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Specified Values For The Refrigerant Circuit Pressures

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High-Pressure Side:

Increasing from initial pressure (when connecting the pressure gauges) to a maximum of 20 bar (290.08 psi).

Low-Pressure Side:

Decreasing from initial pressure (when connecting pressure gauges) to the value in the graph.

Fig 1: Identifying Permissible Tolerance Range Graph
GWWA87-0006Courtesy of AUDI OF AMERICA, LLC

A -High Pressure (Measured at Service Connection) in Bar

B -Low pressure (measured at connection with valve at compressor or accumulator) in bar.

C -Permissible Tolerance Range

D -Low Pressure (Measured at Connection with Valve for Low-Pressure Switch or at Service Connection) in Bar

E -Permissible Tolerance Range

Possible deviation from specification Possible cause of fault Corrective action
  • High pressure remains constant or increases only slightly (above pressure with engine stopped),
  • Low pressure quickly drops to value in graph or below
  • The requested cooling output is not attained.
 Not enough refrigerant in refrigerant circuit. -- Localize leak with leak detector and eliminate.-- Charge the refrigerant circuit.
  • High pressure normal
  • Low pressure in line with value in graph,
  • The requested cooling output is not attained.
    
  • High pressure normal
  • Low pressure too low (see graph),
  • The requested cooling output is not attained.
    
NOTE:

If no error is detected with this complaint, clean the refrigerant circuit (by flushing with refrigerant R134a, refer to Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or clean using compressed air and nitrogen, refer to Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ).

Possible deviation from specification Possible cause of fault Corrective action
  • High pressure does not increase or only increases slightly above pressure with engine stopped.
  • Low pressure does not drop or drops only slightly.
  • The requested cooling output is not attained.
  • The A/C compressor does not activate (the A/C clutch).
  • The A/C compressor is not being driven.
 -- Check and service the A/C compressor activation and motor. Refer to A/C Compressor (vehicle-specific Service Information).
 
  • Constriction or obstruction in refrigerant circuit (for example, inside the refrigerant line between the service connection "low pressure side" and the A/C compressor).
 -- Clean the refrigerant circuit by flushing with refrigerant R134a (refer to Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ) or blow through using compressed air and nitrogen (refer to Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ).-- Replace the hose or pipe if kinked or constricted.
 
  • A/C compressor faulty.
 -- Replace the A/C compressor.
Possible deviation from specification Possible cause of fault Corrective action
  • High pressure increases above specification
  • Low pressure quickly drops to value in graph or below
  • The requested cooling output is not attained.
 Constriction or obstruction in refrigerant circuit. -- Run hand over refrigerant circuit to check for differences in temperature. Refer to Refrigerant Circuit (vehicle-specific Service Information).
  • If difference in temperature is found at one component:
-- Replace the hose or pipe if kinked or constricted.-- In the event of an obstruction, clean refrigerant circuit by flushing with refrigerant R134a (refer to Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ), or blowing through with compressed air and nitrogen (refer to Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ).
  • If no malfunction can be found:
-- Clean the refrigerant circuit by flushing with refrigerant R134a (refer to Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ) or blow through using compressed air and nitrogen (refer to Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ).
  • High and low pressure normal at first after some time,
  • High pressure increases above specification,
  • Low pressure quickly drops to value in graph or below,
  • Required cooling output is no longer attained.
 Moisture in refrigerant circuit -- Check the reservoir (with dryer) and restrictor and replace if necessary. Then evacuate the refrigerant circuit for a minimum of three hours (see note).-- Clean the refrigerant circuit by flushing with refrigerant R134a (refer to Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ) or blow through using compressed air and nitrogen (refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ).
  • High and low pressure normal at first.
  • After lengthy operating period, the low pressure drops excessively (evaporator ices up).
    
NOTE:

If problem involving moisture in refrigerant circuit only occurs after a lengthy operating period or only infrequently (low pressure drops below specification and evaporator ices up), it is sufficient to replace the dryer (adjust quantity of refrigerant oil). Refrigerant circuit is then to be evacuated for at least three hours.

It is not initially necessary to clean the refrigerant circuit by flushing using refrigerant R134a (refer to Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ) or blow through using compressed air and nitrogen (refer to Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ) when this problem occurs since normally, there is only a small quantity of moisture in the system which can be removed by lengthy evacuation.

Possible deviation from specification Possible cause of fault Corrective action
  • High pressure normal
  • Low pressure too low (see graph),
  • The required cooling performance is obtained.
 A/C compressor faulty. -- Clean the refrigerant circuit by flushing with refrigerant R134a (refer to Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ) or blow through using compressed air and nitrogen (refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ).-- Replace the A/C compressor.
NOTE:

For the fault "high pressure normal, low pressure too low", note the following: With this fault, it may be that the evaporator is icing up or the A/C Refrigerant Low Pressure Switch -F73- is turning off the A/C compressor, although the refrigerant quantity in the circuit is OK.

For the Audi 100, Audi A6 (through and including MY 1997) and Audi V8, this fault may result in the A/C compressor being shut off by the display control head (if the temperature at fresh air blower drops below -3 °C (26.6 °F)). Refer to Refrigerant Circuit (vehicle-specific Service Information) or Component Location Overview - A/C System (vehicle-specific Service Information).

Possible deviation from specification Possible cause of fault Corrective action
  • High pressure normal or too high,
  • Low pressure too high (see graph),
  • A/C compressor noise (particularly after switch-on),
  • The requested cooling output is not attained.
 Too much refrigerant in the circuit. -- Extract refrigerant from the refrigerant circuit.
  • If the quantity of refrigerant extracted roughly corresponds to specified capacity:
-- Replacing the A/C compressor.
  • If the quantity of refrigerant extracted is substantially greater than specified capacity:
-- Charge the refrigerant circuit.-- Repeat the test.
Possible deviation from specification Possible cause of fault Corrective action
  • High and low pressure normal,
  • The requested cooling output is not attained.
 Too much refrigerant oil in the circuit. -- Discharge the refrigerant circuit.-- Clean the refrigerant circuit by flushing with refrigerant R134a (refer to Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ) or blow through using compressed air and nitrogen (refer to Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ).
  • High and low pressure normal,
  • A/C compressor noise (particularly after switch-on),
  • The required cooling performance is obtained.
    
NOTE:

Overfilling with refrigerant oil can occur if, for example, the compressor has been replaced without adjusting the quantity of refrigerant oil.

If there is too much refrigerant oil in the circuit, the A/C compressor must be discharged and the reservoir must be replaced. After cleaning the refrigerant circuit by flushing with refrigerant R134a (refer to Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ), or blowing through using compressed air and nitrogen (refer to Refer to REFRIGERANT CIRCUIT, CLEANING WITH COMPRESSED AIR AND NITROGEN ) fill the circuit with the correct quantity of refrigerant oil. Refer to Refer to APPROVED REFRIGERANT OILS AND REFRIGERANT OIL CAPACITIES .

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