Specified Values For Refrigerant Circuit Pressures, Vehicles Without Heat Pump

On vehicles with a high-voltage system but without a heat pump (for example on Audi A3 e-tron, Audi Q5 hybrid, Audi A6 hybrid and Audi A8 hybrid) no check valves are installed in the refrigerant circuit. On these vehicles valves are installed in the refrigerant circuit which regulate the flow of the refrigerant to the evaporator (in the heater and A/C unit) or to the heat exchanger for the cooling of the components of the high-voltage system. These valves only have two operating conditions (open or closed). Refer to Refrigerant Circuit and use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  Function for A/C System and the Battery Regulation.

The temperature of the air after the evaporator, the current A/C compressor speed and the pressure of the refrigerant on the high pressure side are displayed depending on the vehicle as the measured value from the different control modules (for example the display control head, the Climatronic Control Module -J255-, the Front A/C Display Control Head -E87-, the Thermal Management Control Module -J1024- etc.). Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding"  function of the A/C system and the appropriate Wiring Diagram.

If a high cooling output is required (for example, a high outside temperature and the blower speed set on high), then the A/C compressor will not bring the pressure on the low pressure side to the required value (for example, for a certain time after turning on the A/C). The A/C compressor is not actuated at the maximum specified speed (of approximately 8500/min) on a stationary or slow moving vehicle (up to a speed of approximately 45km/h) (the A/C compressor speed is limited to approximately 5000/min). After a vehicle reaches a speed of more than approximately 45 km/h (28 mph), the limit for the maximum permissible A/C compressor speed is lifted. At a A/C compressor speed of 5000/min, a high outside temperature and a high fresh air blower speed (inefficient environmental controls), the A/C compressor output (the delivery volume) is no longer sufficient to reduce the pressure on the low pressure side to the target value. To check the A/C compressor control under these conditions, for example, the fresh air blower is controlled only with approximately 40% of the maximum voltage, check the pressures at a lower fresh air blower speed. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  Function for A/C System and the Battery Regulation and the COOLING OUTPUT, CHECKING .

Under unfavorable conditions (very high ambient temperatures, high humidity), pressure on high-pressure side may increase to max. 29 bar (421 psi).

The specified RPM of the A/C compressor is displayed as the measured value of the different control modules depending on the vehicle (for example from the display control head, the Climatronic Control Module -J255-). Refer to the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function of the A/C system and the appropriate Wiring Diagram.)

The measured high pressure of the respective sensor (for example from the A/C Pressure/Temperature Sensor -G395- or by the Refrigerant Circuit Pressure Sensor -G805-) is displayed as a measured value from the respective control module (for example from the Climatronic Control Module -J255- display control head). Use the Vehicle Diagnostic Tester "Guided Fault Finding"  function for the air conditioner and COOLING OUTPUT, CHECKING .

Depending on the A/C compressor speed and the control characteristic of the expansion valve, the low pressure settles within the A/C compressor output range in the tolerance range (1.5 to 2.3 bar (22 to 33 psi) positive pressure).

The target speed for the A/C compressor must be greater than 1500/min for this test.

In setting "maximum cooling output" the target speed is regulated to approximately 4000 up to 5000/min. This value is vehicle-specific and is displayed as a measured value of the respective control module (for example the Climatronic Control Module -J255-) display and control head. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  Function for A/C System and Battery Regulator.

At absolute pressure, 0 bar (0 psi) corresponds to absolute vacuum. Normal ambient pressure corresponds to 1 bar (14.5 psi) absolute pressure. On the scales of most pressure gauges, 0 bar corresponds to an absolute pressure of 1 bar (14.5 psi) (can be seen from -1 bar (-14.5 psi) mark below 0 bar (0 psi)). Use the Vehicle Diagnostic Tester in the function "Guided Fault Finding"  for the A/C System) and COOLING OUTPUT, CHECKING .

