Cabin Air Filter / Purifier: Description and Operation

Dust and Pollen Filter with Activated Charcoal Filter Unit

• Vehicles wit the Basis and Comfort A/C systems have a dust and pollen filter with an activated charcoal air filter. Vehicles with the Comfort A/C system also have an Air Quality Sensor (G238).

• 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.

• On vehicles with a Comfort version A/C system, the task of the activated charcoal is to absorb gaseous contaminants in the air flow for as long until the A/C system switches over to air recirculation mode (fresh air/recirculating air door seals the fresh air intake channel and opens the air recirculation intake channel). The change over from fresh to recirculating mode occurs via the Climatronic Control Module (J255) , as soon as air quality sensor detects gaseous pollutants in the ambient air (the automatic air recirculation mode must be selected).

• On vehicles with Basic version A/C system, the task of the activated charcoal is primarily to absorb gaseous contaminants from the incoming airflow when contaminant levels increase (and then possibly to emit the contaminants again slowly). If filter is saturated, it permits gaseous contaminants to stream in freely.

• 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 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 vehicles is driven in areas with strong air pollution.

- If vehicle is predominantly driven with the automatic air recirculation mode switched off.

• On vehicles with Comfort version A/C system (with air quality sensor ) the A/C system should be operated as continuously as possible in the automatic air recirculation function. 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 cannot absorb any more contaminants and permits them to flow in freely (as on the Basic version A/C system).

• On vehicles with Comfort version A/C system, the essential task of the activated charcoal in the dust and pollen filter (and of air quality sensor ) is to keep the load peaks out of the passenger compartment. For this the following must be observed:

- 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 (for example, 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).