Volkswagen Workshop Service and Repair Manuals

Specifications: High-pressure side: Rising from starting pressure (when pressure gauge is connected) to maximum 20 bar. Low-pressure side:

Falling from starting pressure (when pressure gauge is connected) to diagram value. A -  High pressure (measured at the service connection) in bar positive pressure. B -  Low pressure (measured at the connection with the valve at the air conditioner compressor or at the reservoir) in bar positive pressure. C -  Permitted tolerance range. D -  Low pressure (measured at the connection with the valve for the low-pressure switch or at the service connection) in bar positive pressure. E -  Permitted tolerance range.

Possible deviation from specification	Possible cause of fault	Rectifying 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 output is not delivered.	Insufficient refrigerant in circuit.	–  Look for leaks and rectify them. –  Recharge refrigerant circuit.
l  High pressure is normal, l  Low pressure matches the diagram value, l  The required cooling output is not delivered.
l  High pressure is normal, l  Low pressure is too low (see diagram), l  The required cooling output is not delivered.

If no fault can be found for this complaint, purge refrigerant circuit with refrigerant R134a → Chapter. If this is not possible in your workshop, blow through refrigerant circuit with compressed air and dry with nitrogen → Chapter.

Possible deviation from specification	Possible cause of fault	Rectifying 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 output is not delivered.	The air conditioner compressor is defective.	–  Purge (clean) refrigerant circuit → Chapter. –  Renew air conditioner compressor.

Possible deviation from specification	Possible cause of fault	Rectifying fault
l  High pressure rises above specification, l  Low pressure falls quickly to the diagram value or lower, l  The required cooling output is not delivered.	Restriction or obstruction in the refrigerant circuit.	–  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, blow through refrigerant circuit with compressed air and nitrogen. –  Repeat the check; if the system does not operate correctly –  Rinse (clean) refrigerant circuit → Chapter.
l  High pressure and low pressure are normal at first, but after a time, l  The high pressure increases beyond the specified value, l  The low pressure falls to the diagram value or lower, l  The cooling power called for is not delivered.	Moisture in the refrigerant circuit.	–  Blow through 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.
l  High pressure is normal, l  Low pressure is too low (see diagram), l  The cooling power required is delivered.	The air conditioner compressor is defective.	–  Rinse (clean) refrigerant circuit → Chapter. –  Renew air conditioner compressor.

t	If the fault is „high pressure normal, low pressure too low “ please note the following:

t	In this case, the evaporator may be iced up or the low-pressure switch for air conditioning system -F73- has switched off the air conditioning system compressor, although the correct quantity of refrigerant is present in the refrigerant circuit.

Possible deviation from specification	Possible cause of fault	Rectifying fault
l  High pressure normal or too high, l  Low pressure too high (see diagram), l  The air conditioner compressor is noisy (especially immediately after being switched on), l  The required cooling output is not delivered.	Too much refrigerant in circuit.	–  Extract some refrigerant from the refrigerant circuit. l  The quantity of refrigerant extracted is about equal to the prescribed charge quantity. –  Renew the air conditioner compressor. l  The quantity of refrigerant extracted is significantly greater than the prescribed charge quantity. –  Recharge refrigerant circuit. –  Repeat check.

Possible deviation from specification	Possible cause of fault	Rectifying fault
l  High-pressure and low-pressure are normal, l  The required cooling output is not delivered.	Too much refrigerant oil in circuit.	–  Drain 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 required is delivered.

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

t

If the air conditioner compressor is not to be replaced, drain refrigerant oil from air conditioner compressor via the drain plug. From the total amount of refrigerant oil, fill 50 g direct into air conditioner compressor and fill remainder in refrigerant circuit according to → vehicle-specific workshop manual.