If, on a vehicle with two evaporators (for example on a Audi A8 hybrid, one in the A/C unit and one for cooling the high-voltage components, for example, in the battery cooling module or the high-voltage battery heat exchanger as in the Audi A3 e-tron), the measured temperature on one evaporator corresponds to the specified value or the specified value falls short, but does not reach the required specified value on the other evaporator, the following adjustment is performed: the responsible control module (the Battery Regulation Control Module -J840- or the Climatronic Control Module -J255-) activates the Electrical A/C Compressor -V470- with increased speed via various other control modules (for example, the Electric Drive Power and Control Electronics -JX1- and the A/C Compressor Control Module -J842-). Thereby increasing the A/C cooling output and decreasing the pressure on the low pressure side as well as the evaporator temperature. If the specified value for the temperature falls short at one evaporator, the relevant control module (for example the Battery Regulation Control Module -J840- or the Climatronic Control Module -J255-) activates the installed shut-off valves (Hybrid Battery Refrigerant Shut-Off Valve 1 -N516-, Heater and A/C Unit Refrigerant Shut-Off Valve -N541-, Hybrid Battery Refrigerant Shut-Off Valve 2 -N517- or High-Voltage Battery Heater Core Refrigerant Shut-Off Valve -N542-) so that the evaporator which is too cold is no longer supplied with refrigerant. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding " Function for the A/C System. Refer to the appropriate Wiring Diagram and COOLING OUTPUT, CHECKING .

Since the evaporator for cooling the high-voltage components output (in the battery cooling module and in the high-voltage battery heat exchanger) is essential for the evaporator output in the A/C unit, the required target temperature may still be reached in the evaporator for cooling the high-voltage battery with too little refrigerant in the refrigerant circuit, but the target temperature in the A/C unit evaporator will no longer be attainable (even though the A/C compressor is activated with increased A/C unit speed).

Read the supporting information. Refer to SPECIFIED VALUES FOR REFRIGERANT CIRCUIT PRESSURES, VEHICLES WITHOUT HEAT PUMP .

If no error is detected with this complaint, clean the refrigerant circuit (by flushing with refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or clean using compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN ). One of these malfunctions may arise due to a constriction or a blockage in the refrigerant circuit.

Depending on the vehicle, check the sensor measured values for the Evaporator Vent Temperature Sensor -G263- and, if equipped, the Temperature Sensor before Hybrid Battery Evaporator -G756- and the Temperature Sensor after Hybrid Battery Evaporator -G757- as well as the A/C compressor activation via the respective control modules (for example, the A/C Compressor Control Module -J842- by the Battery Regulation Control Module -J840- or the Climatronic Control Module -J255- A/C control head. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  Function for the A/C System, the A/C Compressor and the Battery Regulation and refer to Refrigerant Circuit and the appropriate Wiring Diagram.

If there is an error in the measured value for the Evaporator Vent Temperature Sensor -G263- (or, for example, the Temperature Sensor before Hybrid Battery Evaporator -G756- or the Temperature Sensor after Hybrid Battery Evaporator -G757-, depending on the vehicle), this can lead to problems in the cooling output or the evaporator in the A/C unit can ice over. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  Function for the A/C System, the A/C Compressor and the Battery Regulation and refer to Refrigerant Circuit .

If the A/C system function is not OK after repeating the test, for example after replacing expansion valve (reinstalling the old expansion valve), clean the refrigerant circuit by flushing using the refrigerant R134a or blowing through using the compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A and REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN . Then replace the A/C compressor and receiver/dryer or dryer cartridge.

With a malfunction on one of the temperature sensors, the evaporator may ice up even though the quantity of refrigerant in the circuit is OK.

If the expansion valve on the evaporator in the A/C unit (or for example the Hybrid Battery Refrigerant Shut-Off Valve 1 -N516- /Heater and A/C Unit Refrigerant Shut-Off Valve -N541-, depending on the vehicle) is faulty (constantly closed or does not open far enough), the A/C compressor is actuated to maximum output and the low pressure drops to the value in the graph or below (A/C compressor draws off refrigerant from the low pressure side). Since the refrigerant cannot flow via the expansion valve, the cooling output is not attained. High pressure may also not increase or only increase slightly due to the absence of energy. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  Function for the A/C System, the A/C Compressor and the Battery Regulation and refer to Refrigerant Circuit and COOLING OUTPUT, CHECKING .

