Evaporative Emissions System: Description and Operation

Fig. 19 Evaporative emission control system.:

Fig. 20 Evaporative emission control system.:

3A-C, 3E, 4A-C & 4A-LC ENGINES

On this system, Figs. 19 and 20, when ignition switch is off, the outer vent control valve is open and fuel vapors from the float chamber and fuel tank are absorbed by the charcoal canister.
When the ignition switch is turned on, the outer vent control valve closes. When coolant temperature is below 109°F or above 131°F and engine speed is below 1180 RPM, the vacuum switching valve is off and fuel vapors from the tank are absorbed by the charcoal canister.
When coolant temperature is above 131°F and engine speed is above 1600 RPM, the vacuum switching valve is on and vapors are led from the canister to the intake manifold.