Cabin Air Filter / Purifier: Description and Operation

Dust and Pollen Filter with Activated Charcoal Insert

• Dust and pollen filter with additional filter element with activated charcoal is installed at this time in vehicles with or without A/C system (only with heater). In vehicles with automatically regulated A/C system, an Air Quality Sensor (G238) (=> [ Air Quality Sensor (G238) ] Description and Operation) may also be installed (currently as optional equipment).

• 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 for example, ozone, benzene, nitrogen dioxide from the air flow.

• The task of the active carbon filter element is to store (catch) the gaseous pollutants of the incoming air, until the back pressure door (fresh air door) is closed and the climate control system operates in recirculating mode. The change over from fresh to recirculating mode occurs via the Climatronic Control Module (J255) , as soon as air quality sensor (G238) detects gaseous pollutants in the ambient air (the "automatic air recirculation" 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 air mode" 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 the pollutants can flow through freely.

• 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).

- 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).