Audi Air conditioning 2003 A8 Workshop Manual page 18

Audi A8 2003 ➤
Air conditioning - Edition 09.2010
3.3.2 Pressure signal from high-pressure
sender -G65-
-A- Pressure on high-pressure end of refrigerant circuit in bar
(absolute)
-B- Ratio of square-wave signal
-C- Characteristic curve
Note
As soon as there are no compressor shut-off criteria, the front
♦
operating and display unit, Climatronic control unit -J255-
switches on the compressor (by actuating the air conditioner
compressor regulating valve -N280- ):
The signal generated by the high-pressure sender -G65- is
♦
also used for engine control. The front operating and display
unit, Climatronic control unit -J255- transmits the information
via the convenience data bus system to the engine control unit
(the torque required for driving the compressor is governed by
the pressure in the refrigerant circuit). Depending on the ver‐
sion of the engine control unit, the signal is displayed as a ratio
in the measured value block ⇒ "Guided fault-finding" function
of vehicle diagnostic, testing and information system
VAS 5051 (for engine control unit)
♦ The pressure in the refrigerant circuit is OK (the front operating
and display unit, Climatronic control unit -J255- does not de‐
tect any compressor shut-off criteria)
– If the ratio is greater than 12 % (corresponding to approx. 1.8
bar absolute) and less than 87.5% (corresponding to approx.
32 bar absolute)
Note
If the signal ratio is less than 12 % or greater than 87.5%, the
♦
compressor is not switched on (the air conditioner compressor
regulating valve -N280- is not actuated).
The signal ratio and the pressure calculated by the front op‐
♦
erating and display unit, Climatronic control unit -J255- are
indicated in the measured value block ⇒ "Guided fault-finding"
function of vehicle diagnostic, testing and information system
VAS 5051.
At absolute pressure, 0 bar corresponds to an absolute vac‐
♦
uum. Normal ambient pressure thus corresponds to roughly 1
bar absolute. On the scales of most pressure gauges, 0 bar
corresponds to an absolute pressure of one bar (can be seen
from -1 mark below 0).
♦ The front operating and display unit, Climatronic control unit -
J255- transmits the request for radiator fan actuation via the
convenience data bus system to the engine control unit, which
then switches on the radiator fan by way of the fan control unit:
– Irrespective of the pressure in the refrigerant circuit as soon
as the compressor is switched on
12
Rep. gr.87 - Air conditioning system
Protected by copyright. Copying for private or commercial purposes, in part or in whole, is not
permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.