Air Quality Sensor Function
Air Quality Sensor Function
=> [ Air Quality Sensor, Checking ]
• The air quality sensor detects pollutants in the ambient air (mostly gasoline exhaust) and instructs the Climatronic control module (J255) A/C control head to switch the A/C system to " recirculation mode".
• A/C control head Climatronic Control Module (J255 ) detects the type and intensity of air pollution at signal from Air Quality Sensor (G238). Depending on the outside temperature and the intensity of air pollution, A/C control head Climatronic Control Module (J255) 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 in the ambient air
- At an outside temperature between approximately + 2°C and approximately - 8°C, the switch to recirculation 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 s (compressor is not switched on).
- If the concentration drops, the A/C 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 smaller than + 2 °C. Compressor operation is not possible with temperatures lower than approximately - 8 °C.
• In vehicles with "automatic air recirculation", the compressor can be switched on at up to a temperature of approximately - 8? when recirculated air was switched on manually (via the "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 Air Quality Sensor (G238) is self learning (it adjusts its sensitivity to the environmental conditions).
• If outside air pollution load remains high for longer period of time, the Air Quality Sensor (G238) 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 (e.g. when driving through a diesel exhaust cloud) gaseous pollutants can be taken in with the fresh air into the passenger compartment until the doors 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 ] A/C System Control and Regulation Components.
• In order to avoid excessive switching of the "recirculation/fresh air flaps", a slight increase of pollutants in the ambient air does not cause immediate switching (the air quality sensor ( G238) does not send a request to the Climatronic control module (J255) A/C control head). The filtering of the charcoal insert in the dust and pollen filter will be sufficient. Refer to => [ Dust and Pollen Filter with Activated Charcoal Filter Unit ] A/C System Control and Regulation Components.
• In order to avoid excessive switching of the "recirculation/fresh air flaps", the request from the air quality sensor (G238) for "automatic recirculation mode" remains for at least 25 seconds (minimum duration period), even if the pollutant concentration is so far reduced that the recirculation mode is no longer necessary.
• If the compressor is switched off (e.g. in "Econ" mode), the maximum duration of the "automatic recirculation mode" is limited to approximately 15 seconds by the Climatronic control module (J255) A/C control head to prevent the windows from fogging up.
• So that fogged windows are cleared as quickly as possible, the Climatronic control module (J255) A/C control head does not permit the recirculation mode during the "defrost" operating mode.
• After the ignition is switched on, Air Quality Sensor (G238) requires approximately 30 seconds to be operational (warm-up time). During this time there is no requirement from Air Quality Sensor (G238) to front A/C control head Climatronic Control Module (J255) for "Automatic recirculating air" 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. For this reason, do not install any air quality sensors (G238) that may have come into contact with these substances.
Air Quality Sensor, Checking
• Vehicle Diagnosis, Testing and Information System ( VAS 5051A) e.g. with the diagnostic cable (VAS 5051/5A) and the K-wire adapter (VAS 6017B) (or the K-wire adapter (VAS 6017A)
• Test gas "D 007 855 A2"
• Vehicle standing in a clean atmosphere (away from running engines, exhaust vents, etc.)
• Engine compartment and the plenum chamber are clean (not contaminated with oil or fuel)
• The engine compartment and the plenum chamber were not sprayed with cleaning agents or preservatives containing solvents
Checking
- Remove the plenum chamber cover.
- With the ignition switched off, connect the Vehicle Diagnosis, Testing and Information System (VAS 5051A) e.g. with the diagnostic cable (VAS 5051/5A) and the K-wire adapter (VAS 6017B) (or the K-wire adapter (VAS 6017A)) to the 16-pin data link connector (DLC). Refer to => [ VAS 5051A, Connecting and Selecting Functions ] VAS 5051A, Connecting and Selecting Functions.
- Start engine.
- Check DTC memory. Refer to => [ DTC Memory, Interrogating ] DTC Memory, Interrogating.
- Set operating mode "Auto" on A/C control head Climatronic Control Module (J255).
- The button for "automatic recirculation" - A - is pressed (the LED lamp in button - A - illuminates).
- Wait 30 seconds (warm up time for Air Quality Sensor (G238)).
Indication on the display of the Vehicle Diagnosis, Testing and Information System (VAS 5051A).
- Select function "08 - Read Measuring Value Block".
Indication on display of Vehicle Diagnosis, Testing and Information System (VAS 5051A):
• Display field - 1 - indicates request to input display group.
