Operation CHARM: Car repair manuals for everyone.

Cabin Air Filter / Purifier: Description and Operation






Dust and Pollen Filter with an Activated Charcoal Filter Element

The activated charcoal filter continues to function as a dust and pollen filter. However, the activated charcoal filter can also filter out gaseous pollutants, for example, ozone, benzene, nitrogen dioxide, etc. from the air flow. The basic task of the activated charcoal layer in the dust and pollen filter is to keep load peaks out of the passenger compartment.

The activated charcoal also has the task of removing certain gaseous contaminants from the air flowing through. The activated charcoal layer in the dust and pollen filter reacts differently to various pollutants in the air.

Certain pollutants bond permanently in the active-carbon layer.

Others are converted into noxious bonds like in a catalytic converter.

For the rest the activated charcoal works as a condenser (capacitor). With increasing load pollutants are absorbed, until a certain saturation is reached. If the amount of pollutants decreases, the activated charcoal layer continuously releases the absorbed particles.

Under the following operating conditions the dust and pollen filter must be replaced earlier than required, because a certain amount of pollutant particles is permanently bonded to the activated charcoal layer.

If the vehicle is driven in areas with heavy air pollution.

When operating a vehicle without an Air quality sensor (G238) (Basic version) and thus without automatic recirculation mode.

When operating a vehicle with an Air quality sensor (Comfort A/C system) with automatic recirculation mode switched off.

In vehicles with an Air quality sensor (Comfort A/C system), the A/C system should be operated as continuously as possible in the automatic recirculation mode.

The active carbon layer in the dust and pollen filter is saturated after a certain time.

A saturated filter can no longer absorb pollutants and the pollutants can flow through freely.