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: Dropping from initial pressure (on connecting pressure gauges) to a value between 1.5 and 2.3 bar absolute (depending on cooling output required). Air conditioner compressor speed: Between 800 and 8600 rpm depending on cooling output required (currently max. 5000 rpm with vehicle stationary)   Note t  The temperature of the air downstream of the evaporator, the current air conditioner compressor speed and the refrigerant pressure on the high-pressure end are displayed as measured values by the operating and display unit, Climatronic control unit -J255- → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner t  In the event of a very high cooling output requirement (e.g. high ambient temperature and high fresh-air blower speed), the air conditioner compressor cannot initially set the pressure on the low-pressure end to the necessary value (e.g. for a certain time after switching on the air conditioner). When the vehicle is stationary or only moving slowly (up to a vehicle speed of approx. 45 km /h), the air conditioner compressor is not actuated at the maximum specified speed (of approx. 8500 rpm) (the air conditioner compressor speed is limited to approx. 5000 rpm). Limitation of the maximum permissible air conditioner compressor speed is only cancelled as of a vehicle speed of more then approx. 45 km/h. At an air conditioner compressor speed of 5000 rpm, with a high ambient temperature and a high fresh air blower speed (unfavourable ambient conditions), the output (delivery volume) of the air conditioner compressor is not sufficient at first to reduce the pressure on the low-pressure end to the specified value. 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, „Guided Fault Finding“ function for air conditioner and battery regulation and → 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 specified speed of the air conditioner compressor is displayed as measured value by the operating and display unit, Climatronic control unit -J255- → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner. t  The high pressure measured by the refrigerant pressure and temperature sender -G395- is displayed as measured value by the operating and display unit, Climatronic control unit -J255- → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner. t  Depending on the speed of the air conditioner compressor and the control characteristic of the expansion valve, the low pressure settles in the tolerance band within the air conditioner compressor output range (1.5 to 2.3 bar). t  The specified speed of the air conditioner compressor must be greater than 1500 rpm for this test. t  In the „maximum cooling output“ setting, the specified speed is regulated to approx. 4000 to 5000 rpm. This value is vehicle-specific and is displayed as measured value by the operating and display unit, Climatronic control unit -J255- → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner and battery regulation. 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, „Guided Fault Finding“ function for air conditioner and → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual). t  If, on a vehicle with two evaporators (one each in air conditioning unit and battery cooling module), the measured temperature corresponds to or is below the specified value at one evaporator but the required specified value is not attained at the other evaporator, the system is controlled as follows: The battery regulation control unit -J840- actuates the electric air conditioner compressor at a higher speed via the power and control electronics for electric drive -JX1- and the control unit for air conditioning compressor -J842-. This causes the cooling output of the air conditioner to increase and the pressure on the low-pressure side and the evaporator temperature to drop. If the temperature set value is then not reached at one evaporator, -J840- actuates the shut-off valve 1 for refrigerant of hybrid battery -N516- or the shut-off valve 2 for refrigerant of hybrid battery -N517- such that refrigerant no longer flows through the evaporator which is too cold → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner t  As the output of the evaporator in the battery cooling module is considerably less than that of the evaporator in the air conditioning unit, the specified temperature required may still be attained in the battery cooling module with insufficient refrigerant in the circuit, however the specified temperature will no longer be attained in the evaporator in the air conditioning unit (although the air conditioner compressor is being actuated at a higher speed).

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 specified value or below. l  the required cooling output is not attained in the evaporator in the air conditioning unit (and in the evaporator in the battery cooling module).	t  Actuation of air conditioner compressor not OK → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner, air conditioner compressor and battery regulation. t  Not enough refrigerant in circuit t  Expansion valve for evaporator in air conditioning unit defective. t  Refrigerant shut-off valve 1 for hybrid battery -N516- defective (blocked)	–  Check actuation and operation of the air conditioner compressor –  Extract refrigerant from refrigerant circuit. l  If quantity of refrigerant extracted is substantially less than specified capacity: –  Localise leak with leak detector and eliminate –  Re-charge refrigerant circuit. –  Repeat test.
l  High pressure normal l  low pressure corresponds to specified value, l  Required cooling output is not attained		l  If quantity of refrigerant extracted roughly corresponds to specified capacity: –  Check operation of refrigerant shut-off valve 1 for hybrid battery -N516- –  Renew expansion valve. –  Re-charge refrigerant circuit. –  Repeat test.

