The air pollution sensor recognizes the presence of harmful substances in the outdoor air (mainly exhaust gases from petrol and diesel engines). The Climatronic control unit -J255- evaluates the signal from the air pollution sender -G233-. The air conditioning system is controlled according to the severity and type of outdoor air pollution. At an outside air temperature of more than +2°C, the recirculation mode is switched on already 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 air conditioner compressor is switched on at the same time. If the outside air temperature drops below -5°C, the recirculation mode is also switched on with a significant concentration of harmful substances and only for about 15 seconds (air conditioner compressor does not turn on). When the concentration of harmful substances drops, the air conditioner switches back to fresh air mode.
Function "automatic recycling" can be turned off at any time. When the function is activated "automatic recycling" the compressor of the air conditioning unit is switched on at its request even when the outside temperature is below +2°C. However, at temperatures below -5°C, the compressor will not turn on. On vehicles with automatic recirculation function" when turning on the recirculation mode manually, the compressor can also turn on up to a temperature of -5°C. So that in places with strong gas pollution the air conditioner does not constantly work in recirculation mode, the sensor has a self-tuning function (it changes its sensitivity depending on the concentration of harmful substances).
If the concentration of harmful substances in the outdoor air remains at a relatively high level for a long time, then the sensor, in accordance with the programmed program, adapts to the changed environmental conditions so that the request to turn on the recirculation mode is issued, as a rule, in less than 12 minutes. With an increase in gas contamination, the air conditioner can work in recirculation mode for a longer time. The air conditioner takes some time to switch the dampers. So that with a sharp increase in gas content (e.g. when driving through a cloud of diesel smoke) harmful substances that have penetrated through the fresh air damper that has not yet been closed have not entered the passenger compartment; installation of a cabin filter with a layer of activated carbon is provided. A filter saturated with harmful substances does not cope with this task - it must be replaced. To prevent frequent switching of the recirculation / supply ventilation dampers, a certain hysteresis is provided - with a slight increase in harmful substances, recirculation does not immediately turn 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 / fresh air dampers, the switching requirements "automatic recycling" operates for at least 25 s, even if the concentration of harmful substances decreases so much that the inclusion of recirculation is not necessary. With the air conditioner compressor switched off (for example, when operating in ECON or AC off modes.) maximum duty cycle "automatic recycling" Climatronic control unit -J255- is limited to approx. 15 s. This prevents the windows from fogging up. To defog the windows as quickly as possible, the Climatronic control unit -J255- is set to "Defrosting" blocks recirculation. The air pollution sensor -G238- becomes operational approx. 30 seconds after the ignition is switched on (heating time). During this period, the sensor does not request the Climatronic control unit -J255- to "automatic activation of recirculation". The air pollution sensor -G238- is a highly sensitive electronic assembly which can be damaged by contact with solvents, fuels and certain chemicals. Therefore, sensors that have come into contact with the listed substances should not be installed.
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