Climate Control Exhaust Gas Sensor: Description and Operation

Air Quality Sensor (G238)

• The air quality sensor recognizes the pollutants in the surrounding air (mostly gasoline and/or diesel exhaust gases) and switches the Climatronic control module (J255) to recirculating air mode.

• The Climatronic control module detects the type and intensity of air pollution at signal from air quality sensor. Depending on the outside temperature and the intensity of air pollution the Climatronic control module then decides:

- 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 pollutants in the ambient air

- At an outside temperature between approximately +2 °C and approximately -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 approximately -8 °C, the change over still occurs only at a sharp increase of pollutant concentration and then only for approximately 15 seconds (compressor is not switched on).

- If the pollution concentration in ambient air drops, the climate control system switches over 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. If the temperature is below -8 °C, then it is not possible to use the A/C compressor.

• At setting "automatic air recirculation" on the Climatronic control module, compressor can be switched on also by switching on recirculating air manually (via recirculating air button) up to a temperature of approximately -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 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 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. Refer to=> [ Dust and Pollen Filter ] Service and Repair.

• In order to avoid frequent shifting of the fresh /recirculating air doors, 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). The filtering of the charcoal insert in the dust and pollen filter will be sufficient. Refer to=> [ Dust and Pollen Filter with Activated Charcoal Insert ] Description and Operation.

• In order to avoid frequent shifting of the fresh/recirculating air doors, 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 recirculating air mode" is limited to approximately 15 seconds by the Climatronic control module to avoid windows from fogging up. Depending on the version of the A/C control head, it is possible to identify when "Econ" is on. Either the indicator lamp inside the ECON button will be on and the indicator lamp in the AC button will be off.

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

• After the ignition is switched on, air quality sensor requires approximately 30 seconds to be operational (warm-up time). During this time there is no requirement from the sensor to the 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.