Observe notes → Anchor.

Possible deviation from specification	Possible causes of fault	Fault elimination
On vehicles without refrigerant shut-off valve 1 for hybrid battery -N516- l  High pressure normal l  low pressure too low (below specified value) l  Required cooling output is not attained at evaporator in air conditioning unit.	t  Actuation of air conditioner compressor not OK → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner, air conditioner compressor and battery regulation. t  Not enough refrigerant in circuit t  Expansion valve for evaporator in air conditioning unit defective.	–  Extract refrigerant from refrigerant circuit. l  If quantity of refrigerant extracted is substantially less than specified capacity: –  Localise leak with leak detector and eliminate –  Re-charge refrigerant circuit. –  Repeat test. l  If quantity of refrigerant extracted roughly corresponds to specified capacity: –  Renew expansion valve. –  Re-charge refrigerant circuit. –  Repeat test.
On vehicles with -N516- l  High pressure normal l  low pressure too low (below specified value) l  The required cooling output is not attained at the evaporator in the air conditioning unit and at the evaporator in the battery cooling module.	t  Actuation of air conditioner compressor not OK → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner, air conditioner compressor and battery regulation. t  Not enough refrigerant in circuit t  Expansion valve for evaporator in air conditioning unit defective. t  -N516- defective (blocked)	–  Extract refrigerant from refrigerant circuit. l  If quantity of refrigerant extracted is substantially less than specified capacity (continue as described for vehicles without -N516-) l  If quantity of refrigerant extracted roughly corresponds to specified capacity: –  Check actuation and operation of -N516- and -N517- –  Renew expansion valve. –  Re-charge refrigerant circuit. –  Repeat test.

t	If no fault is found for this problem, clean the refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter). Constriction or blockage in the refrigerant circuit may also lead to one of these problems

t

Check the measured values of the evaporator output temperature sender -G263- and, if fitted, of the temperature sensor upstream of evaporator for hybrid battery -G756- and of the temperature sensor downstream of evaporator for hybrid battery -G757- as well as actuation of the air conditioner compressor by way of the control unit for air conditioning compressor -J842- by the battery regulation control unit -J840- → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner and battery regulation.

t	An incorrect -G263-, -G756- or -G757- measured value may also cause problems with the cooling output or the evaporator may ice up.

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If, after renewing the expansion valve for example, operation of the air conditioner 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/dryer cartridge.

t	In the event of a fault at a temperature sensor, the evaporator may ice up although the quantity of refrigerant in the circuit is OK.

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If the expansion valve at the evaporator in the air conditioning unit or -N516- is defective (is permanently closed or does not open sufficiently), the air conditioner compressor is actuated to maximum output and the low pressure drops to the value in the graph or below (air conditioner compressor draws off refrigerant from low-pressure side). 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, „Guided Fault Finding“ function for air conditioner and battery regulation and → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual).

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The output of the evaporator in the air conditioning unit is considerably higher than that of the evaporator in the battery cooling module. Depending on the version, the refrigerant shut-off valve 2 for hybrid battery -N517- at the expansion valve in the battery cooling module is currently only actuated by the battery regulation control unit -J840- in order to cool the drive battery -A2- (hybrid battery) only when the battery reaches a certain temperature; energy conversion via the evaporator in the battery cooling module is not increased or only slightly increased → Vehicle diagnostic tester in „Guided Fault Finding“ mode for air conditioner and battery regulation and → Air conditioning; Rep. gr.87.

