C 20 3/4 Ton Pickup 2WD V8-350 5.7L VIN L 4-bbl (1983)
Thermal Vacuum Valve - EVAP: Description and Operation
Canister Purge Thermal Vacuum Switch (CP-TVS)
When coolant temperatures are below the switching point, canister purge is controlled by the internal orifice within the switch. However, when coolant
temperature is above the switching point, the switch opens and permits canister purge to be controlled by manifold vacuum from the carburetor port.
