Specified Values For Refrigerant Circuit Pressures, Vehicles With Heat Pump

On vehicles with a high-voltage system and heat pump (for example on the Audi Q7 e-tron) installed in the refrigerant circuit and electrically activated vehicles which regulate the flow of the refrigerant in the refrigerant circuit depending on the current operating condition. There are different versions of these valves. Refer to Refrigerant Circuit and use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function.

For vehicles with the "heat pump" function and/or "high-voltage battery cooling", high pressure is not at the high pressure side service connection in every A/C system operating condition. Depending on the A/C system operating condition, the refrigerant circuit pressure on the high pressure side can only be measured via the pressure/temperature sensor installed in the refrigerant circuit on these vehicles. Refer to Refrigerant Circuit and use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function.

On these vehicles the refrigerant circuit of the A/C system is used not only to cool the vehicle interior but also to cool the Hybrid Battery Unit -AX1- (via the refrigerant circuit for the high-voltage system) and to heat the vehicle interior (at low ambient temperature) via the heat pump function. So in order for these functions to be performed, the various valves, pressure and temperature sensors as well as the pumps in the refrigerant circuit and in the high-voltage system coolant circuit must be installed correctly and function correctly. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function and refer to Refrigerant Circuit and COOLANT, DRAINING AND FILLING .

To determine the possible cause of a malfunction, the basic setting of the Thermal Management Control Module -J1024- different routines are stored, which activate these functions "Cooling the A/C system", "heat pump", and "Cooling the components of the high-voltage system" in the Vehicle Diagnostic Tester "Guided Fault Finding"  function.

Depending on the layout of the high pressure side service connection and the operating condition, the high pressure can only be measured via the pressure/temperature sensor installed in the refrigerant circuit. Refer to Refrigerant Circuit .

The temperature of the air downstream of the evaporator, the current A/C compressor speed and the pressure of the refrigerant on the high pressure side are displayed as the measured value by various control modules (for example, by the Thermal Management Control Module -J1024-, the Front A/C Display Control Head -E87- or the Climatronic Control Module -J255-), depending on the vehicle. Refer to Refrigerant Circuit and use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function.

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 activated 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 refer to COOLING OUTPUT, CHECKING .

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

The specified speed of the A/C compressor is displayed and the measured value for example from the Thermal Management Control Module -J1024- using the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function.

The refrigerant circuit pressure (low or high pressure) measured by the different pressure/temperature sensors depending on the respective operating condition is displayed as the measured value by the respective control module. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function and refer to Refrigerant Circuit .

The low pressure settles depending on the A/C compressor speed and the control characteristic of the expansion valve (on the evaporator of the front heater and A/C unit) within the compressor output range in tolerance range (1.5 to 2.3 bar 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 and the measured value of the respective control module using the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function.

At absolute pressure, 0 bar corresponds to absolute vacuum. Normal ambient pressure corresponds to 1 bar absolute pressure. 0 bar pressure corresponds to an absolute pressure of 1 bar on most pressure gauges (indicated by -1 bar below 0).

If on a vehicle with two evaporators (one in the heater and A/C unit and one for cooling the heater and A/C unit for example the heat exchanger for the high-voltage battery) and two condensers (one in the front end for the A/C system and one as the heat exchanger for the heat pump function) depending on the selected function on a component the measured temperature or pressure, the specified value corresponds to another component whose specifications are not achieved, check the activation of the electrically activated valves installed in the refrigerant circuit. At the same time, also pay attention to the pressure distribution in the refrigerant circuit depending on the installed check valves. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function and refer to Refrigerant Circuit .

For the correct A/C function it is also necessary that depending on the selected functions of the respective heater cores enough heat is supplied or removed. Therefore also pay attention to the incorporation of the heater core into the respective coolant circuit for the engine and high-voltage system and the function of the pumps and valves installed in it. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function and refer to Coolant Circuit .

Since the evaporator for cooling the high-voltage components output (in the battery cooling module and in the high-voltage battery heat exchanger) is smaller than the evaporator output in the heater and 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 heater and A/C unit evaporator will no longer be attainable (even though the A/C compressor is activated with increased A/C unit speed).

To determine the possible cause of a malfunction, the basic setting of the respective control module (for example in the Thermal Management Control Module -J1024-) different routines are stored, which activate these functions "Cooling the A/C system", "heat pump", and "Cooling the Thermal Management Control Module component of the high-voltage system" in the Vehicle Diagnostic Tester "Guided Fault Finding"  function.

If for this concern no malfunction can be determined, check the activation of the electrically activated valves installed in the refrigerant circuit next. If no error can be detected here, remove and check the check valves installed in the refrigerant circuit. If no error can be detected here either, clean the refrigerant circuit (flush with refrigerant R134a). A constriction or blockage in the refrigerant circuit can also lead to these complaints. Refer to Refrigerant Circuit and REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A .

For vehicles with the "heat pump" function and/or "high-voltage battery cooling", high pressure is not at the high pressure side service connection in every A/C system operating condition. Depending on the A/C system operating condition, the refrigerant circuit pressure on the high pressure side can only be measured via the pressure/temperature sensor installed in the refrigerant circuit on these vehicles. Refer to Refrigerant Circuit and use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function.

Before beginning the repair work check the measured values of the different pressure/temperature sensors installed in the refrigerant circuit. If there is an error in the measured value of a pressure/temperature sensor, this can lead to problems in the cooling output, or the evaporator in the front heater and A/C unit can ice over. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function. Refer to Refrigerant Circuit , and the appropriate Wiring Diagram.

