C 10 1/2 Ton Pickup 2WD L6-250 4.1L VIN D 2-bbl (1982)
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Thermal Vacuum Valve: Service and Repair
EFE Thermal Vacuum Switch (EFE-TVS)
Early Fuel Evaporation Thermal Vacuum Switch (EFE-TVS)
When engine coolant temperature is below the calibration point of the switch, manifold vacuum flows through ports 2 and 3 of this switch to the
EFE actuator, closing the EFE actuator. Above the switching point, port 3 of this switch is blocked and the EFE vacuum actuator is vented to
atmosphere through port 1.