Climate Control Exhaust Gas Sensor: Description and Operation

Air Quality Sensor (G238)

• The Air Quality Sensor detects pollutants in the ambient air (mostly gasoline and/or diesel fumes).

• Climatronic Control Module (J255) evaluates signal from the Air Quality Sensor. 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 (35.6 °F), recirculation 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 switch to recirculation mode only occurs at a sharp increase in the pollutant level. The A/C compressor is switched on at the same time.

At an outside temperature of less than approximately -5° C (23 °F), the system still only changes to recirculation mode when there is a significant 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.

• The function Automatic air recirculation can be switched off at any time. If the function is active and a request for automatic recirculation mode is present, the A/C compressor is also switched on at outside temperatures of less than + 2° C (35.6 °F). If the temperature is less than approximately - 5° C (23 °F), it is not possible to use the A/C compressor.

• In the case of vehicles with automatic recirculation mode, the A/C compressor can be switched on at a temperature of up to approximately - 5° C (23 °F) even if recirculation mode is activated manually.

• 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 (for instance 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 switching of the recirculated/fresh air door, the request from the sensor for automatic recirculation mode is present for at least 25 seconds (minimum duration period), even if the pollutant level in the air is so far reduced that recirculation mode is no longer necessary.

• If the A/C compressor is turned off (for example, the AC button is off), the Climatronic control module limits the maximum duration of 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 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 recirculated 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.