Climate Control Exhaust Gas Sensor: Description and Operation

Air Quality Sensor G238 Function

• Sensor for air quality detects pollutants in the ambient air (mostly gasoline and/or diesel fumes).

• Climatronic Control Module (J255) evaluates signal from Air Quality Sensor (G238). The A/C system is activated depending on the strength and type of heavily polluted air.

- At an outside temperature greater than approximately + 2 °C (35 °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 °F) and -5 °C (23 °F), the system only switches to recirculation mode when there is a strong increase in the level of pollutants. The A/C compressor also switches on.

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 air conditioner switches to the fresh air mode.

• "Automatic recirculating air mode" can be switched off at any time. If the function is active and a request for "Automatic air recirculation" is present the A/C compressor is also switched on when outside temperatures are smaller than +2°C (35 °F). A/C compressor operation is not possible with temperatures lower than approximately -5° C (23 °F).

• 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 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 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. If a succession of peaks in the polluted air is detected, the air conditioning system can operate over a longer period of time in recirculated 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 (e.g. 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 Climatronic Control Module). The filtering of the 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 shut-off (for example, in ECON mode), the maximum duration of the "Automatic recirculated air mode" is limited to approximately 15 seconds by the Climatronic Control Module to avoid windows from fogging up.

• So that fogged windows are cleared as quickly as possible, the Climatronic Control Module does not permit recirculated air operation during the "Defrost" operating mode.

• After the ignition is switched on, the air quality sensor requires approximately 30 seconds to be operational (warm-up time). During this time there is no requirement from the sensor to Climatronic Control Module for "automatic recirculating air mode".

• The air quality sensor 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.