Audi Q5 2008 - Page 158

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Under certain operating conditions, residual moisture in refriger‐
ant circuit can lead to an ice build-up at compressor regulator
valve. A/C compressor control is reduced by this ice build-up,
evaporator is cooled too intensely and freezes. The freeze-up of
the evaporator can be the cause for the following customer com‐
plaints:
♦ After a long drive, A/C system repeatedly or sporadically fails
(no cooling or heating performance), after switching off vehicle
and after a short time, A/C function is OK again.
♦ After a long drive, windows fog up from inside, windows are
also not cleared by then pressing the Defrost button, after
switching off vehicle and after a short time, A/C function is OK
again.
Corrective Action
– On vehicles as of model year 2001 equipped with a compres‐
sor with A/C compressor regulator valve -N280- , check meas‐
ured value of evaporator outflow temperature Evaporator vent
temperature sensor -G263- (via function “Read measuring
value block“). Is the measured value from the sensor below
the operating condition described by the customer (at a tem‐
perature above 0° C, longer when it is lower than 0° C although
the A/C compressor regulator valve is not currently activated)
or too high (above 10° C even though the A/C is working cor‐
rectly). An incorrect measured value can cause the evaporator
to ice up. Refer to Vehicle Diagnosis, Testing & Information
System -VAS5051B- (“OBD“ or “Guided Fault Finding for the
A/C system“) and ⇒ Heating, Ventilation and Air Conditioning;
Rep. Gr. 87 ; Diagnosis and Testing (vehicle-specific repair
manual).
– If the vehicle does have an Evaporator vent temperature sen‐
sor -G263- , check the "Lo temperature" for driver and pas‐
senger side, 4 or 5 bars for fresh air blower RPM, air outlet in
footwell and fresh air operation under operating conditions
specified by customer, for example, using the Footwell vent
temperature sensor -G192- . If measured value of sensor is
too low (at ambient temperature above 0 °C, colder than 0 ℃
for a long period of time).
– Check refrigerant line from evaporator to accumulator (thick
tube, low pressure side) with engine running. If this line is
thickly iced-up when complaint occurs (a thin layer of ice is
permitted), this also indicates that the temperature in the evap‐
orator is too low.
– Discharge refrigerant circuit, replace accumulator or fluid res‐
ervoir with dryer and evacuate refrigerant circuit for a minimum
of 3 hours.
♦ Test requirements, refer to
⇒ “4.4.2 Test Prerequisites“, page 154 .
♦ Pressures, checking, refer to
⇒ “4.4.3 Pressures, Checking “, page 156 .
♦ Continuation of testing depending on design of refrigerant cir‐
cuit, refer to ⇒ page 158 .
4.4.2 Test Prerequisites
• Radiator and condenser are clean (clean if necessary)
• Thermal insulation at expansion valve OK and properly instal‐
led.*
• Ribbed belt is OK and properly tensioned. Ribbed belt for A/C
compressor and generator are OK and correctly tensioned.*
• All air ducts, covers and seals OK and properly installed
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A2 2001 ➤ , A ...
Refrigerant R134a Servicing - Edition 01.2011
154 Rep. Gr.00 - General, Technical Data