Cabin Air Filter / Purifier: Description and Operation

Dust and Pollen Filter with Activated Charcoal Insert

• A dust and pollen filter with additional activated charcoal filter insert is installed together with the Air Quality Sensor ( G238).

• The activated charcoal filter element continues to function as a dust and pollen filter, however in addition the activated charcoal filter can also filter out gaseous pollutants e.g. ozone, benzene, nitrogen dioxide from the air flow.

• The role of the activated charcoal is to store the impurities in the through-flowing air until the fresh air door is closed and the air conditioning system is operating in air recirculation mode. The change over from fresh to recirculating mode occurs via the Climatronic Control Module (J255), as soon as the air quality sensor detects gaseous pollutants in the ambient air the "automatic recirculating" mode must be selected.

• 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 vehicle is driven in areas with strong air pollution.

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

On vehicles without an air quality sensor and without "automatic recirculation" mode.

• If possible, vehicles with climate control using the air quality sensor should always be operated in "automatic recirculating" 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 and air quality sensor is keep the load peaks out from the passenger compartment. For this the following must be observed:

If a vehicle is driven in an area with relatively clean air with little air pollution, the system will switch from fresh air mode to recirculation mode occurs at a different point in time than when in an area with heavy air pollution such as an industrial area.

The switch from fresh to recirculating mode always occurs when the level of pollutants increases, regardless of what the level originally was like when driving through an exhaust cloud.

• The filter with activated charcoal can be installed in all vehicle types also vehicles without air quality sensor. The same limitations apply to these vehicles as on climate control systems with the "automatic recirculation" mode switched off.