Fuel Evaporation System: Operation
Fuel vapor from the sealed fuel tank is stored in the charcoal canister when the engine is stopped or idling. As the throttle valve opens and engine speed increases, vacuum opens the purge control valve and fuel vapors are drawn from canister into the intake manifold.
On California models, a thermal vacuum valve prevents any purging of canister by preventing the opening of the purge valve when coolant temperature is below 122°F/50°C.
On Federal models, the control unit closes the canister control solenoid valve to prevent any purging of the canister by preventing the opening of the purge valve when coolant temperature is below 140°F (60°C), as relayed to the control unit from the thermal vacuum valve.
A vent switching valve allows carburetor float bowl to vent into canister when engine is not running.