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Working with the A/C service station > < Checking pressures on vehicles

Leon Mk1

Specifications:
Specifications:
High-pressure side:
From initial pressure (upon connecting the manometer) increasing to a maximum of 20 bar positive pressure.
Low-pressure side:
   
From initial pressure (upon connecting the manometer) decreasing to the diagram value.
A - High pressure in bar positive pressure.
B - Low pressure in bar positive pressure.
C - Permitted tolerance range.
  A87-0146
Possible deviation from specificationPossible cause of faultRectifying fault
l  High pressure remains constant or increases only slightly (above the pressure measured when the engine is stopped),
l  Low pressure falls quickly to the diagram value or lower,
l  the required cooling power is not delivered.
Too little refrigerant in circuit or expansion valve defective.
–  Extract some refrigerant from the refrigerant circuit.
l  The quantity of refrigerant extracted is about equal to the prescribed charge quantity.
–  Renew expansion valve.
–  Recharge refrigerant circuit.
–  Repeat check.
l  High pressure normal,
l  Low pressure matches the diagram value,
l  the required cooling power is not delivered.
 
l  The quantity of refrigerant extracted is significantly less than the prescribed charge quantity.
–  Look for leaks using leak detector and rectify them.
–  Recharge refrigerant circuit.
–  Repeat check.

  Note!
If no fault can be determined and the function of the air conditioning system is not OK when the test is repeated, flush refrigerant circuit with compressed air and nitrogen.
   
Possible deviation from specificationPossible cause of faultRectifying fault
l  High pressure increases beyond the specification,
l  Low pressure falls quickly to the diagram value or lower,
l  the required cooling power is not delivered.
t  Restriction or obstruction in the refrigerant circuit.
t  Expansion valve defective.
–  Feel the refrigerant circuit with the hand to sense the temperature gradient.
l  At one component a temperature gradient will be detected:
–  If a hose or pipe is kinked or crushed, renew it.
–  In case of an obstruction, flush refrigerant circuit with compressed air and nitrogen and renew expansion valve.
l  If no faults are found:
–  Rinse (clean) refrigerant circuit → Chapter.
–  Repeat check.

  Note!
If the air conditioning system is still not operating correctly after the refrigerant circuit has been purged with compressed air and nitrogen, the expansion valve must be renewed.
   
Possible deviation from specification Possible cause of faultRectifying fault
l  High pressure and low pressure are normal at first,
l  after a while, the high pressure increases beyond the specification, and the low pressure falls to the diagram value or lower,
l  the cooling power called for is not delivered.
t  Expansion valve defective.
t  Moisture in the refrigerant circuit.
–  Examine the expansion valve for dirt or corrosion; renew if necessary.
–  Flush refrigerant circuit with compressed air and nitrogen.
–  Renew receiver.
–  Repeat the check; if the system does not operate correctly
–  Rinse (clean) refrigerant circuit → Chapter.
–  Recharge refrigerant circuit.
–  Repeat check.

  Note!
When this fault occurs, always renew receiver.
   
Possible deviation from specification Possible cause of faultRectifying fault
l  High pressure normal or too high (see diagram),
l  the required cooling power is not delivered.
l  The air conditioner compressor is noisy (especially immediately after being switched on),
t  Too much refrigerant in circuit.
t  Expansion valve or air conditioner compressor defective.
–  Extract some refrigerant from the refrigerant circuit.
l  The quantity of refrigerant extracted is about equal to the prescribed charge quantity.
–  Renew expansion valve.
–  Recharge refrigerant circuit.
–  Repeat test.
l  The quantity of refrigerant extracted is significantly greater than the prescribed charge quantity.
–  Recharge refrigerant circuit.
–  Repeat check.

  Note!
If the air conditioning system is still not operating correctly when the test is repeated, refit the expansion valve and flush the refrigerant circuit with compressed air and nitrogen. Then renew the air conditioner compressor and receiver.
   
Possible deviation from specificationPossible cause of faultRectifying fault
l  High pressure increases only slightly above the pressure measured when the engine is stopped,
l  Low pressure falls only slightly,
l  the required cooling power is not delivered.
t  The air conditioner compressor is defective.
–  Rinse (clean) refrigerant circuit → Chapter.
–  Renew the air conditioner compressor and receiver.

   
Possible deviation from specificationPossible cause of faultRectifying fault
l  High pressure normal,
l  Low pressure is too low (see diagram),
l  the cooling power called for is delivered.
t  Expansion valve or air conditioner compressor defective.
–  Renew expansion valve.
–  Recharge refrigerant circuit.
–  Repeat check.

  Note!
t  If repeated test results in air conditioning system still not operating correctly, flush (clean) the refrigerant circuit → Chapter. Then renew the air conditioner compressor and receiver.
t  In this case, the evaporator may ice up although the correct quantity of refrigerant is present in the refrigerant circuit.
   
Possible deviation from specification Possible cause of faultRectifying fault
l  High pressure and low pressure are normal,
l  the required cooling power is not delivered.
Too much refrigerant in the circuit.
–  Evacuate refrigerant circuit.
–  Rinse (clean) refrigerant circuit → Chapter.
l  High pressure and low pressure are normal,
l  The air conditioner compressor is noisy (especially immediately after being switched on),
l  the cooling power called for is delivered.
  

  Note!
Overfilling with refrigerant oil can occur if the refrigerant oil level was not checked after the air conditioner compressor was renewed.
   

Working with the A/C service station > < Checking pressures on vehicles