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Volkswagen Polo Service & Repair Manual: Checking with Restrictor and Reservoir, with Internally Regulated A/C Compressor

Volkswagen Polo Service & Repair Manual / Refrrigerant R134a Servicing / Pressures, Checking / Checking with Restrictor and Reservoir, with Internally Regulated A/C Compressor

  Note
Connecting service station. Refer to → Chapter „Connecting Service Station“.
Observe test requirements. Refer to → Chapter „Pressures, Checking“.
–  Bring engine speed up to 2000 RPM.
–  Pay attention to the A/C service station pressure gauge.
  Note
Switching pressures for refrigerant circuit switches are vehicle-specific.
Connection with valve for low-pressure switch or at evaporator is only to be used for vehicles with no service connection on low-pressure side and inaccessible connection at compressor or accumulator (measurement accuracy). Only applies to certain vehicles.
Refer to → Rep. Gr.87.
Specified Values
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.
A -  High pressure (measured at service connection) in bar (psi)
B -  Low pressure (measured at connection with valve at compressor or accumulator) in bar (psi).
C -  Permissible tolerance range
D -  Low pressure (measured at connection with valve for low-pressure switch or at service connection) in bar (psi)
E -  Permissible tolerance range
 

Checking with Restrictor and Reservoir, with Internally Regulated A/C Compressor

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 refrigerant circuit
–  Check for leaks and correct.
–  Charge the refrigerant circuit.
High pressure normal
Low pressure in line with value in graph
Required cooling output is not attained
   
High pressure normal
Low pressure too low (see graph)
Required cooling output is not attained
   
 
  Note
If no malfunction is found with this complaint, flush (clean) refrigerant circuit with refrigerant R134a. Refer to → Chapter „Refrigerant Circuit, Flushing (Cleaning) with Refrigerant R134a“. If that is not possible in this workshop, flush the refrigerant circuit with compressed air and remove moisture with nitrogen. Refer to → Chapter „Refrigerant Circuit, Flushing with Compressed Air and Nitrogen“.
     
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.
–  Flush (clean) refrigerant circuit. Refer to → Chapter „Refrigerant Circuit, Flushing (Cleaning) with Refrigerant R134a“.
–  Replace 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
–  Run hand over refrigerant circuit to check for differences in temperature
If difference in temperature is found at one component:
–  Replace the hose or pipe if kinked or constricted.
–  In the event of an obstruction, flush refrigerant circuit with compressed air and nitrogen
–  Repeat test if function is not OK.
–  Flush (clean) refrigerant circuit. Refer to → Chapter „Refrigerant Circuit, Flushing (Cleaning) with Refrigerant R134a“.
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
–  Flush refrigerant circuit with compressed air and nitrogen.
–  Replace receiver/dryer.
–  Repeat test if function is not OK.
–  Flush (clean) refrigerant circuit. Refer to → Chapter „Refrigerant Circuit, Flushing (Cleaning) with Refrigerant R134a“.
–  Charge the refrigerant circuit.
–  Repeat the test.
High pressure normal
Low pressure too low (see graph)
The required cooling performance is obtained
A/C compressor faulty.
–  Flush (clean) refrigerant circuit. Refer to → Chapter „Refrigerant Circuit, Flushing (Cleaning) with Refrigerant R134a“.
–  Replace A/C compressor.
 
  Note
For the malfunction “high pressure normal, low pressure too low”, note the following:
This fault may cause the evaporator to ice up or the A/C Refrigerant Low Pressure Switch -F73- to shut off the compressor although the amount of refrigerant in the circuit is OK.
     
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)
Required cooling output is not attained
Too much refrigerant in the circuit.
–  Extract refrigerant from the refrigerant circuit
If quantity of refrigerant extracted roughly corresponds to specified capacity:
–  Replace the A/C compressor.
If 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
Required cooling output is not attained
To much refrigerant oil in the circuit.
–  Discharge the refrigerant circuit.
–  Flush (clean) refrigerant circuit. Refer to → Chapter „Refrigerant Circuit, Flushing (Cleaning) with Refrigerant R134a“.
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 in the event, for example, the compressor has been replaced without adjusting the quantity of refrigerant oil.
If the A/C compressor is not replaced, the refrigerant oil should be drained from the A/C compressor via the oil drain plug. Out of the entire quantity of refrigerant oil, 50 grams should be put in the A/C compressor and the rest in the refrigerant circuit.
     
Compressor Types, Checking Pressures
  Note Check cooling performance. The A/C system is functioning correctly when the air flowing from the instrument panel vents has a temperature of ...

Checking with Expansion Valve and Receiver/Dryer, with Internally Regulated A/C Compressor
  Note Connecting service station. Refer to → Chapter „Connecting Service Station“. Observe test requirements ...

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