Audi Workshop Service and Repair Manuals

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 (measured at service connection) in bar B -  Low pressure (measured at connection with valve at air conditioner compressor or reservoir) in bar C -  Permissible tolerance range D -  Low pressure (measured at connection with valve for low-pressure switch or at service connection) in bar E -  Permissible tolerance range

Possible deviation from specification	Possible causes of fault	Fault 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	–  Localise leak with leak detector and eliminate –  Re-charge refrigerant circuit.
l  High pressure normal l  Low pressure in line with value in graph l  Required cooling output is not attained
l  High pressure normal l  Low pressure too low (see graph) l  Required cooling output is not attained

If no fault is found for this problem, clean refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter).

Possible deviation from specification	Possible causes of fault	Fault 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  Air conditioner compressor defective.	–  Renew air conditioner compressor.

Possible deviation from specification	Possible causes of fault	Fault 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	Constriction or obstruction in refrigerant circuit	–  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 refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter). l  If no fault is found: –  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 some time, high pressure increases above specification and l  low pressure drops to value in graph or below, l  Required cooling output is no longer attained	Moisture in refrigerant circuit	–  Check and if necessary renew reservoir (with dryer) and restrictor, then evacuate refrigerant circuit for min. 3 hours (see note) –  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).

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.

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.

Possible deviation from specification	Possible causes of fault	Fault elimination
l  High pressure normal l  Low pressure too low (see graph) l  Required cooling output is 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 air conditioner compressor.

t	Observe the following regarding fault „High pressure normal, low pressure too low“: This fault may cause the evaporator to ice up or the low-pressure switch -F73- to shut off the air conditioner compressor although the amount of refrigerant in the circuit is OK.

t	On the Audi 100, Audi A6 (up to and including Model Year 1997) and the Audi V8, this fault may result in the air conditioner compressor being shut off by the operating and display unit (if the temperature at the fresh-air blower drops below -3 °C) → Heating, air conditioning; Rep. gr.87.

Possible deviation from specification	Possible causes of fault	Fault elimination
l  High pressure normal or too high l  Low pressure too high (see graph) l  air conditioner compressor noise (particularly after switch-on), l  Required cooling output is not attained	Too much refrigerant in the circuit.	–  Extract refrigerant from refrigerant circuit. l  If quantity of refrigerant extracted roughly corresponds to specified capacity: –  Renew the air conditioning system compressor. l  The quantity of refrigerant extracted is substantially greater than the specified capacity. –  Re-charge refrigerant circuit. –  Repeat test.

Possible deviation from specification	Possible causes of fault	Fault 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

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 reservoir. 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.