The evaporator in the A/C system has more output than the evaporator for cooling the high-voltage components (depending on the vehicle for example in the battery cooling module or in the high-voltage battery heat exchanger). The shut-off valve (for example, the Hybrid Battery Refrigerant Shut-Off Valve 2 -N517- on the expansion valve in the battery cooling module or the High-Voltage Battery Heater Core Refrigerant Shut-Off Valve -N542-, depending on the vehicle) is currently activated only from or up to a certain battery temperature by the Battery Regulation Control Module -J840- or the Climatronic Control Module -J255- A/C control head (depending on the cooling design for the Electric Vehicle Battery -A2- /Hybrid Battery Unit -AX1- (hybrid battery), so that the energy exchange via the evaporator for cooling the high-voltage components (in the battery cooling module or in the high-voltage battery heat exchanger) only marginally increases or not at all. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  Function for the A/C System, the A/C Compressor and the Battery Regulation and refer to Refrigerant Circuit and COOLING OUTPUT, CHECKING .

On a vehicle with a battery cooling module, to cool the Electric Vehicle Battery -A2- (hybrid battery), for example the Hybrid Battery Refrigerant Shut-Off Valve 2 -N517- is currently activated by the Battery Regulation Control Module -J840- after a specific battery temperature is reached. If the A/C system driver is not already activated at this time, the Electrical A/C Compressor -V470- is activated via the A/C Compressor Control Module -J842- by the Battery Regulation Control Module -J840-. The temperature of the air in front of and behind the evaporator in the battery cooling module is determined by the Battery Regulation Control Module -J840-. If it can be determined that there is insufficient cooling, the information is stored in the Battery Regulation Control Module -J840-. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  Function for the A/C System, the A/C Compressor and the Battery Regulation and refer to Refrigerant Circuit .

On a vehicle with a battery cooling module, the temperature of the air (as well as the evaporator cooling output) in the battery cooling module is determined via the installed temperature sensor (it currently cannot be measured using a thermometer while operating) and may only be checked using the Guided Fault Finding. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding"  Function for the A/C System, the A/C Compressor and the Battery Regulation.

On a vehicle with a battery cooling module pay attention to the additional notes SPECIFIED VALUES FOR REFRIGERANT CIRCUIT PRESSURES, VEHICLES WITHOUT HEAT PUMP .

On a vehicle with a high-voltage battery heat exchanger depending on the vehicle (for example on an Audi A3 e-tron, on other vehicles the name of the components can vary) for cooling the high-voltage battery (for example the Electric Vehicle Battery -A2-, the High-Voltage Battery Charger Control Module -J1050- etc.) the High-Voltage Battery Heater Core Refrigerant Shut-Off Valve -N542- from a specified temperature of the control head, the Climatronic Control Module -J255- is no longer activated (the High-Voltage Battery Heater Core Refrigerant Shut-Off Valve -N542- is open without power). If the A/C system driver is not already activated at this time, the Electrical A/C Compressor -V470- is activated via the A/C Compressor Control Module -J842- from the Climatronic Control Module -J255- control head. So that the high-voltage battery is actually cooled by the coolant, additionally further components of the circuit must be activated (for example the Engine Coolant Circulation Pump 2 -V178- and the Solenoid Valve 1 -N88-) and coolant must be flowing through the high-voltage battery heat exchanger. If it can be determined that there is insufficient cooling to the high-voltage components, this information will be stored in various control modules. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  Function for the A/C System, the A/C Compressor and the Battery Regulation and refer to Refrigerant Circuit and CONNECTION DIAGRAM - COOLANT HOSES .

If no error is detected with this complaint, clean the refrigerant circuit (by flushing with refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or clean using compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN ). One of these malfunctions may arise due to a constriction or a blockage in the refrigerant circuit.

If the A/C system function is not OK when the test is repeated, replace the expansion valve and receiver/dryer (and the Hybrid Battery Refrigerant Shut-Off Valve 1 -N516- /Heater and A/C Unit Refrigerant Shut-Off Valve -N541-, if equipped). Refer to Refrigerant Circuit .

