Air Quality Sensor -G238- Function

Function Mode 

• The Air Quality Sensor -G238- requires approximately 30 seconds to reach its operating temperature after the ignition is switched on. During the warm-up phase, the function of the Air Quality Sensor -G238- is limited.
• The Air Quality Sensor -G238- detects pollutants in the surrounding air (usually gasoline and/or diesel exhaust) and prompts the Climatronic Control Module -J255- to switch the A/C system to recirculating air mode.
• The Climatronic Control Module -J255- and the control head recognize the type and intensity of the air pollutant from the signal from the Air Quality Sensor -G238-. Based on this information, the Climatronic Control Module -J255- then determines if and when the A/C system switches to recirculating air mode.

Example: 

-- At an exterior temperature above approximately +2 °C (35.6 °F), the recirculation mode is switched on upon request from the Air Quality Sensor -G238- when there is only a slight increase in the pollutant concentration.

-- At an outside temperature between approximately +2 °C (35.6 °F) and approximately -8 °C (17.6 °F), the change over to recirculating air mode only occurs at a sharp increase of pollutant concentration, during which the compressor is switched on simultaneously.

-- When the exterior temperature is less than approximately -8 °C (17.6 °F) and the A/C compressor is switched off, the change over only occurs when there is an increase in the pollutant concentration and only then for approximately 15 seconds.

• The indicator lamp in the AC  or A/C  button does not light up.
• The maximum duration of the "Automatic recirculating air mode" is limited to approximately 15 seconds by the Climatronic Control Module -J255- so that the windows in the vehicle interior do not fog up.

-- 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 (35.6 °F). If the temperature is below -8 °C (17.6 °F), then it is not possible to use the A/C compressor.
• At the "automatic recirculating air mode" setting on the Climatronic Control Module -J255- A/C control head, the A/C compressor can also be switched on by switching on the recirculating air mode manually (via the recirculation button  ) up to a temperature of approximately -8 °C (17.6 °F).
• To ensure that the A/C system is not constantly working in recirculating air mode in areas with consistently high air pollution, the Air Quality Sensor -G238- is self-adapting (it adjusts its sensitivity to the environmental conditions).
• If the outside air pollution load remains relatively high for a long period of time, the Air Quality Sensor -G238- starts to adapt itself to the altered environmental conditions through an adaptation program so that the air recirculation request is generally shorter than 12 minutes in uniformly polluted surrounding air. 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 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.
• To prevent excessive operation of the fresh air/air recirculation doors, the door is not actuated immediately if there is a nominal increase in pollutants in the surrounding air (the Air Quality Sensor -G238- 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 operation of the fresh air/air recirculation doors, the request from the Air Quality Sensor -G238- 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.
• The Climatronic Control Module -J255- does not allow any air circulation in "defrost" mode so that the window glass can defog as quickly as possible.
• The Air Quality Sensor -G238- requires approximately 30 seconds to become operational once the ignition has been switched on (warm-up time). There is no request sent to the Climatronic Control Module -J255- control head for "Automatic recirculating air mode" at this time.
• 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 chemicals. For this reason, do not install sensors that may have come into contact with these substances.