Possible deviation from specification	Possible causes of fault	Fault elimination
On vehicles with -N516- l  High pressure normal l  low pressure too low (below specified value) l  The required cooling output is not attained solely at the evaporator in the air conditioning unit (the cooling output is OK at the evaporator in the battery cooling module).	t  Actuation of air conditioner compressor not OK → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner, air conditioner compressor and battery regulation. t  Not enough refrigerant in circuit t  Expansion valve for evaporator in air conditioning unit defective. t  Refrigerant shut-off valve 1 for hybrid battery -N516- defective (blocked)	–  Extract refrigerant from refrigerant circuit. l  If 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. l  If quantity of refrigerant extracted roughly corresponds to specified capacity: –  Check actuation and operation of -N516-. Renew expansion valve at evaporator in air conditioning unit if no fault is found. –  Re-charge refrigerant circuit. –  Repeat test.
l  High pressure normal l  low pressure too low (below specified value) l  The required cooling output is not attained solely at the evaporator in the battery cooling module (the cooling output is OK at the evaporator in the air conditioning unit).	t  Actuation or operation of refrigerant shut-off valve 2 for hybrid battery -N517-, of a control motor, blower or temperature sensor in or at battery cooling module not OK. t  Constriction or blockage in the refrigerant line to or from the expansion valve at the battery cooling module t  Expansion valve for evaporator in battery cooling module defective. t  Not enough refrigerant in circuit	–  Check operation and actuation of the battery cooling module components → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner, air conditioner compressor and battery regulation –  Check refrigerant lines –  Extract refrigerant from refrigerant circuit. –  Renew expansion valve with -N517- –  Re-charge refrigerant circuit. –  Repeat test.

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The refrigerant shut-off valve 2 for hybrid battery -N517- is currently only actuated by the battery regulation control unit -J840- in order to cool the drive battery -A2- (hybrid battery) when the battery reaches a certain temperature. If air conditioning mode has not already been activated at this point, the electrical air conditioner compressor -V470- is actuated via the control unit for air conditioning compressor -J842- by -J840-. The temperature of the air upstream and downstream of the evaporator in the battery cooling module is determined by -J840-. If it is established that the cooling action is not sufficient, this is stored in -J840- → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner, air conditioner compressor and battery regulation

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The temperature of the air (and thus the cooling output of the evaporator) in the battery cooling module is determined by way of built-in temperature sensors (at present it cannot be measured with a thermometer during operation) and can only be checked using the Guided Fault Finding routine → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner, air conditioner compressor and battery regulation.

t	For further information, refer to → Anchor

Possible deviation from specification	Possible causes of fault	Fault elimination
On vehicles with refrigerant shut-off valve 1 for hybrid battery -N516- 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  the required cooling output is not attained in the evaporator in the air conditioning unit (and in the evaporator in the battery cooling module).	t  No actuation of air conditioner compressor, air conditioner compressor is not driven. t  -N516- defective (blocked)	–  Check actuation and operation of the air conditioner compressor and repair if necessary → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner and battery regulation –  Check actuation and operation of -N516-. Renew expansion valve at evaporator in air conditioning unit if no fault is found.
	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.

Possible deviation from specification	Possible causes of fault	Fault elimination
On vehicles without refrigerant shut-off valve 1 for hybrid battery -N516- l  High pressure increases above specification l  low pressure quickly drops to specified value, l  the required cooling output is not attained in the evaporator in the air conditioning unit (and in the evaporator in the battery cooling module).	t  Actuation or operation of air conditioner compressor not OK. t  Constriction or obstruction in refrigerant circuit t  Expansion valve defective	–  Check actuation and operation of the air conditioner compressor and repair if necessary → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner and battery regulation –  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 operation is not OK and 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.
On vehicles with -N516- l  High pressure increases above specification l  low pressure quickly drops to specified value, l  the required cooling output is not attained in the evaporator in the air conditioning unit (and in the evaporator in the battery cooling module).	t  Actuation or operation of air conditioner compressor or -N516- not OK t  Constriction or obstruction in refrigerant circuit t  Expansion valve defective	–  Check actuation of air conditioner compressor and -N516- → Vehicle diagnostic tester in „Guided Fault Finding“ mode for air conditioner and battery regulation. –  Further testing as described for vehicles without -N516-

t	If the operation of the air conditioner is not OK when the test is repeated, renew the expansion valve and receiver (and -N516- if fitted).