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

If the expansion valve on the evaporator in the A/C unit or the shut-off valve (for example, the Hybrid Battery Refrigerant Shut-Off Valve 1 -N516- or Heater and A/C Unit Refrigerant Shut-Off Valve -N541-) is faulty (constantly closed or does not open far enough), the A/C compressor is actuated to maximum output and the low pressure drops to the specified value or below (A/C compressor draws off refrigerant from the low pressure side). Since no (or little) refrigerant can flow via the expansion valve (or the corresponding shut-off valve), the cooling output is not attained. The high pressure may not increase or only increase slightly due to the absence of energy. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  Function for the A/C System, the A/C Compressor and the Battery Regulation and refer to Refrigerant Circuit and COOLING OUTPUT, CHECKING .

If, in a vehicle with a battery cooling module, the expansion valve on the evaporator in the battery cooling module is faulty (or if the function or activation of the Hybrid Battery Refrigerant Shut-Off Valve 2 -N517- is malfunctioning), constantly closed or does not open enough, then the A/C compressor is also activated with the maximum output (the required temperatures in the battery cooling module are not attained). The pressure on the low pressure side only falls to the specified value or lower when there is no cooling output requested at the same time in the A/C unit (the shut-off valve in front of the evaporator in the A/C unit for example the Hybrid Battery Refrigerant Shut-Off Valve 1 -N516- is activated and is closed). The A/C compressor extracts the refrigerant from the low pressure side from both evaporators). Since, however, no refrigerant can flow over the expansion valve in the A/C unit (for example the -Hybrid Battery Refrigerant Shut-Off Valve 1 N516-) and the cooling output in the battery cooling module is not attained (there is a malfunction in the battery cooling module), the electrical A/C compressor will be activated with a higher speed. Since, however, none of the refrigerant can flow through, the pressure on the low pressure side falls below the target value. In addition, the high pressure may not or only slightly increase, due to the absence of energy. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  Function for the A/C System, the A/C Compressor and the Battery Regulation and refer to Refrigerant Circuit and COOLING OUTPUT, CHECKING .

If, on a vehicle with a high-voltage battery heat exchanger, the restrictor installed in the refrigerant line to the high-voltage battery heat exchanger is plugged or the shut-off valve (for example the High-Voltage Battery Heater Core Refrigerant Shut-Off Valve -N542- on the Audi A3 e-tron) installed in this line is faulty, constantly closed or does not open wide enough, then the A/C compressor is also activated with the maximum output (the required temperatures in the battery cooling module are not attained). The pressure on the low pressure side only falls to the specified value or lower when there is no cooling output requested at the same time in the A/C unit (the Heater and A/C Unit Refrigerant Shut-Off Valve -N541- is activated and is closed on the Audi A3 e-tron, for example). The A/C compressor extracts the refrigerant from the low pressure side from both evaporators). Since, however, no refrigerant can flow via the expansion valve in the A/C unit (via the shut-off valve, for example the Heater and A/C Unit Refrigerant Shut-Off Valve -N541-) and the cooling output in the high-voltage battery heat exchanger is not attained, the electrical A/C compressor is activated with a higher speed. Since, however, none of the refrigerant can flow through, the pressure on the low pressure side falls below the target value. In addition, the high pressure may not or only slightly increase, due to the absence of energy. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  Function for the A/C System, the A/C Compressor and the Battery Regulation and refer to Refrigerant Circuit and COOLING OUTPUT, CHECKING . The same also applies when a malfunction occurs in the coolant circuit in which the high-voltage battery heat exchanger is installed (for example the Engine Coolant Circulation Pump 2 -V178- or the Solenoid Valve 1 - N88- on the Audi A3 e-tron are not correctly activated or are faulty). The high-voltage battery heat exchanger is then cooled, but the cooled coolant does not reach the high-voltage components. Refer to Coolant Circuit and CONNECTION DIAGRAM - COOLANT HOSES .

Since the evaporator output for cooling the high-voltage components output is smaller than the evaporator output in the A/C unit, the required specified temperature may still be reached in the evaporator for cooling the high-voltage battery with too little refrigerant in the circuit, but the specified temperature in the A/C unit evaporator will no longer be attainable (even though the A/C compressor is activated with increased speed).

