Audi Q7 2007 Repair Manual page 235

13.3.2 Rear Cooling Output, Checking
Note
If there is a complaint at only the evaporator in rear A/C unit
♦
on vehicles with two evaporators, first perform cooling per‐
formance testing at front A/C system. Refer to
⇒ "13.2 Front A/C System, Testing Cooling Performance",
page 215 . If cooling performance at front is OK, check cooling
performance at rear A/C system. If, during cooling perform‐
ance testing on rear A/C system, it is detected that perform‐
ance is not sufficient and then no cause for the complaint can
be found, check line connection between evaporator in ques‐
tion and exit of line connection at distribution point of refriger‐
ant lines in left front wheel housing (for example, for
constriction). If the fault cannot be found, bring the vehicle to
a workshop that has the necessary tools and in which the work
can be performed accordingly by qualified personnel (there is
a problem in the refrigerant circuit). Refer to ⇒ Refrigerant
R134a Servicing; Rep. Gr. 87 ; A/C System General Informa‐
tion (A/C System with Refrigerant R134a; A/C System, Gen‐
eral Information).
There is no sensor that measures air temperature downstream
♦
of evaporator installed in the rear A/C unit, compressor per‐
formance control is performed therefore only via the measured
value of the Evaporator Vent Temperature Sensor - G263- ,
which is installed in the front A/C unit. Under certain unfavor‐
able conditions, it may occur therefore because of this that the
temperature set on the rear A/C unit is not attained during
normal regulated operation even though the A/C system is OK.
Also it may occur that, for example, on an A/C system on which
the specified outflow temperature has already been attained
in the front A/C unit and maximum cooling output is requested
at rear A/C system, the rear outflow temperature is a few de‐
grees° C higher than when a high cooling output is requested
at front A/C system (if necessary increase front cooling output
via setting at front).
– Perform test of front cooling performance. Refer to
⇒ "13.2.2 A/C System Cooling Performance, Checking", page
217 .
Note
The measured values of temperature sensors ( Left Rear Vent
♦
Temperature Sensor - G405- and Right Rear Vent Tempera‐
ture Sensor - G406- ) installed in air duct are evaluated for
cooling performance test of rear A/C system. By using these
measured values, it is then not necessary to remove compo‐
nents for the test.
For the cooling performance test at front and rear, the same
♦
Protected by copyright. Copying for private or commercial purposes, in part or in whole, is not
settings on the Climatronic Control Module - J255- front A/C
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.
control head and on the Rear A/C Display Control Head -
E265- are required ("Auto" operating mode, temperature pre‐
select "Lo").
– Initiate the On Board Diagnostic (OBD) for the Rear A/C Dis‐
play Control Head - E265- of A/C system. Use the Vehicle
Diagnostic Tester via the "Guided Fault Finding" function.
– In the Rear A/C Display Control Head - E265- , select "read
measured values block" the display group with the measured
values from the Left Rear Vent Temperature Sensor - G405-
and Right Rear Vent Temperature Sensor - G406- . Use the
Heating, Ventilation and Air Conditioning - Edition 04.2013
Audi Q7 2007 ➤
13. A/C Unit, Checking Cooling Output
229