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The role of the air conditioning system is not limited
to setting a comfortable temperature for the vehicle’s
occupants. The system also makes an important,
and often neglected, contribution to their safety.
Defrosting / demisting
The heating system also defrosts and demists the
vehicle’s windows, making for better visibility and
improved safety.
g
The design of the air distribution system, and in
particular the layout of the vents and air outlets,
plays a crucial role in keeping the windows, and
especially the side windows, free of mist.
g
The air conditioning system helps to eliminate
mist on the windows.
g
The visibility zones of a windscreen must meet
given standards which are taken into considera-
tion in the vehicle’s design.
Every vehicle shall be equipped with a system for
removing frost and ice from the glazed surfaces of
the windscreen. The windscreen defrosting system
shall be effective enough to ensure adequate visibi-
lity through the windscreen in cold weather.
A’
A
B
Zone A
80%
of surface
defrosted within
20 minutes
80%
of surface
defrosted within
25 minutes
Zone A’
95%
of surface
defrosted within
40 minutes
Zone B
The efficiency of the system shall be verified by
determining the defrosted area of the windscreen
periodically after starting the engine, the vehicle
having been kept in a cold chamber for a certain
amount of time.
g
20 minutes after the start of the test period, the
area A must be 80% defrosted
g
25 minutes after the start of the test period, the
area A’ (passenger side) must be 80% defrosted
g
40 minutes after the start of the test period, the
area B must be 95% defrosted
Electric heated windscreens are a good example of
how defrost time and visibility can be perfected.
They have an immediate effect and they do not im-
pair the occupants’ comfort since they are silent and
do not generate strong air flows.
But they remain relatively rare, except in cold climates,
and their use also depends on the levels of comfort
proposed to customers.
Air conditioning
comfort and
safety
7
Regulations applying to defrosting zones, as per the
standard 78/317 CEE (Europe).
Defrost regulation
15