Function Of Air Quality Sensor -G238-

• Sensor for air quality detects pollutants in the ambient air (mostly gasoline and/or diesel fumes).
• The Climatronic Control Module -J255- evaluates the signal from the Air Quality Sensor -G238-. The Air Conditioning (A/C) system is activated depending on the strength and type of heavily polluted air.

At an outside temperature above approximately +2 °C (35.6 °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 approximately +2 °C (35.6 °F) and approximately -5 °C (23 °F), 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 approximately -5 °C (23 °F), the system still only changes to recirculation mode when there is a strong increase in the level of pollutants. However, it only switches on for approximately 15 seconds and the A/C compressor does not switch on. If the concentration decreases, the A/C system switches to the fresh air mode.

• "Automatic recirculating air mode" can be switched off at any time. If the function is active, the A/C compressor is switched on with a request for "automatic recirculating air mode" and also when the outside air temperature is below +2 °C (35.6 °F). If the temperature is below -5 °C (23 °F), it is not possible to use the A/C compressor.
• If the vehicles has "automatic recirculating air mode", the A/C compressor can also be manually switched on when the temperature is approximately -5 °C (23 °F).
• To ensure that the A/C system does not operate constantly in the recirculating air mode in areas with a consistently higher pollution, the sensor is self-learning (it adjusts its sensitivity to the environmental conditions).
• If the pollutant level in the ambient air remains relatively high for a lengthy period, the sensor starts to adapt to the change in ambient conditions by way of an adaptation program, with the result that a recirculated-air request is generally applied for less than 12 minutes given uniform ambient air pollution. If a succession of peaks in the polluted air is detected, the A/C system can operate over a longer period of time in recirculating air mode.
• A certain amount of time is required for repositioning of the air conditioning system doors. In the event that a sudden increase in pollutants is encountered (for example, when driving through a diesel exhaust cloud) gaseous pollutants can be taken in with the fresh air into the passenger compartment until the door 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 recirculated air/fresh air door, a slight increase of pollutants in the ambient air will not allow for immediate shifting (the sensor does not send a request to the Climatronic Control Module -J255-). The filtering of the activated charcoal insert in the dust and pollen filter will be sufficient.
• In order to avoid frequent shifting of the recirculating air/fresh air door, the requirement from the 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 recirculating air mode is no longer necessary.
• If the A/C compressor is switched off (the AC  button is off), then the Climatronic Control Module -J255- limits the "automatic recirculating air mode" to approximately 15 seconds to prevent the windows from fogging up.
• So that fogged windows are cleared as quickly as possible, the Climatronic Control Module -J255- does not permit recirculated air operation during the "Defrost" operating mode.
• The Air Quality Sensor -G238- requires approximately 30 seconds to become operational once the ignition has been switched on (warm-up time). During this time there is no requirement from the sensor to Climatronic Control Module -J255- for "automatic recirculating air mode".
• The Air Quality Sensor -G238- contains a highly sensitive electronic component which can be damaged if it comes in direct contact with solvents, fuels or chemicals. For this reason, do not install sensors that may have come into contact with these substances.