuum Switch: Description and Operation

Two vacuum switches and a thermoswitch are incorporated into the emission control system. When coolant temperature is below 140°F (60°C), and manifold vacuum is less than 7.9 inch Hg, (200 mm Hg) for vehicles equipped with manual transmission and 4 inch Hg, (120 mm Hg) for vehicles equipped with automatic transmissions. The ECU opens the solenoid valve circuit by receiving thermoswitch and vacuum switch signals. When manifold vacuum is less than 3.3 inch Hg, (86 mm Hg) the ECU issues a signal to the solenoid valves that the amount of air metered is constant.