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Home >> Audi >> 2021 >> A4 Quattro Premium Plus, 2.0L Eng VIN B >> Repair and Diagnosis >> Heating, Ventilation & A/C (HVAC) >> General Servicing >> Air Conditioning (Refrigerant R134A Servicing) (1 Of 2) >> 87 Air Conditioning >> Pressures, Checking >> Checking Pressures On Vehicles With Expansion Valve And Receiver/Dryer (With Internally Regulated Compressor) >> Specified Values For The Refrigerant Circuit Pressures

Specified Values For The Refrigerant Circuit Pressures

High-Pressure Side:

Increasing from initial pressure (when connecting the pressure gauges) to a maximum of 20 bar (290 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
GWWA87-0146Courtesy of AUDI OF AMERICA, LLC

A -  High pressure in bar (psi)

B -  Low pressure in bar (psi)

C -  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
  • Required cooling output is not attained
 Not enough refrigerant in circuit or expansion valve malfunctioning. -- Extract refrigerant from the refrigerant circuit
  • If quantity of refrigerant extracted roughly corresponds to specified capacity:
-- Replace expansion valve-- Charge the refrigerant circuit.-- Repeat the test.
  • High pressure normal
  • Low pressure in line with value in graph
  • Required cooling output is not attained
  
  • If quantity of refrigerant extracted is substantially less than specified capacity:
-- Localize the leak with leak detector and eliminate-- Charge the refrigerant circuit.-- Repeat the test.
NOTE:

If no malfunction can be found and air conditioner operation is not OK when test is repeated, clean refrigerant circuit (flush using refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blow through using compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING 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.
  • Required 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 drive. Refer to A/C Compressor .
 
  • 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 (flush with refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blow through with compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN ).-- Replace the hose or line 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
  • Required cooling output is not attained
  • Constriction or obstruction in refrigerant circuit
  • Expansion valve faulty
 -- Run hand over refrigerant circuit to check for differences in temperature. Refer to SYSTEM OVERVIEW - REFRIGERANT CIRCUIT .
  • If difference in temperature is found at one component:
-- Replace the hose or line if kinked or constricted.-- In the event of an obstruction, clean the refrigerant circuit (flush with refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blow through with compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN ; and replace expansion valve if necessary)
  • If no malfunction can be found:
-- Clean the refrigerant circuit (flush with refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blow through with compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN ; and replace expansion valve if necessary).-- Repeat the test.
NOTE:

If operation is not OK after cleaning refrigerant circuit (flushing with R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blowing through using compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN ), expansion valve must be replaced.

Possible Deviation from Specification Possible Cause of Fault Corrective Action
  • High and low pressure normal at first
  • After some time, high pressure increases above specification and low pressure drops to value in graph or below
  • Required cooling output is no longer attained.
  • Expansion valve faulty
  • Moisture in refrigerant circuit
 -- Replace the receiver/dryer (with dryer) and evacuate the refrigerant circuit for a minimum of three hours. Refer to the notes below.-- Examine expansion valve for dirt or corrosion; replace if necessary.-- Clean the refrigerant circuit (flush with refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blow through with compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING 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:

It is not initially necessary to clean the refrigerant circuit (flush using refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blow through using compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING 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.

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.

Possible Deviation from Specification Possible Cause of Fault Corrective Action
  • High pressure normal or too high
  • Low pressure too high (see graph)
  • Required cooling output is not attained,
  • A/C compressor noise (particularly after switch-on).
  • Too much refrigerant in the circuit.
  • Expansion valve or A/C compressor faulty.
 -- Extract refrigerant from the refrigerant circuit
  • If quantity of refrigerant extracted roughly corresponds to specified capacity:
-- Replace expansion valve-- Charge the refrigerant circuit.-- Repeat the test.
  • If quantity of refrigerant extracted is substantially greater than specified capacity:
-- Charge the refrigerant circuit.-- Repeat the test.
NOTE:

If air conditioner operation is not OK when test is repeated, install old expansion valve, clean refrigerant circuit (flush using refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blow through using compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN ). Then replace the A/C compressor and receiver/dryer.

Possible Deviation from Specification Possible Cause of Fault Corrective Action
  • High pressure only increases slightly above pressure with engine stopped
  • Low pressure drops only slightly
  • Required cooling output is not attained
 A/C compressor faulty. -- Clean the refrigerant circuit (flush with refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blow through with compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN ).-- Replace A/C compressor and receiver/dryer.
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.
 Expansion valve or A/C compressor faulty. -- Replace expansion valve-- Charge the refrigerant circuit.-- Repeat the test.
NOTE:

If air conditioner operation is not OK when test is repeated, install old expansion valve, clean refrigerant circuit (flush using refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blow through using compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN ). Then replace the A/C compressor and receiver/dryer.

With this malfunction, evaporator may ice up although the quantity of refrigerant in circuit is OK.

Possible Deviation from Specification Possible Cause of Fault Corrective Action
  • High and low pressure normal
  • Required cooling output is not attained
 Too much refrigerant oil in the circuit. -- Discharge the refrigerant circuit.-- Clean the refrigerant circuit (flush with refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blow through with compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING 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 compressor must be drained and the receiver/dryer must be replaced. After cleaning the refrigerant circuit (flushing with refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blowing through using compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN ), the correct quantity of refrigerant oil is filled into the circuit. Refer to REFRIGERANT R134A CAPACITIES, REFRIGERANT OIL AND APPROVED REFRIGERANT OILS .

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