Impala V8-305 5.0L VIN H 4-bbl (1982)
Thermal Vacuum Valve - EVAP: Description and Operation
Thermal Vacuum Switch
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When coolant temperature is below the switching point canister purge is controlled by the internal orifice within the switch.
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When coolant temperature is above the switching point the switch opens and canister purge is controlled by manifold vacuum--from the
carburetor port.