Thermal & Vacuum Switches

The feedback system does not respond quickly enough to provide good driveability under full-load or cold operation. The thermal and vacuum switches are used to limit closed loop operation under these conditions. When engine coolant is below 140°F (60°C) and manifold vacuum is less than 8 in. Hg (2-bbl.) or 12 in. Hg (1-bbl.), the thermal switch and one of the vacuum switches signal the electronic control unit to shut the solenoid(s) off. Closed loop operation is also prevented by the second vacuum switch when the engine is warm and vacuum falls below 4 in. Hg.