If there is too much refrigerant oil in the circuit, the compressor must be drained (flushed) and the receiver/dryer or dryer cartridge must be replaced. After cleaning the refrigerant circuit by flushing with refrigerant R134a or blowing through using compressed air and nitrogen, then fill the circuit with the correct quantity of refrigerant oil (in the A/C compressor). Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A , REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN and REFRIGERANT R134A CAPACITIES, REFRIGERANT OIL AND APPROVED REFRIGERANT OILS .

It is not initially necessary to clean the refrigerant circuit by flushing using refrigerant R134a or blow through using compressed air and nitrogen when this problem occurs since normally, there is only a small quantity of moisture in the system which can be removed by lengthy evacuation. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A and REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN .

If a problem involving moisture in 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 replace the dryer installed in receiver/dryer (adjust quantity of refrigerant oil). Refrigerant circuit is then to be evacuated for at least three hours.

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

Likewise, the refrigerant circuit may become iced if there is a malfunction on the Evaporator Vent Temperature Sensor -G263- or/and on the Temperature Sensor after Hybrid Battery Evaporator -G757- (depending on the vehicle). For this complaint, also pay attention to the measured value of the Evaporator Vent Temperature Sensor -G263- and the Temperature Sensor after Hybrid Battery Evaporator -G757- (on vehicles with a battery cooling module, for example). Vehicle Diagnostic Tester in the "Guided Fault Finding"  function for the A/C system, and refer to Refrigerant Circuit and COOLING OUTPUT, CHECKING .

For the malfunction "high pressure normal, low pressure too low", note the following: With this fault, it may be that the evaporator in the A/C unit is icing up although the refrigerant quantity in the circuit is OK.

If there is a fault in the A/C compressor (the A/C compressor is activated by the A/C Compressor Control Module -J842- at too high of a speed), it is not necessary to clean the refrigerant circuit by flushing with refrigerant R134a or blowing through it with compressed air and nitrogen. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A or REFRIGERANT CIRCUIT, FLUSHING WITH COMPRESSED AIR AND NITROGEN . In this case, it is sufficient to replace the A/C compressor (observe quantity of refrigerant oil in A/C compressor and if necessary adjust).

If, on a vehicle with a battery cooling module, the expansion valve for the A/C unit evaporator or the expansion valve for the evaporator in the battery cooling module is faulty (constantly closed or does not far enough), the A/C compressor is also actuated to maximum output and the pressure on the low pressure side drops to value in graph or below (A/C compressor draws off refrigerant from low-pressure side). Since the refrigerant cannot flow via the faulty expansion valve, the cooling output in the downstream evaporator is not attained and the high pressure may also not increase or only increase slightly due to the absence of energy. The A/C compressor may thereby be activated with a higher speed since the required cooling output is not attained in an evaporator. The same also applies if the function or activation of a shut-off valve (for example, the Hybrid Battery Refrigerant Shut-Off Valve 1 -N516- or the Hybrid Battery Refrigerant Shut-Off Valve 2 -N517-, depending on the vehicle) is faulty. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function for the A/C system, and refer to Refrigerant Circuit and COOLING OUTPUT, CHECKING .

If, on a vehicle with a high-voltage battery heat exchanger, the expansion valve for the evaporator in the A/C unit is faulty (constantly closed or does not open far enough), or the restrictor in the refrigerant line to the high-voltage battery heat exchanger is plugged, the A/C compressor is also actuated to maximum output and the pressure on the low pressure side drops to value in graph or below (A/C compressor draws off refrigerant from the low-pressure side). Since the refrigerant cannot flow via the faulty expansion valve or the plugged restrictor, the cooling output in the downstream evaporator is not attained and the high pressure may also not increase or only increase slightly due to the absence of energy. The A/C compressor may thereby be activated with a higher speed since the required cooling output is not attained in an evaporator. The same also applies if the function or activation of a shut-off valve (for example, the Heater and A/C Unit Refrigerant Shut-Off Valve -N541-, or the High-Voltage Battery Heater Core Refrigerant Shut-Off Valve -N542-, depending on the vehicle) or one of the components installed in the coolant circuit for the high-voltage components (for example, the Engine Coolant Circulation Pump 2 -V178- or the Solenoid Valve 1 -N88- on the Audi A3 e-tron, depending on the vehicle) is faulty. Use the Vehicle Diagnostic Tester, and refer to CONNECTION DIAGRAM - COOLANT HOSES and Refrigerant Circuit .

