Fuel Evaporation System: Operation
Fuel vapors from the sealed fuel tank are 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 Sentra and Pulsar NX models, a thermal valve prevents any purging of canister by preventing the opening of the purge valve when coolant temperature is below 140°F (60°C). When the purge valve is closed on all other models, a small amount of purge air flows into intake manifold through the constant purge orifice.
A vent switching valve (if equipped) allows carburetor float bowl to vent into canister when engine is not running.