Volkswagen Golf Service & Repair Manual: Function of air quality sensor -G238-
| The air quality sensor detects noxious substances in the
ambient air (primarily petrol and/or diesel fumes). |
| The Climatronic control unit -J255- evaluates the signal
from the air quality sensor -G238-. The air conditioning system
is activated depending on the degree and manner of ambient air
pollution. |
| At an ambient temperature higher than approx. +2 °C, air
recirculation is activated even when there is a minimal increase
in noxious substances in the ambient air. |
| At an ambient temperature between approx. +2 °C and approx.
–5 °C, air recirculation is not activated until there is a
strong increase in noxious substances in the ambient air. The
air conditioner compressor is also activated at the same time. |
| At an ambient temperature less than approx. –5 °C, air
recirculation is not activated until there is a strong increase
in noxious substances in the outside air, but only for approx.
15 seconds, and the air conditioner compressor is not activated.
When the concentration decreases, the air conditioning system is
switched back to fresh air mode. |
| The “automatic recirculation mode” can be switched off at
any time. If the function is active, the air conditioner
compressor will be switched on even at an ambient temperature
below +2 °C when “automatic recirculation mode” is required.
However, even with this function, it is not possible to operate
the air conditioner compressor at temperatures below approx.
–5 °C. |
| On vehicles with “automatic recirculation mode”, the air
conditioner compressor can also be switched on at temperatures
down to approx. –5 °C even if the air recirculation mode has
been activated manually. |
| So that the air conditioning system does not operate
continually in air recirculation mode in areas with consistently
high levels of pollutants, the "intelligent" sensor adapts its
sensitivity to the prevailing environmental pollution. |
| If the level of noxious substances in the ambient air
remains relatively high over a long period of time, the
intelligent sensor starts to adapt to the change in
environmental conditions so that, generally, the demand for
recirculated air lasts less than 12 minutes in areas where the
ambient air exhibits a constant level of pollution. If a series
of pollution peaks occur, the air conditioning system may
operate over a longer period of time in air recirculation mode. |
| A certain amount of time is required for repositioning of
the air conditioning system flaps. To prevent noxious substances
from entering the passenger compartment while the flaps are
closing (e.g. when driving through a cloud of diesel smoke), a
dust and pollen filter with an activated charcoal layer is
installed. A saturated filter cannot perform this task and
should be renewed. |
| To prevent too frequent operation of the recirculation/fresh
air flap, the flap is not actuated immediately if there is a
minimal increase in noxious substances in the ambient air (the
sensor does not send a request to the Climatronic control unit
-J255-). The effect of the activated charcoal filter in the dust
and pollen filter is adequate for this. |
| To prevent the air recirculation/fresh air flap from
switching too frequently, the sensor's request for “automatic
recirculation” continues for at least 25 seconds (minimum
waiting period) even if the air pollutants decrease to a level
that no longer requires air recirculation. |
| If the air conditioner compressor is switched off (AC
button is deactivated), the maximum time assigned to the
“automatic recirculation mode” is limited to approx. 15 seconds
by the Climatronic control unit -J255- so that condensation does
not develop on the windows. |
| To clear condensation from windows as quickly as possible,
the Climatronic control unit -J255- does not permit air
recirculation when the “defrost function” is activated. |
| The air quality sensor -G238- requires approx. 30 seconds to
become operational once the ignition has been switched on
(warm-up time). During this time, the sensor can send no request
for “automatic recirculation mode” to the Climatronic control
unit -J255-. |
| The air quality sensor -G238- is a highly sensitive
electronic component which could be destroyed by direct contact
with solvents, fuels and certain chemical compounds. For this
reason, do not install sensors that may have come into contact
with these substances. |
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Special tools and workshop equipment
required
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