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:

Decreasing from initial pressure (on connecting pressure gauges) to value in graph A -  Low pressure (measured at service connection) in bar absolute B -  Control current for air conditioner compressor regulating valve -N280- in amps C -  Permissible tolerance range (applicable to compressor capacity utilisation of 10...90 %).   Note t  In the event of a very high cooling output requirement (e.g. high ambient temperature and high fresh-air blower speed at low engine speed), the air conditioner compressor cannot initially set the pressure on the low-pressure end to the value -C- given in the graph (e.g. for a certain time after switching on the air conditioner). The air conditioner compressor is actuated with the maximum specified control current, however the delivery volume of the air conditioner compressor is no longer sufficient under these ambient conditions and at this engine speed to reduce the pressure on the low-pressure end to the value in the graph. One way of checking the control action of the air conditioner compressor under these conditions is to actuate the fresh-air blower with only approx. 40 % of the maximum voltage and to check the pressures at reduced fresh-air blower speed → Vehicle diagnostic tester („self-diagnosis“ or „Guided Fault Finding“ function for air conditioner) and → Heating, air conditioning; Rep. gr.87 or → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual). t  Under unfavourable conditions (very high ambient temperatures, high humidity), the pressure on the high-pressure end may increase up to max. 29 bar. t  The control current -B- is displayed in the measured value block of the operating and display unit for Climatronic air conditioning system -E87- or the Climatronic control unit -J255-. t  The high pressure measured by the high-pressure sender -G65- or the refrigerant pressure and temperature sender -G395- is displayed in the measured value block of the operating and display unit for Climatronic air conditioning system -E87- or the operating and display unit, Climatronic control unit -J255-. t  The low pressure settles as a function of the control current for the air conditioner compressor regulating valve -N280- and the control characteristic of the expansion valve within the air conditioner compressor output range in the tolerance band. t  Under unfavourable conditions (very high ambient temperatures, high humidity), the air conditioner compressor output may not always be sufficient to attain the specified value. t  If the compressor capacity utilisation is greater than 90 %, the pressure on the low-pressure end may be in excess of the tolerance range „C“ shown in the graph (the compressor output no longer suffices). t  The specified operating current for the air conditioner compressor regulating valve -N280- must be greater than 0.3 A to ensure reliable valve actuation. t  In the „maximum cooling output“ setting, the control current for the air conditioner compressor regulating valve -N280- is regulated to approx. 0.65 A (up to 0.85 A). This measured value is vehicle-specific and displayed in the measured value block. t  On the absolute pressure scale, 0 bar corresponds to an absolute vacuum. Normal ambient pressure corresponds to 1 bar absolute. On the scales of most pressure gauges, 0 bar corresponds to an absolute pressure of 1 bar (can be seen from -1 bar mark below 0) → Vehicle diagnostic tester („self-diagnosis“ or „Guided Fault Finding“ function for air conditioner) and → Heating, air conditioning; Rep. gr.87 or → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual).

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	t  Actuation of air conditioner compressor regulating valve -N280- not OK t  Not enough refrigerant in circuit t  Expansion valve defective	–  Check actuation of -N280- –  Extract refrigerant from refrigerant circuit. l  If quantity of refrigerant extracted is substantially less than specified capacity:
l  High pressure normal l  Low pressure in line with value in graph l  Required cooling output is not attained		–  Localise leak with leak detector and eliminate –  Re-charge refrigerant circuit. –  Repeat test.
l  High pressure normal l  Low pressure too low (see graph) l  Required cooling output is not attained		l  If quantity of refrigerant extracted roughly corresponds to specified capacity: –  Renew expansion valve. –  Re-charge refrigerant circuit. –  Repeat test.

t	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).

t	Check the measured values of the evaporator output temperature sender -G263- and actuation of -N280-. If the measured value of the evaporator output temperature sender -G263- is not OK, the evaporator may ice up or the cooling output is not attained.

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If, after renewing the expansion valve, operation of the air conditioning system is not OK when the test is repeated (re-fit old expansion valve), 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.

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If the expansion valve is defective (permanently closed or does not open sufficiently), -N280- is actuated to maximum output and the low pressure drops to the value in the graph or below (the air conditioner compressor draws off refrigerant from the low-pressure end). As however refrigerant cannot flow via the expansion valve, the cooling output is not attained and the high pressure may also not increase or only increase slightly due to the absence of energy conversion → Vehicle diagnostic tester („self-diagnosis“ or „Guided Fault Finding“ function for air conditioner) and → Heating, air conditioning; Rep. gr.87 or → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual).

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 (air conditioner compressor regulating valve -N280-) 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 pipe 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.

Note t  In the event of this problem, make sure the air conditioner compressor (air conditioner compressor shaft) is actually being driven via the pulley/drive unit → Heating, air conditioning; Rep. gr.87 / → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual). t  As of Model Year 2012, air conditioner compressors with both -N280- and an air conditioning system magnetic clutch -N25- fitted at the pulley are to be introduced for certain engines and models. In the event of this problem, make sure -N25- is actually being actuated and that the air conditioner compressor (air conditioner compressor shaft) is being driven via the pulley → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual) and → Electronic parts catalogue.

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 l  Required cooling output is not attained	t  Actuation of air conditioner compressor regulating valve -N280- not OK t  Constriction or obstruction in refrigerant circuit t  Expansion valve defective	–  Check actuation of -N280-. –  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). –  Re-charge refrigerant circuit. –  Repeat test. l  If no fault is found: –  Clean refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter). –  Re-charge refrigerant circuit. –  If function is not OK, repeat test: –  Renew expansion valve and receiver.

t	If the function of the air conditioning system is not OK when the test is repeated, renew expansion valve and receiver.

t	With this fault, the evaporator may ice up although the quantity of refrigerant in the circuit is OK.

