Cabin Air Filter / Purifier: Description and Operation

Dust and Pollen Filter with Activated Charcoal Insert

• There are different versions of the dust and pollen filter without and with filter insert with activated charcoal.Refer to Electronic Parts Catalog (ETKA). On vehicles equipped with the "Comfort" A/C system, there is currently a dust and pollen filter with an activated charcoal filter element installed; on vehicles equipped with the "Basis" A/C system, there is a dust and pollen filter without the activated charcoal filter element installed.

• In model year 2012, vehicles with a "Comfort" A/C system will have a modified dust and pollen filter with an activated charcoal filter element installed as a running change. This filter with an improved interception rate for fine particulates has approximately the same air resistance values as the filter installed prior to the change, and for this reason will be in installed in vehicles built up to the change. Refer to Electronic Parts Catalog (ETKA).

• The dust and pollen filter has an additional filter insert made of activated charcoal on vehicles with the "Comfort" A/C system. These vehicles also have an air quality sensor (G238). Refer to => [ Air Quality Sensor (G238) and Humidity Sensor in Fresh Air Intake Duct (G657) Function ] Description and Operation.

• The activated charcoal filter element functions as a dust and pollen filter, however in addition the activated charcoal filter can also filter out gaseous pollutants, for example, ozone, benzene, nitrogen dioxide 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 activated charcoal layer.

- Others are converted into innoxious bonds as 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.

• Because a portion of the gaseous pollutant particles as well as dust and pollen bond permanently to the activated charcoal layer, the dust and pollen filter should be changed more often than scheduled under the following conditions:

- If vehicle is driven in areas with constant strong air pollution. the activated charcoal layer in the dust and pollen filter is saturated faster than planned.

- If vehicle is predominantly driven with the "automatic recirculating" mode switched off.

• If possible, vehicles with A/C system with one air quality sensor should always be operated in "automatic air recirculation" mode. However, if it is desired or necessary to switch this mode off, the following must be observed:

- 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 allows them to pass unhindered.

• The most important task of the dust and pollen filter activated charcoal filter element and the air quality sensor is to keep the load peaks out of the passenger compartment. For this the following must be observed:

- The vehicle is driven in an area with relatively clean air. with few air pollutants. The switch-over from fresh air mode to recirculating air mode will occur at a different time than on a vehicle driven in an area that has high air pollutants, for example, in an industrial area.

- Independently of the basic load, the change-over from fresh to recirculating mode always occurs, when the pollutant-load increases (for example when driving to through an exhaust cloud of a diesel truck).