Description of the air pollution sensor operation (VW Tiguan 1)

The air pollution sensor detects the presence of harmful substances in the outside air (mainly exhaust gases from petrol and diesel engines). The Climatronic control unit "J255" evaluates the signal from the air pollution sensor "G233". Regulation in the air conditioning system is carried out taking into account the severity and type of pollution of the outside air. At an outside air temperature of more than +2°C, the recirculation mode is switched on even at a low concentration of harmful substances. If the outside air temperature is in the range of +2...-5°C, the recirculation mode is switched on at a significant concentration of harmful substances, while the compressor of the air conditioning system is switched on at the same time. If the outside air temperature drops below -5°C, the recirculation mode is also switched on at a significant concentration of harmful substances and only for about 15 s (the air conditioning compressor does not turn on). When the concentration of harmful substances drops, the air conditioning system switches back to supply ventilation mode.

The "automatic recirculation" function can be switched off at any time. When the "automatic recirculation" function is activated, the air conditioning compressor is switched on at its request even at an outside temperature below +2°C. However, at temperatures below -5°C, the compressor is not provided for switching on. In cars with the "automatic recirculation" function, when the recirculation mode is switched on manually, the compressor can also be switched on at temperatures below -5°C. To prevent the air conditioning system from constantly operating in recirculation mode in areas with high air pollution, the sensor has a self-adjusting function (it changes its sensitivity depending on the concentration of harmful substances).

If the concentration of harmful substances in the outside air remains at a relatively high level for a long time, the sensor, in accordance with the embedded program, adapts to the changed environmental conditions so that the request to turn on the recirculation mode is issued, as a rule, for less than 12 minutes. With an increase in gas pollution, the air conditioning system can operate in the recirculation mode for a longer time. It takes some time for the air conditioning system to switch the flaps. So that with a sharp increase in gas pollution (for example, when driving through a cloud of diesel smoke) to prevent harmful substances that penetrated through the not yet closed fresh air flap from entering the cabin, a cabin filter with a layer of activated carbon is installed. A filter saturated with harmful substances cannot cope with this task - it must be replaced. To prevent frequent switching of the recirculation/fresh air ventilation flaps, some hysteresis is provided - with a slight increase in harmful substances, recirculation is not immediately switched on (the sensor does not send a request to the Climatronic control unit -J255-). For this case, the action of the activated carbon of the cabin filter is sufficient. To prevent frequent switching of the recirculation/supply ventilation flaps, the requirement for switching on "automatic recirculation" is valid for at least 25 s, even if the concentration of harmful substances decreases so much that switching on recirculation is not necessary. With the air conditioning compressor switched off (for example, when operating in ECON or AC off modes.) the maximum duration of the "automatic recirculation" activation by the Climatronic control unit "J255" is limited to approximately 15 sec. This prevents the windows from fogging up. To ensure that the windows defog as quickly as possible, the Climatronic control unit "J255" blocks the recirculation activation in the "Defrosting" mode. The air pollution sensor "G238" enters the operating mode approximately 30 sec after the ignition is switched on (heating time). During this period of time, the sensor does not issue a request to the Climatronic control unit "J255" for "automatic recirculation". The air pollution sensor "G238" is a highly sensitive electronic unit that can be damaged by contact with solvents, fuel and some chemical compounds. Therefore, do not install sensors that have been exposed to the listed substances.