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Volkswagen Polo Service & Repair Manual: Checking with Expansion Valve and Receiver/Dryer, with Internally Regulated A/C Compressor

Volkswagen Polo Service & Repair Manual / Refrrigerant R134a Servicing / Pressures, Checking / 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. Refer to → Chapter „Pressures, Checking“.
–  Bring engine speed up to 2000 RPM.
–  Observe manometer battery.
  Note
Switching pressures and design of refrigerant circuit switches are vehicle-specific.
The pressures should be measured at the service connections. The location of these connections is vehicle-specific.
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 in bar (psi)
B -  Low pressure in bar (psi)
C -  Permissible tolerance range
 

Checking with Expansion Valve and Receiver/Dryer, 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 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 the function of the A/C system is not correct after repeating the test, 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 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
If difference in temperature is found at one component:
–  Replace the hose or pipe if kinked or constricted.
–  If there is an obstruction, flush refrigerant circuit with compressed air and nitrogen and replace expansion valve.
If no malfunction can be found.
–  Flush (clean) refrigerant circuit. Refer to → Chapter „Refrigerant Circuit, Flushing (Cleaning) with Refrigerant R134a“.
–  Repeat the test.
 
  Note
If the function is not correct after flushing the refrigerant circuit, the 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
–  Examine expansion valve for dirt or corrosion; replace if necessary.
–  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.
 
  Note
Always replace receiver/dryer in case of this malfunction.
     
Possible deviation from specification Possible cause of fault Corrective action
High pressure normal or too high (see diagram),
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 test
If quantity of refrigerant extracted is substantially greater than specified capacity:
–  Charge the refrigerant circuit.
–  Repeat the test.
 
  Note
If the function of the A/C system is not correct when the test is repeated, re-install old expansion valve and flush refrigerant circuit with compressed air and nitrogen. Then replace 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.
–  Flush (clean) refrigerant circuit. Refer to → Chapter „Refrigerant Circuit, Flushing (Cleaning) with Refrigerant R134a“.
–  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 A/C system function is not OK when the test is repeated, flush (clean) refrigerant circuit. Refer to → Chapter „Refrigerant Circuit, Flushing (Cleaning) with Refrigerant R134a“. Then replace A/C compressor and receiver/dryer.
With this malfunction, evaporator may ice up although 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
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. Refer to vehicle-specific repair manual.
     
Checking with Restrictor and Reservoir, with Internally Regulated A/C Compressor
  Note Connecting service station. Refer to → Chapter „Connecting Service Station“. Observe test requirements ...

Checking with Expansion Valve and Receiver/Dryer, without Regulated A/C Compressor
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