Cabin Air Filter / Purifier: Description and Operation

Dust and Pollen Filter with Activated Charcoal Filter Unit

• The dust and pollen filter with the additional filter insert with activated charcoal is installed in vehicles equipped with the "Comfort" version of the Climatronic Control Module (J255) A/C control head. These vehicles are also equipped with an Air Quality Sensor (G238) => [ Air Quality Sensor Function ] Description and Operation.

• 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 task of the active charcoal filter element is to store (catch) the gaseous pollutants of the incoming air until the back pressure / fresh air doors are closed and the climate control system operates in recirculating mode. The change over from fresh to recirculating mode occurs via the "Comfort" version of the Climatronic Control Module (J255) A/C control head, as soon as the Air Quality Sensor (G238) detects gaseous pollutants in the ambient air (the "automatic air recirculation mode" must be selected).

• In model year 2008, 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.

• 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 load increasing, pollutants are absorbed for as long until a certain saturation point 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 switched off.

• If possible, vehicles with A/C system with one Air Quality Sensor (G238) should always be operated in "automatic air recirculation" mode. If it is necessary or desired to switch the function off, the following should 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 (G238) is keep the load peaks out from the passenger compartment. When doing this, note the following:

- If a vehicle is driven in an area with relative clean ambient air (with little gaseous pollutants in the air), the change over from fresh into recirculating mode occurs at different point in time as in an area with high basic load (e.g. industrial area).

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