Air Quality Sensor -G238- Function

Sensor for air quality detects pollutants in the surrounding air (mostly gasoline and/or diesel fumes).
The Climatronic Control Module -J255- evaluates the signal from the Air Quality Sensor -G238-. The A/C system is activated depending on the strength and type of polluted air.
At an outside temperature greater than approximately 2 °C (36 °F), the recirculating air mode is switched on when there is only a slight increase in the pollutant concentration.
At an outside temperature between approximately 2 °C (36 °F) and approximately -5 °C (23 °F), the change over to recirculating air mode only occurs at a sharp increase of the pollutant concentration, during which the compressor is switched on at the same time.
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 pollutant concentration. 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.
The "automatic recirculating air mode" function 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 (36 °F). If the temperature is below -5 °C (23 °F), it is not possible to use the A/C compressor.
If the vehicle has "automatic recirculating air mode", the A/C compressor can also be switched on up to a temperature of approximately -5 °C (23 °F). This also occurs when the recirculating air mode was manually switched on.
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 outside air pollution load remains relatively high for a long period of time, the sensor starts to adapt to the altered environmental conditions through an adaptation program. This is so that a recirculating air command is generally applied for less than 12 minutes if the surrounding air pollution is even. 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 A/C 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 fresh air door is closed. For this reason, a dust and pollen filter is installed with an activated charcoal layer. A filter that is saturated with pollutants is no longer effective and needs to be replaced.
To avoid the recirculation/fresh air door from shifting too frequently, a slight increase of pollutants in the ambient air does not cause it to shift immediately (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 recirculating air 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 A/C 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 foggy windows are cleared as quickly as possible, the Climatronic Control Module -J255- does not permit recirculating air mode when "Defrost" mode is on.
The Air Quality Sensor -G238- requires approximately 30 seconds to be ready to be used once the ignition has been switched on (warm-up time). During this time there is no request from the sensor to the 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 certain chemical compositions. For this reason, do not install sensors that may have come into contact with these substances.