Audi A8 1994 - Page 192

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Note
♦ For the malfunction “high pressure normal, low pressure too
low“ With this malfunction, evaporator may ice up, although
quantity of refrigerant in circuit is OK.
♦ If the problem is with the A/C compressor regulator valve -
N280- (regulator valve is not actuated but A/C compressor
operates nevertheless), refrigerant circuit does not have to be
cleaned (flush with refrigerant R134a, refer to
⇒ “1.4.13 Refrigerant Circuit Flushing With Refrigerant
R134a“, page 32 or blow through using compressed air and
nitrogen, refer to
⇒ “1.4.12 Refrigerant Circuit Flushing With Compressed Air
and Nitrogen “, page 29 ). In this case, it is sufficient to replace
the A/C compressor (observe quantity of refrigerant oil in A/C
compressor).
♦ If expansion valve is malfunctioning (permanently closed or
does not open sufficiently), A/C compressor regulator valve is
actuated to maximum output and low pressure drops to value
in graph or below (compressor draws off refrigerant from low-
pressure side). As however refrigerant cannot flow via expan‐
sion valve, cooling output is not attained and high pressure
may also not increase or only increase slightly due to the ab‐
sence of energy conversion.
♦ Check the measured values from the Evaporator vent tem‐
perature sensor -G263- and the A/C compressor regulator
valve control. If the measured value from the evaporator vent
temperature sensor is incorrect, the evaporator may ice up or
cooling output is not attained. Check using 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).
Possible deviation from speci‐
fication
Possible cause of fault Corrective action
• High pressure normal or too
high
• Low pressure too high (see
graph)
• A/C compressor noise (par‐
ticularly after switch-on)
• The required cooling per‐
formance is obtained
♦ Actuation of A/C compressor regulator
valve -N280- malfunctioning
♦ To much refrigerant in the circuit.
♦ Expansion valve malfunctioning
♦ A/C compressor faulty.
– Check the A/C compressor
regulator valve activation.
– Extract refrigerant from re‐
frigerant circuit
• If quantity of refrigerant ex‐
tracted roughly corresponds
to specified capacity:
– Replace expansion valve
and receiver
– Charge the refrigerant circuit
– Repeat test, if function is not
OK:
– Replace A/C compressor.
• If quantity of refrigerant ex‐
tracted is substantially great‐
er than specified capacity:
– Charge the refrigerant circuit
– Repeat test
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A2 2001 ➤ , A ...
Refrigerant R134a Servicing - Edition 01.2011
188 Rep. Gr.00 - General, Technical Data