C 20 3/4 Ton Pickup 2WD V8-305 5.0L VIN H 4-bbl (1982)
Thermal Vacuum Valve: Description and Operation
Fig. 30 - Thermal Vacuum Switch
Used on some engines, the thermal vacuum switch prevents vacuum from actuating the air control and air switching valves until the engine reaches
a predetermined temperature (120° F). When engine temperature reaches this calibration point, the thermal vacuum switch opens and allows
vacuum to pass through it to the air control and air switching valves.