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Audi A3 Workshop Service & Auto Repair Manuals | Mk1

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Checking pressures on vehicles with restrictor, reservoir and air conditioner compressor regulating valveN280 (with externally r > < Checking pressures on vehicles with an expansion valve and receiver (with internally regulated air conditioner compressor)

Refrigerant Pressure Specs: A3 Mk1, R134a, Expansion Valve, Regulated Compressor

Specifications for pressures in refrigerant circuit
Specifications for pressures in refrigerant circuit
High-pressure side:
Increasing from initial pressure (on connecting pressure gauges) up to max. 20 bar
Low-pressure side:
   
Decreasing from initial pressure (on connecting pressure gauges) to value in graph
A - High pressure in bar
B - Low pressure in bar
C - Permissible tolerance range
  A87-0146
Possible deviation from specification Possible causes of faultFault elimination
l  High pressure remains constant or only increases slightly (above pressure with engine stopped) 
l  Low pressure quickly drops to value in graph or below
l  Required cooling output is not attained
Not enough refrigerant in circuit or expansion valve defective
–  Extract refrigerant from refrigerant circuit.
l  If quantity of refrigerant extracted roughly corresponds to specified capacity:
–  Renew expansion valve.
–  Re-charge refrigerant circuit.
–  Repeat test.
l  High pressure normal
l  Low pressure in line with value in graph
l  Required cooling output is not attained
 
l  The quantity of refrigerant extracted is substantially less than the specified capacity.
–  Localise leak with leak detector and eliminate
–  Re-charge refrigerant circuit.
–  Repeat test.

  Note
If no fault can be found and air conditioner operation is not OK when the test is repeated, clean the refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter).
   
Possible deviation from specification Possible causes of faultFault elimination
l  High pressure does not increase or only to slightly above the pressure with the engine stopped,
l  low pressure does not decrease or only slightly.
l  Required cooling output is not attained
t  No actuation of the air conditioner compressor (magnetic clutch)
t  The air conditioner compressor is not driven.
–  Check actuation and drive of the air conditioner compressor and perform repair → Heating, air conditioning; Rep. gr.87 or → Air conditioning; Rep. gr.87
 
t  Constriction or blockage in the refrigerant circuit (e.g. in the refrigerant line between the „low-pressure end“ service connection and the air conditioner compressor).
–  Clean refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter).
–  Renew hose or pipe if kinked or constricted.
 
t  The air conditioner compressor is defective.
–  Renew air conditioner compressor.

   
Possible deviation from specification Possible causes of faultFault elimination
l  High pressure increases above specification
l  Low pressure quickly drops to value in graph or below
l  Required cooling output is not attained
t  Constriction or obstruction in refrigerant circuit
t  Expansion valve defective
–  Run hand over refrigerant circuit to check for differences in temperature
l  If difference in temperature is found at one component:
–  Renew hose or pipe if kinked or constricted.
–  In the event of clogging, clean the refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter and renew the expansion valve if applicable).
l  If no fault is found:
–  Clean the refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter and renew the expansion valve if applicable).
–  Repeat test.

  Note
If operation is not OK after cleaning the refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter), the expansion valve must be renewed.
   
Possible deviation from specification Possible causes of faultFault elimination
l  High and low pressure normal at first,
l  After some time, high pressure increases above specification and low pressure drops to value in graph or below
l  Required cooling output is no longer attained
t  Expansion valve defective
t  Moisture in refrigerant circuit
–  Renew receiver (with dryer) and evacuate refrigerant circuit for at least 3 hours (see notes)
–  Check expansion valve for dirt or corrosion and renew if necessary
–  Clean refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter).
l  High and low pressure normal at first
l  After lengthy operating period, low pressure drops excessively (evaporator ices up)
  

  Note
t  It is not initially necessary to clean the refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter) when this problem occurs. Normally, there is only a small quantity of moisture in the system which can be removed by lengthy evacuation.
t  If a problem involving moisture in the 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 renew the dryer (adjust the quantity of refrigerant oil). Subsequently, evacuate refrigerant circuit for at least 3 hours.
   
Possible deviation from specification Possible causes of faultFault elimination
l  High pressure normal or too high
l  Low pressure too high (see graph)
l  Required cooling output is not attained
l  The air conditioner compressor is noisy (especially immediately after being switched on).
t  Too much refrigerant in the circuit.
t  Expansion valve or air conditioner compressor defective.
–  Extract refrigerant from refrigerant circuit.
l  If quantity of refrigerant extracted roughly corresponds to specified capacity:
–  Renew expansion valve.
–  Re-charge refrigerant circuit.
–  Repeat test.
l  The quantity of refrigerant extracted is significantly greater than the prescribed charge quantity.
–  Re-charge refrigerant circuit.
–  Repeat test.

  Note
If operation of the air conditioning system is not OK when the test is repeated, re-fit the old expansion valve and clean the refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter). Then renew the air conditioner compressor and receiver.
   
Possible deviation from specificationPossible causes of faultFault elimination
l  High pressure only increases slightly above pressure with engine stopped
l  Low pressure only drops slightly
l  Required cooling output is not attained
The air conditioner compressor is defective.
–  Clean refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter).
–  Renew the air conditioner compressor and receiver.

   
Possible deviation from specification Possible causes of faultFault elimination
l  High pressure normal
l  Low pressure too low (see graph)
l  Required cooling output is attained
Expansion valve or air conditioner compressor defective.
–  Renew expansion valve.
–  Re-charge refrigerant circuit.
–  Repeat test.

  Note
t  If operation of the air conditioning system is not OK when the test is repeated, re-fit the old expansion valve and clean the refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → 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 causes of faultFault elimination
l  High and low pressure normal
l  Required cooling output is not attained
Too much refrigerant oil in the circuit.
–  Discharge refrigerant circuit.
–  Clean refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter).
l  High and low pressure normal
l  The air conditioner compressor is noisy (especially immediately after being switched on),
l  Required cooling output is attained
  

  Note
t  Overfilling with refrigerant oil may occur if, for example, the air conditioner compressor has been renewed without adjusting the quantity of refrigerant oil.
t  If there is too much refrigerant oil in the circuit, drain the air conditioner compressor and renew the receiver. After cleaning the refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter), add the correct amount of refrigerant oil to the circuit → Chapter.
   

Checking pressures on vehicles with restrictor, reservoir and air conditioner compressor regulating valveN280 (with externally r > < Checking pressures on vehicles with an expansion valve and receiver (with internally regulated air conditioner compressor)