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with respect to the correctness of information in this document. Copyright by AUDI AG.
Note
♦
As soon as there are no conditions for switching off the A/C
compressor, the Climatronic control module -J255- switches
the A/C compressor on (by activating the A/C compressor reg‐
ulator valve -N280- ). Refer to Vehicle diagnosis, testing and
information system -VAS5051B- in "Guided Fault Finding".
♦
The Climatronic control module switches the compressor on
at a duty cycle larger than approximately 12% (corresponds to
approximately 1.2 bar absolute pressure) and less than ap‐
proximately 78% (corresponds to approximately 32 bar abso‐
lute pressure), if no other shut off criterion is in effect.
♦
The compressor is not switched on if the duty cycle is smaller
than 12% or greater than 78% ( the Compressor Regulator
Valve -N280- is not activated).
♦
The duty cycle and pressure calculated by the Climatronic
control module is displayed in the measured value block. Refer
to Vehicle diagnosis, testing and information system -
VAS5051B- under "Guided Fault Finding".
♦
In terms of absolute pressure, 0 bar corresponds to an abso‐
lute vacuum. Normal ambient pressure equals approximately
1 bar absolute pressure. 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 Climatronic control module sends the calculated refriger‐
ant circuit pressure vie the Data bus. When the A/C compres‐
sor is activated, the coolant fan -V7- requests the engine
control module for increased RPM's, and activates the coolant
fan directly or via the Coolant fan control module -J293- . De‐
pending on version with a certain pressure in the refrigerant
circuit or not depending on pressure as soon as the A/C com‐
pressor is switched on. The request from the Climatronic
control moduled is displayed in the measuring value block.
Refer to Vehicle diagnosis, testing and information system -
VAS5051B- under "Guided Fault Finding".
♦
The request to activate the coolant fan is currently only sent
to the databus system by the Climatronic control module at a
specified pressure in the refrigerant circuit. If the pressure in
the refrigerant circuit is greater than approximately 9 bar (6
bar, if the pressure was previously greater than 9 bar) and less
than 20 bar, a request from 30 to 100 % takes place, depend‐
ing on pressure.
♦
If the pressure in the refrigerant circuit is less than 9 bar (6 bar
if the pressure was greater than 9 bar before), there is no re‐
quest at this time to activate the coolant fan from the Clima‐
tronic control module.
♦
If the pressure in the refrigerant circuit is greater than approx‐
imately 20 bar, there is no request at this time to activate the
coolant fan from 100% from the Climatronic control module
(depending on the version of the engine control module/ Cool‐
ant fan control module -J293- , the actual activation may be
less than 100%).
♦
The signal generated from high pressure sensor is also used
to control the engine. The Climatronic control module sends
the information to the Engine Control Module (ECM) via the
databus system (the necessary torque to drive the A/C com‐
pressor depends on the pressure in the refrigerant circuit).
Depending on the version of the engine control module, the
signal in the measured values block will be displayed as a duty
cycle. Check using Vehicle diagnosis, testing and information
system -VAS5051B- under "Guided Fault Finding", (the A/C
system and, depending on engine, the fuel injection and igni‐
tion system or the diesel direct injection and glow plug sys‐
tem).
♦
Depending on the version of the high pressure sensor, an in‐
sufficient measuring value for the pressure in the refrigerant
system will be sent by the high pressure sensor at low outside
temperatures (lower than 5 °C) (even though the A/C system
is OK and the refrigerant circuit is properly filled). At lower out‐
side temperatures (ambient temperature lower than 5 °C), —
the Climatronic control module with part number “8J0 820 043“
through to index “AJ“—might therefore make an incorrect DTC
memory entry (DTC memory entry: high pressure sensor “,
and fall below the lower threshold“). If the fault is displayed as
a sporadic fault at an outside temperature greater than 5 °C,
calculated by the A/C system, and if the A/C function is OK,
then clear the DTC memory (no additional steps are neces‐
sary). This error does not occur with — the Climatronic control
module, part number “8J0 820 043“ beginning with index “AK“.
Audi TT 2007 ➤
Heating, Ventilation and Air Conditioning - Edition 01.2011
2. Description and Operation 73
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