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 at the evaporator in the air conditioning unit or -N516- is defective (is permanently closed or does not open sufficiently), the air conditioner compressor is actuated to maximum output and the low pressure drops to the specified value or below (air conditioner compressor draws off refrigerant from low-pressure side). However, as refrigerant cannot flow via expansion valve -N516-, cooling output is not attained and high pressure may also not increase or only increase slightly since there is no energy conversion → Vehicle diagnostic tester in „Guided Fault Finding“ mode for air conditioner and battery regulation and → Air conditioning; Rep. gr.87 (vehicle-specific Workshop Manual).

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If the expansion valve at the evaporator in the battery cooling module is defective (or refrigerant shut-off valve 2 for hybrid battery -N517- is not operating or is not actuated properly), or if the expansion valve is permanently closed or does not open sufficiently, the air conditioner compressor is also actuated to maximum output (the required temperatures in the battery cooling module are not reached). The pressure on the low-pressure side then only drops to or below the specified value if no cooling output is requested in the air conditioning unit at the same time (-N516- is actuated and closed). The air conditioner compressor draws off the refrigerant from the low-pressure end of both evaporators). However, as no refrigerant can flow via the expansion valve in the air conditioning unit (-N516-) and the cooling output is not reached in the battery cooling module (fault in area of battery cooling module), the electric air conditioner compressor is actuated at a higher speed. As however no more refrigerant can flow, the pressure on the low-pressure end drops below the specified value and the high pressure may also not increase or only increase slightly due to the absence of energy conversion → Vehicle diagnostic tester, „Guided Fault Finding“ function for air conditioner and battery regulation and → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual).

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As the output of the evaporator in the battery cooling module is considerably less than that of the evaporator in the air conditioning unit, the specified temperature required may still be attained in the battery cooling module with insufficient refrigerant in the circuit, however the specified temperature will no longer be attained in the evaporator in the air conditioning unit (although the air conditioner compressor is being actuated at a higher speed).

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If there is too much refrigeration oil in the circuit, also drain (flush) the air conditioner compressor and renew the receiver/dryer cartridge. After cleaning the refrigerant circuit (flushing with refrigerant R134a → Chapter or blowing out with compressed air and nitrogen → Chapter), add the correct amount of refrigeration oil to the circuit (to the air conditioner compressor) → 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 specified value or below, l  the required cooling output is not attained in the evaporator in the air conditioning unit (and in the evaporator in the battery cooling module).	t  Actuation or operation of air conditioner compressor or -N516- not OK t  Moisture in refrigerant circuit	–  Check actuation of air conditioner compressor and -N516- → Vehicle diagnostic tester in „Guided Fault Finding“ mode for air conditioner and battery regulation. –  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 refrigeration oil). Subsequently, evacuate refrigerant circuit for at least 3 hours.

