ABS ESP AUDI A8 2003 D3 / 2.G Technical Features Manual

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Humidity sender G355
Heating/Air Conditioner
At low ambient temperatures, when the
windscreen is extremely cold, the top third is
particularly susceptible to fogging.
To cover this area, the humidity sender G355
is fitted in front of the base of the rear view
mirror.
The sender is designed to detect the
following:
– Humidity level
– Sender ambient temperature and
– Windscreen temperature
All three functions are combined in the
sender housing.
The humidity sender is intended for all
equipment versions.The sender data enable the air conditioning
system to detect potential misting of the
windscreen in good time.
Before water vapour from the air in the
passenger compartment can form on the
windows, the output of the air conditioner
compressor and the blower speed are
automatically increased and the defrost flap
is opened further. Dry air is then routed from
the open defrost vents to the windscreen and
side windows via the evaporator and heat
exchangers.
Measurement of humidity level and
corresponding temperature
Physical principles
Humidity measurement involves determining
the water vapour content of the passenger
compartment air. The capacity of air to
absorb water vapour is governed by the air
temperature. It is thus necessary to
determine not only the humidity level but also
the corresponding air temperature in the
measurement area.The warmer the air, the more water vapour it
can absorb. Water starts to condense if this
water-vapour enriched air cools down again.
This results in fine droplets forming on the
windscreen.
SSP282_104