Check the measured values of the Evaporator Vent Temperature Sensor -G263- (and if equipped the measured values of the Temperature Sensor Before Hybrid Battery Evaporator -G756- and the Temperature Sensor after Hybrid Battery Evaporator -G757-, depending on the vehicle) as well as the activation of the A/C compressor from the Battery Regulation Control Module -J840- or from the control head of the A/C system, the Climatronic Control Module -J255- or from the Front A/C Display Control Head -E87- or from the Thermal Management Control Module -J1024- (depending on the vehicle). If the measured value of the Evaporator Vent Temperature Sensor -G263- (the Temperature Sensor Before Hybrid Battery Evaporator -G756- or the Temperature Sensor after Hybrid Battery Evaporator -G757-, depending on the vehicle) or the activation of the A/C compressor faulty, the evaporator can freeze-up or the required cooling output is not reached. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function of the A/C system, and refer to Refrigerant Circuit and COOLING OUTPUT, CHECKING .

This fault may also be caused by too much refrigerant oil in the circuit. Overfilling with refrigerant oil can occur if, for example, the compressor has been replaced without adjusting the quantity of refrigerant oil.

If, on a vehicle with a battery cooling module, the expansion valve for the A/C unit evaporator or the expansion valve for the evaporator in the battery cooling module is faulty (constantly closed or does not far enough), the A/C compressor is also actuated to maximum output and the pressure on the low pressure side drops to value in graph or below (A/C compressor draws off refrigerant from low-pressure side). Since the refrigerant cannot flow via the faulty expansion valve, the cooling output in the downstream evaporator is not attained and the high pressure may also not increase or only increase slightly due to the absence of energy. The A/C compressor may thereby be activated with a higher speed since the required cooling output is not attained in an evaporator. The same also applies if the function or activation of a shut-off valve (for example, the Hybrid Battery Refrigerant Shut-Off Valve 1 -N516- or the Hybrid Battery Refrigerant Shut-Off Valve 2 -N517-, depending on the vehicle) is faulty. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function for the A/C system, and refer to Refrigerant Circuit .

If, on a vehicle with a high-voltage battery heat exchanger, the expansion valve for the evaporator in the A/C unit is faulty (constantly closed or does not open far enough), or the restrictor in the refrigerant line to the high-voltage battery heat exchanger is plugged, the A/C compressor is also actuated to maximum output and the pressure on the low pressure side drops to value in graph or below (A/C compressor draws off refrigerant from the low-pressure side). Since the refrigerant cannot flow via the faulty expansion valve or the plugged restrictor, the cooling output in the downstream evaporator is not attained and the high pressure may also not increase or only increase slightly due to the absence of energy. The A/C compressor may thereby be activated with a higher speed since the required cooling output is not attained in an evaporator. The same also applies if the function or activation of the Heater and A/C Unit Refrigerant Shut-Off Valve -N541-, the High-Voltage Battery Heater Core Refrigerant Shut-Off Valve -N542- (for example, on the Audi A3 e-tron) or one of the components installed in the coolant circuit for the high-voltage components (for example, the Engine Coolant Circulation Pump 2 -V178- or the Solenoid Valve 1 -N88- on the Audi A3 e-tron) is faulty. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function for the A/C system, and refer to CONNECTION DIAGRAM - COOLANT HOSES and Refrigerant Circuit .

Overfilling with refrigerant oil can occur if, for example, the compressor has been replaced without adjusting the quantity of refrigerant oil.

If, for example, the expansion valve in the evaporator in the A/C unit is faulty (permanently open), the evaporator temperature (in the A/C unit) is no longer regulated such that only refrigerant leaves the evaporator in a gaseous state. Under certain usage conditions, liquid droplets may then be drawn in by the compressor and cause noise (liquid cannot be compressed).

If there is too much refrigerant oil in the circuit, the compressor must be drained and the receiver/dryer must be replaced. After cleaning the refrigerant circuit by flushing with refrigerant R134a and fill the refrigerant circuit with the correct quantity of refrigerant. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A and REFRIGERANT R134A CAPACITIES, REFRIGERANT OIL AND APPROVED REFRIGERANT OILS .