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

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A fault at the evaporator output temperature sender -G263- or / and if fitted at the temperature sensor downstream of evaporator for hybrid battery -G757- may also cause the refrigerant circuit to ice up. If this problem occurs, also heed the measured value for -G263- and -G757- (on vehicles with a battery cooling module) → Vehicle diagnostic tester and → 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 l  the required cooling output is not attained in the evaporator in the air conditioning unit (and in the evaporator in the battery cooling module).	t  Actuation or operation of air conditioner compressor or -N516-/-N517- (if installed) not OK t  Expansion valve in air conditioning unit or, if fitted, in battery cooling module defective. t  The air conditioner compressor is defective.	–  Check actuation and operation of air conditioner compressor and -N516-/-N517- (if installed) → Vehicle diagnostic tester in „Guided Fault Finding“ mode for air conditioner and battery regulation. –  Clean refrigerant circuit (flush with refrigerant R134a → Chapter or blow out with compressed air and nitrogen → Chapter) (not always necessary, refer to notes). –  Renew the expansion valve for the evaporator in the air conditioning unit (and for the evaporator in the battery cooling module) as well as the receiver / dryer. –  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 the air conditioner compressor (the air conditioner compressor is actuated at excessively high speed by the air conditioner compressor regulating valve -J842-), the refrigerant circuit does not have to be cleaned (flushed with refrigerant R134a → Chapter or blown 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 (or one of the two expansion valves) is defective (permanently closed or does not open sufficiently), the air conditioner compressor is also actuated to maximum output and the pressure on the low-pressure end 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 defective expansion valve, the cooling output is not attained in the downstream evaporator and the high pressure may either not increase or only increase slightly due to the absence of energy conversion. The air conditioner compressor may however be actuated at higher speed, as the required cooling output is not being attained in one evaporator. The same also applies if operation or actuation of the shut-off valve 1 for refrigerant of hybrid battery -N516- or shut-off valve 2 for refrigerant of hybrid battery -N517- is not OK → Vehicle diagnostic tester and → Heating, air conditioning; Rep. gr.87 or → Air conditioning; Rep. gr.87 (vehicle-specific workshop manual).

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Check the measured values for the evaporator output temperature sender -G263- (and if applicable the measured values for the temperature sensor upstream of evaporator for hybrid battery -G756- and the temperature sensor downstream of evaporator for hybrid battery -G757-) as well as actuation of the air conditioner compressor by the control unit for air conditioning compressor -J842-. If the measured value of -G263- (or -G756-, -G757-) or actuation of the air conditioner compressor is not OK, the evaporator may ice up or the required cooling output is not attained → Vehicle diagnostic tester 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, l  The air conditioner compressor is noisy (especially immediately after being switched on), l  the required cooling output is not attained in the evaporator in the air conditioning unit and/or in the evaporator in the battery cooling module.	t  Actuation or operation of air conditioner compressor not OK. t  Too much refrigerant in the circuit. t  Expansion valve defective t  The air conditioner compressor is defective.	–  Check actuation and operation of air conditioner compressor and -N516-/-N517- (if installed) → Vehicle diagnostic tester in „Guided Fault Finding“ mode for air conditioner and battery regulation. –  Extract refrigerant from refrigerant circuit. l  The quantity of refrigerant extracted roughly corresponds to the actual capacity. –  Renew the expansion valve for the evaporator in the air conditioning unit (and for the evaporator in the battery cooling module) as well as the receiver / dryer. –  Re-charge refrigerant circuit. –  Repeat the test, if operation is not OK: –  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.

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If the expansion valve for the evaporator in the air conditioning unit (or for the evaporator in the battery cooling module) is defective (permanently closed or does not open sufficiently), the air conditioner compressor is actuated to maximum output and the low pressure drops to the specified value 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 also either not increase or only increase slightly due to the absence of energy conversion. The same also applies if operation or actuation of the shut-off valve 1 for refrigerant of hybrid battery -N516- or shut-off valve 2 for refrigerant of hybrid battery -N517- is not OK → Vehicle diagnostic tester 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  the required cooling output is not attained in the evaporator in the air conditioning unit (and in the evaporator in the battery cooling module).	t  Actuation or operation of air conditioner compressor not OK. t  Actuation or operation of -N516-/-N517- not OK t  Too much refrigerant in the circuit. t  Expansion valve defective	–  Check actuation and operation of air conditioner compressor and -N516-/-N517- (if installed) → Vehicle diagnostic tester in „Guided Fault Finding“ mode for air conditioner and battery regulation. –  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  the required cooling output is not attained in the evaporator in the air conditioning unit (and in the evaporator in the battery cooling module).		–  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 for example the expansion valve is defective (permanently open), the evaporator temperature (in the air conditioning unit) 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).

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 (flushing with refrigerant R134a → Chapter), add the correct amount of refrigeration oil to the circuit → Chapter.