Function of the Air Quality Sensor

Function of the Air Quality Sensor

• Air Quality Sensor (G238) is installed only on vehicles with a "Comfort" version A/C system

• Air Quality Sensor (G238) detects pollutants in the ambient air (mostly gasoline and or diesel exhaust) and orders front A/C control head Climatronic Control Module (J255) to switch the air conditioning system to recirculating air mode.

• Depending on setting in MMI (Multi Media Interface), the sunroof closes as soon as front A/C control head Climatronic Control Module (J255) switches over to air recirculation mode (automatic air recirculation via the Air Quality Sensor (G238) or manual air recirculation by operating the air recirculation button). This function is equipment-dependent, its introduction has not yet been finalized. => Operating instructions

Front A/C control head Climatronic Control Module (J255) detects the type and intensity of air pollution at signal from sensor. Depending on the outside temperature and the intensity of air pollution, front A/C control head Climatronic Control Module (J255) then decides:

- At an outside temperature greater than approx:. + 2 °C (36 F) the recirculating air mode is switched on when there is only a slight increase in pollutants in the ambient air

- At an outside temperature between approx. + 2 °C and approx. - 8 °C, the change over to recirculating air mode only occurs at a sharp increase of pollutant concentration, during which the compressor is switched on simultaneously

- At an outside temperature less than approx. - 8 °C, the change over still occurs only at a sharp increase of pollutant concentration and then only for approx. 15 s (compressor is not switched on).

- If the concentration drops, the climate control system switches over to the fresh air mode.

• The function "Automatic air recirculation" can be switched off at any time. If the function is active and a request for "Automatic air recirculation" is present the compressor is also switched on when outside temperatures are smaller than + 2 °C. Compressor operation is not possible with temperatures lower than approx. - 8 °C.

• At setting "automatic air recirculation" on front A/C control head Climatronic Control Module (J255) or in MMI (Multi Media Interface), compressor can be switched on also by switching on recirculating air manually (via "recirculating air button") up to a temperature of approx. - 8 °C.

• To ensure that the A/C does not operate constantly in the recirculating air mode in areas with a consistently higher pollution, the sensor is self-adapting (it adjusts its sensitivity to the environmental conditions).

• If outside air pollution load remains high for longer period of time, the sensor starts to adapt itself to the changing environmental condition through an adaptation program (learning program), the air recirculation request in evenly polluted ambient air is therefore generally shorter than 12 minutes. The climate control system may also operate a longer period of time in air recirculation mode, if more load peaks occur after another.

• A specific amount of time is needed for the A/C flaps to change over. In the event that a sudden increase in pollutants is encountered (e.g. when driving through a diesel exhaust cloud) gas-forming pollutants can be taken in with the fresh air into the passenger compartment until the flaps can be closed. For this reason, a dust and pollen filter is installed with a charcoal layer. A filter that is saturated with pollutants is no longer effective and needs to be replaced.

• In order to avoid frequent shifting of the recirculating air/fresh air flaps, a slight increase of pollutants in the ambient air will not allow for immediate shifting (the sensor does not send a request to front A/C control head Climatronic Control Module (J255)). The filtering of the charcoal insert in the dust and pollen filter will be sufficient.

• In order to avoid frequent shifting of the recirculated air/fresh air flaps, the requirement from the Sensor for air quality (G238)sensor for "Automatic air recirculation" mode remains for at least 25 seconds (minimum duration period), even if the pollutant concentration is so far reduced that recirculated air mode is no longer necessary.

• If the compressor is shut-off (e.g. in "Econ" mode), the maximum duration of the "Automatic recirculating air mode" is limited to approx. 15 seconds by front A/C control head Climatronic Control Module (J255) to avoid windows from fogging up.

• So that fogged windows are cleared as quickly as possible, front A/C control head Climatronic Control Module (J255) does not permit recirculating air operation during the "Defrost" operating mode.

• After the ignition is switched on, Air Quality Sensor (G238) requires approx. 30 seconds to be operational (warm-up time). During this time there is no requirement from Air Quality Sensor (G238) to front A/C control head Climatronic Control Module (J255) for "Automatic recirculating air" mode.

• The Sensor for air quality (G238) contains a highly sensitive electronic component which can be damaged if it comes in direct contact with solvents, fuels or chemicals. Therefore, do not install sensors that were in contact with such substances.