Climate Control Exhaust Gas Sensor: Description and Operation

Sensor For Air Quality -G238-, Function

- The sensor for air quality recognizes pollutants in the recirculating air (mostly gasoline and or diesel exhaust) and relies on the A/C Control Head -E87- to switch to the recirculating mode.
- The A/C Control Head -E87- receives a signal from the Sensor for air quality -G238- from which the type and amount of air pollution is determined. Depending on the outside temperature and the amount of air pollution, the A/C control head then decides:
- At an outside temperature greater than approx.: +2 °C (36 °F) the recirculating air mode is switched on when there is only a slight increase in pollutants. switched in air recirculation mode
- At outside temperature between approx. +2 °C and approx. -8 °C the change-over to the recirculating air mode is only performed when the pollutant concentration strongly increases (compressor simultaneously switched on).
- At an outside temperature of -8 °C (-18 °F) a change over occurs after a severe increase of pollutants concentration, and only for 15 seconds (the compressor is not shut off).
- If the concentration drops, the climate control system switches over 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 air recirculation" is present the compressor is also switched on when outside temperatures are lower than + 2 °C. Compressor operation is not possible with temperatures lower than approx. -8 °C.
- On vehicles with "Automatic air recirculation", up to a temperature of approx. - 8 °C the compressor can be switched on when recirculated air was manually switched on (via recirculation button).
- 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. The climate control system may also operate a longer period of time in air recirculation mode, if more load peaks occur after another.
- A specific amount of time is needed for the A/C flaps to change over. In the event that a sudden increase in pollutants is encountered (e.g. when driving through a diesel exhaust cloud) gas-forming pollutants can be taken in with the fresh air into the passenger compartment until the flaps can be closed. For this reason, a dust- and pollen filter is installed with a charcoal layer A filter that has become saturated with pollutants is no longer effective and needs to be replaced.
- In order to avoid a quick shifting from the recirculating-/fresh air flap, a slight increase in pollutants entering with recirculating air will not allow for immediate shifting (the sensor does not send a request to A/C Control Head --E87-). The filtering of the charcoal insert in the dust- and pollen filter will be sufficient.
- In order to avoid quick shifting from the recirculating air/fresh air flap, the requirement from the sensor for "Automatic air recirculation" mode is at least 25 seconds (minimum duration period), especially if the pollutant concentration has been reduced considerably so that recirculating air mode is no longer necessary.
- If the compressor is shut-off (e.g. in "Econ" mode" so that the windows do fog up, the maximum duration of the "Automatic air recirculation" mode from A/C control head -E87- is limited to approx. 15 seconds.
- In order to defrost windows as quick as possible, recirculating air mode is not possible with A/C Control Head -E87- in the defrost operating mode.
- The Sensor for air quality -G238- requires approx. 30 seconds to become operational after switching the ignition on (warm-up time). During this time there is no requirement from the sensor to A/C Control Head -E87- for "Automatic air recirculation" mode.
- The Sensor for air quality -G238- contains a highly sensitive electronic component, which can be damaged if it comes in direct contact with solvents, fuels or chemicals. Therefore, do not install sensors which have come in contact with such substances.