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If the expansion valve is defective (permanently closed or does not open sufficiently), the air conditioner compressor regulating valve -N280- is actuated to maximum output and the low pressure drops to the value in the graph or below (the air conditioner compressor draws off refrigerant from the low-pressure end). As however refrigerant cannot flow via the expansion valve, the cooling output is not attained and the high pressure may also not increase or only increase slightly due to the absence of energy conversion → Vehicle diagnostic tester („self-diagnosis“ or „Guided Fault Finding“ function for air conditioner) and → Heating, air conditioning; Rep. gr.87 or → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual).

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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.

Possible deviation from specification	Possible causes of fault	Fault elimination
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	t  Actuation of air conditioner compressor regulating valve -N280- not OK t  Moisture in refrigerant circuit	–  Check actuation of -N280-. –  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 driving time, low pressure drops below specification (evaporator ices up)		–  Renew receiver with dryer. –  Evacuate refrigerant circuit for at least 3 hours. –  Re-charge refrigerant circuit. –  Repeat test.

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.

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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 in the receiver (adjust quantity of refrigerant oil). Subsequently, evacuate refrigerant circuit for at least 3 hours.

t	In this case, the evaporator may ice up although the correct quantity of refrigerant is present in the refrigerant circuit.

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A problem with evaporator output temperature sender -G263- can also cause icing-up of refrigerant circuit. If this problem is encountered, also pay attention to the measured value of the evaporator output temperature sender -G263- → Vehicle diagnostic tester („self-diagnosis“ or „Guided Fault Finding“ function for air conditioner) and → Heating, air conditioning; Rep. gr.87 or → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual).

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	t  Actuation of air conditioner compressor regulating valve -N280- not OK t  Expansion valve or air conditioner compressor defective. t  The air conditioner compressor is defective.	–  Check actuation of -N280-. –  Clean refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter) (not always necessary, refer to notes). –  Renew expansion valve and receiver. –  Re-charge refrigerant circuit. –  If function is not OK, repeat test: –  Renew air conditioner compressor. –  Re-charge refrigerant circuit. –  Repeat test.

t	Observe the following regarding fault „High pressure normal, low pressure too low“: This fault may cause the evaporator to ice up although the amount of refrigerant in the circuit is OK.

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If the problem is with -N280- (the regulating valve is not actuated but the air conditioner compressor operates nevertheless), the refrigerant circuit does not have to be cleaned (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter). It is sufficient in this case to renew the air conditioner compressor (heed quantity of refrigerant oil in air conditioner compressor).

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If the expansion valve is defective (permanently closed or does not open sufficiently), -N280- is actuated to maximum output and the low pressure drops to the value in the graph or below (the air conditioner compressor draws off refrigerant from the low-pressure end). As refrigerant cannot however flow via the expansion valve, the cooling output is not attained and the high pressure may either not increase or only slightly due to the absence of energy conversion.

t

Check the measured values of the evaporator output temperature sender -G263- and actuation of -N280-. If the measured value of the evaporator output temperature sender -G263- is incorrect, the evaporator may ice up or the cooling output is not attained → Vehicle diagnostic tester („self-diagnosis“ or „Guided Fault Finding“ function for air conditioner) and → Heating, air conditioning; Rep. gr.87 or → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual).

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  The air conditioner compressor is noisy (especially immediately after being switched on), l  Required cooling output is attained	t  Actuation of air conditioner compressor regulating valve -N280- not OK t  Too much refrigerant in the circuit. t  Expansion valve defective t  The air conditioner compressor is defective.	–  Check actuation of -N280-. –  Extract refrigerant from refrigerant circuit. l  The quantity of refrigerant extracted roughly corresponds to the actual capacity. –  Renew expansion valve and receiver. –  Re-charge refrigerant circuit. –  If function is not OK, repeat test: –  Renew the air conditioning system compressor. l  If quantity of refrigerant extracted is substantially greater than specified capacity: –  Re-charge refrigerant circuit. –  Repeat test.

t	This fault may also be caused by too much refrigerant oil in the circuit. 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 the expansion valve is defective (permanently closed or does not open sufficiently), -N280- is actuated to maximum output and the low pressure drops to the value in the graph or below (the air conditioner compressor draws off refrigerant from the low-pressure end). As however refrigerant cannot flow via the expansion valve, the cooling output is not attained and the high pressure may also not increase or only increase slightly due to the absence of energy conversion → Vehicle diagnostic tester („self-diagnosis“ or „Guided Fault Finding“ function for air conditioner) and → Heating, air conditioning; Rep. gr.87 or → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual).

Possible deviation from specification	Possible causes of fault	Fault elimination
l  High and low pressure normal l  Required cooling output is attained	t  Actuation of air conditioner compressor regulating valve -N280- not OK t  Too much refrigerant in the circuit. t  Expansion valve defective	–  Check actuation of -N280-. –  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		–  Add the correct quantity of refrigerant oil to the circuit (refer to note). –  Re-charge refrigerant circuit. –  If function is not OK, repeat test: –  Renew expansion valve. –  Re-charge refrigerant circuit. –  Repeat test.

t	Overfilling with refrigerant oil may occur if, for example, the air conditioner compressor has been renewed without adjusting the quantity of refrigerant oil.

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If the expansion valve is defective (permanently open), the evaporator temperature is no longer regulated such that only refrigerant in gas form exits from the evaporator. Under certain usage conditions, liquid droplets may then be drawn in by the air conditioner compressor and cause noise (liquid cannot be compressed).

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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.