• Display field - 2 - shows input keyboard.
- Enter the desired display group number "014" in display field - 2 - via the keyboard. Refer to => [ Display Group Overview ] Display Group Overview.
- Press the Q button to confirm the entry.
- Read indications shown in display fields "3" and " 4".
• Display field "4" shows the operating condition of the A/C system (fresh air or recirculation mode) and display field "3" shows the signal condition of the air quality sensor (G238). Explanation of possible displays. Refer to => [ Display Group 014 ] Measured Value Blocks for Display Groups 011 Through 019 and => [ Display Group 014 ] Measured Value Blocks for Display Groups 011 Through 019.
Target value in display field "4"
• "00" (no request for "recirculation mode" present, A/C system in the fresh air mode)
Or
• "60" ("partial recirculation mode", fresh air and back pressure flap open)
- Place spray head - A - of the test gas bottle over the air inlet of air quality sensor (G238) - B - (in version "1" of the air quality sensor (G238)).
- Place spray head - A - of the test gas bottle over the air inlet of air quality sensor (G238) - B - (in version "2" of the air quality sensor (G238)).
- Press spray button - C - of the test gas bottle for 1 second.
• The air quality sensor (G238) is available in different housings. Version "1" is installed at production start. This sensor will be replaced gradually by version "2" but the mode of operation is identical.
• The test gas canister is filled with pure oxygen with a specific nitrogen oxide component.
• If cigarette smoke or cigarette lighter gas (gas is heavier than air, therefore remove the air quality sensor (G238) and turn it around) acts on the air quality sensor (G238), it also reacts.
- Read indication in display field "4".
Specification:
• "10" (request for "automatic recirculation mode " present, request is fulfilled, A/C system switches to recirculation mode)
- Wait a short period time (approximately 1 minute, depending on amount of test gas sprayed on Air Quality Sensor (G238)).
- Read indication in display field "4".
Specification:
• "00" (no request for "recirculation mode" present, A/C system in the fresh air mode)
Or
• "60" (partial recirculation mode)
• In order to avoid excessive switching of the recirculation/fresh air flaps, the request of the air quality sensor (G238) for "automatic recirculation mode" remains for at least 25 seconds (minimum duration period), even if the pollutant concentration is so far reduced that recirculated air mode is no longer necessary.
- Operate switch for wiper/washer system until Windshield Washer Pump (V5) has delivered fluid for approximately 2 seconds.
- Read indication in display field "4".
Specification:
• "30" (request for "recirculation mode" due to windshield wiper system, the A/C system switches for approximately 10 seconds to the recirculation mode)
• The request for "recirculation mode" when operating the windshield wiper system is not implemented in all versions of the Climatronic control module (J255) A/C control head
- Wait briefly.
- Read indication in display field "4".
Specification:
• "00" (no request for "recirculation mode" present, A/C system in the fresh air mode)
Or
• "60" (partial recirculation mode)
• Depending on the composition of the windshield washer fluid, the Air Quality Sensor (G238) can determine impurities in the air and request for "Automatic air recirculation".
• If no switch to recirculation mode occurs when operating the switch for the windshield wiper system, check the function of the relay for wiper/washer intermittent relay (J31) (the information " wash windshield" is received by the steering column electronic systems control module (J527) via the comfort data bus system) (read the measuring value block, display group "019"). Refer to => [ Display Group 018 ] Measured Value Blocks for Display Groups 011 Through 019
If the function of Air Quality Sensor (G238) is OK for this test and there is a customer complaint continue as follows:
- Check dust and pollen filter for dirt.
- Connect the Vehicle Diagnosis, Testing and Information System (VAS 5051A) for example and select the function " 08 read the measured value block" for the A/C system.
- Enter display group number "014" and read the displays in display fields "3" and "4".
• Second person is required to read out values displayed whilst driving.
• Pay attention to safety precautions.
- Conduct a test drive. First drive the vehicle in an area with relatively clean air (the system functions in fresh air mode) and then drive in an area with pollution (e.g. on an uphill road with truck traffic)
• The display in display fields "3" and "4" of display group "014" must change e.g. when driving through a Diesel exhaust cloud. Refer to => [ Display Group Overview ] Display Group Overview.
• Also note information regarding the dust and pollen filter. Refer to => [ Dust and Pollen Filter with Activated Charcoal Filter Unit ] A/C System Control and Regulation Components and functions of the air quality sensor (G238). Refer to => [ Air Quality Sensor Function ] Air Quality Sensor Function.