Air Quality Sensor -G238- FUNCTION

NOTE:

The Air Quality Sensor -G238- -3- is only installed on a "Convenience" A/C system version (on an automatic climate control system). It is integrated together with the Humidity Sensor In Fresh Air Intake Duct -G657- -1- in the housing -2-.

Courtesy of AUDI OF AMERICA, LLC

There are different versions of the Air Quality Sensor -G238- -3- and the Humidity Sensor In Fresh Air Intake Duct -G657- -1-. Pay attention to the correct allocation.

• The Air Quality Sensor -G238- (and the Humidity Sensor In Fresh Air Intake Duct -G657-) uses a sensor to determine the NOx level (nitrogen oxide) and CO level (carbon monoxide) in the air flowing by and exchanges this information with the Climatronic Control Module -J255-.
• The measured values for the Air Quality Sensor -G238- (and the Humidity Sensor In Fresh Air Intake Duct -G657-) are evaluated by the Climatronic Control Module -J255-. Upon request, the Climatronic Control Module -J255- switches to recirculating air mode if no shut-off condition is present. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding  " function.

• The Air Quality Sensor -G238- requires a short period of time 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- identifies the type and intensity of the air pollutant by the signal from the Air Quality Sensor -G238-. The Climatronic Control Module -J255- also receives information about whether the "automatic recirculating air mode" function is switched on or off from the Multimedia System Control Head -E380- via the Data Bus. Based on this information, the Climatronic Control Module -J255- then determines if and when the A/C system switches to recirculating air mode. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding  " function.

Example: 

-- At an outside temperature above approximately 2 °C (36 °F), the recirculating air 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 exterior temperature below approximately -1 °C (30 °F) and with the A/C compressor switched off, the switch-over will only take place if there is a sharp increase in the pollutant concentration. If there is another increase in the pollutant concentration for approximately 15 seconds within approximately two minutes, the Climatronic Control Module -J255- will not switch to "automatic recirculating air mode" during this time.

• If the indicator lamp in the A/C  button (installed in the Front A/C Display Control Head 4 -E777-) does not come on, the Climatronic Control Module -J255- limits the maximum duration of the "automatic recirculating air mode" to approximately 15 seconds so that the vehicle windows do not fog up in the vehicle interior.

-- If the pollution concentration in the fresh air that is drawn in drops, the A/C system switches back over to fresh air mode.

• The duration of the "automatic recirculating air mode" depends on the Climatronic Control Module -J255- version, the setting on the Multimedia System Control Head -E380-, the Front A/C Display Control Head 4 -E777- and the Humidity Sensor -G355- measured values.

-- If the exterior temperature is lower than approximately 10 °C (50 °F) and the "automatic recirculating air mode" function is activated on the Multimedia System Control Head -E380-, the system stays, for example, approximately 30 seconds in "automatic recirculating air mode". After this, it switches to fresh air mode. If another increase in the pollutant concentration occurs within approximately two minutes, the Climatronic Control Module -J255- does not switch over to "automatic recirculating air mode" during this time.

• 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 exterior temperature is below 2 °C (36 °F). If the temperature is below -5 °C (23 °F), then it is no longer possible to use the A/C compressor.
• If the "automatic recirculating air mode" is set in the MMI (Multi Media Interface), the A/C compressor can be switched on up to a temperature of approximately -5 °C (23 °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 vehicle interior until the back pressure- /fresh air doors can be closed (and the air recirculation doors are opened). For this reason, a dust and pollen filter is installed with an activated charcoal layer. A filter that is saturated with pollutants is no longer effective and needs to be replaced.
• To prevent excessive operation of the back pressure/fresh air door and the air recirculation door, the door is not immediately activated 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 excessive operation of the back pressure/fresh air door and the air recirculation door, a request from the Air Quality Sensor -G238- for "automatic recirculating air mode" remains active for at least 25 seconds (minimum duration period), even if the pollutant concentration in the air has reduced so much that recirculating air mode is no longer necessary.
• The Climatronic Control Module -J255- does not allow recirculating air mode in "defrost" mode (recognizable by the illumination of the indicator lamp in the Defrost Button -E782-) so that the fogged up windshield, rear window and door windows can defog as quickly as possible (a request from the Air Quality Sensor -G238- is not implemented).
• The Air Quality Sensor -G238- requires a short period of time to become operational once the ignition has been switched on (warm-up time). During this time, no request is sent to the Climatronic Control Module -J255- control head for the "automatic recirculating air mode".