See Figure 1
This system consists of an expansion chamber, an activated charcoal filter, and a hose which connects the parts into a closed system.
When fuel in the gas tank expands due to heat, the fuel travels to the expansion chamber. Any fumes generated either in the gas tank or the expansion chamber are trapped in the activated charcoal filter found in a line connecting the tank and chamber. The fumes are purged from the filter when the engine is started. Air from the engine cooling fan is forced through the filter when the engine is started. From the filter, this air/fuel vapor mixture is routed to the inside of the air cleaner where it is sent to the engine to be burned.
1976 and later Type 2 models have an Evaporative Emission Control (EEC) cutoff valve which prevents fuel fumes from entering the air cleaner when the engine is stopped or idling. The cutoff is located in the air cleaner body. To test the valve, turn off the engine and disconnect the charcoal filter to air cleaner hose from the charcoal filter (this hose is usually transparent). Blow into the hose. The valve should be closed and no air should be going into the air cleaner. If the cutoff valve is open and air is getting through, the valve must be replaced.
The only maintenance required on the system is checking the tightness of all hose connections, and replacement of the charcoal filter element at 48,000 miles or 2 year intervals (whichever occurs first).
The filter canister is located under the right rear fender on Beetles and Super Beetles, at the lower right-hand side of the engine compartment on Karmann Ghias, at the upper right-hand side of the engine compartment on Type 3 models, beneath the floor near the forward end of the transaxle on Type 4 models and in the engine compartment on Type 2 models.