When checking the different functions (heat pump or cooling the high-voltage battery), also pay attention to the activation and function of the coolant circuit components that are involved with these functions. Refer to Coolant 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. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A . 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 is faulty (constantly closed or does not open far enough), the A/C compressor is activated to maximum output and the low pressure drops to the value in the graph or below (A/C compressor draws off the 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 and COOLING OUTPUT, CHECKING .

The evaporator in the heater and A/C unit has a larger output than the evaporator for cooling the high-voltage battery. Depending on the version to cool the Electric Vehicle Battery -A2- /Hybrid Battery Unit -AX1- (hybrid battery), the expansion valve in front of this evaporator (the heat exchanger for cooling the high-voltage system components) is currently activated only from or up to a certain battery temperature by the respective control module, so that the exchange of energy via this evaporator does not increase, or only slightly. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function and refer to COOLING OUTPUT, CHECKING .

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 and fill the refrigerant circuit with the correct quantity of refrigerant (in the A/C compressor). Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A and REFRIGERANT R134A CAPACITIES, REFRIGERANT OIL AND APPROVED REFRIGERANT OILS .

Read the supporting information. Refer to SPECIFIED VALUES FOR REFRIGERANT CIRCUIT PRESSURES, VEHICLES WITH HEAT PUMP .

Read the supporting information. Refer to SPECIFIED VALUES FOR REFRIGERANT CIRCUIT PRESSURES, VEHICLES WITH HEAT PUMP .

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

If the expansion valve in the heater and A/C unit evaporator or the installed shut-off valve is malfunctioning (permanently closed or does not open sufficiently), the A/C compressor is actuated to maximum output and the low pressure drops to specification or below (compressor draws off refrigerant from low-pressure side). Since no (or little) the refrigerant can 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 and COOLING OUTPUT, CHECKING .

If the expansion valve for the evaporator for cooling the high-voltage components is faulty (or the function and activation is faulty) is always closed or does not open wide enough the A/C compressor is also activated with the maximum output (the required temperatures in the heat exchanger are not reached). The pressure on the low pressure side only then decreases to the specified value or lower, if no cooling output is needed at the same time in the front heater and A/C unit. The A/C compressor extracts the refrigerant from the low pressure side from both evaporators. Because no refrigerant can low over the expansion valve in the front heater and A/C unit and the cooling output in the evaporator for cooling the high voltage battery is not reached (there is a malfunction in the area of the evaporator for the cooling of the high voltage battery) the electric A/C compressor is activated with a higher speed. If not refrigerant can flow the pressure on the low pressure side falls under the specified value, high pressure may also not increase or only increase slightly due to the absence of energy. The same applies if a valve in the refrigerant circuit is not OK a malfunction in the incorporation of the evaporator for cooling the high-voltage battery in the high-voltage system refrigerant circuit or the pump or a valve installed there is not OK. Then the high-Voltage Battery Heat Exchanger is cooled, but the cooled coolant reached the high-voltage battery heat exchanger which should not be cooled. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function and refer to Coolant Circuit .

For additional information. Refer to SPECIFIED VALUES FOR REFRIGERANT CIRCUIT PRESSURES, VEHICLES WITH HEAT PUMP .

First, it is not necessary to clean the refrigerant circuit (flushing with refrigerant R134a. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ) in case of this complaint because generally only a small amount of moisture is in the system and this can be removed by a long evacuation.

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.

A malfunction on the Evaporator Vent Temperature Sensor -G263- or/and on the pressure/temperature sensor the can lead to the refrigerant circuit freezing-up. For this concern also pay attention to the measured values of the different pressure/temperature sensor in the refrigerant circuit. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function and refer to COOLING OUTPUT, CHECKING .

For additional information. Refer to SPECIFIED VALUES FOR REFRIGERANT CIRCUIT PRESSURES, VEHICLES WITH HEAT PUMP .

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. Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A . 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 the expansion valve for the evaporator for cooling the high-voltage components is faulty (or the function and activation is faulty) is always closed or does not open wide enough the A/C compressor is also activated with the maximum output (the required temperatures in the heat exchanger are not reached). The pressure on the low pressure side only then decreases to the specified value or lower, if no cooling output is needed at the same time in the front heater and A/C unit. The A/C compressor extracts the refrigerant from the low pressure side from both evaporators. Because no refrigerant can low over the expansion valve in the front heater and A/C unit and the cooling output in the evaporator for cooling the high voltage battery is not reached (there is a malfunction in the area of the evaporator for the cooling of the high voltage battery) the electric A/C compressor is activated with a higher speed. If not refrigerant can flow the pressure on the low pressure side falls under the specified value, high pressure may also not increase or only increase slightly due to the absence of energy. The same applies if a valve in the refrigerant circuit is not OK a malfunction in the incorporation of the evaporator for cooling the high-voltage battery in the high-voltage system refrigerant circuit or the pump or a valve installed there is not OK. Then the high-Voltage Battery Heat Exchanger is cooled, but the cooled coolant reached the high-voltage battery heat exchanger which should not be cooled. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function and refer to Coolant Circuit .

A malfunction on the Evaporator Vent Temperature Sensor -G263- or/and on the pressure/temperature sensor the can lead to this concern. Also pay attention to the measured values of the different pressure/temperature sensor in the refrigerant circuit. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function and refer to COOLING OUTPUT, CHECKING .

For additional information. Refer to SPECIFIED VALUES FOR REFRIGERANT CIRCUIT PRESSURES, VEHICLES WITH HEAT PUMP .

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.

For additional information. Refer to SPECIFIED VALUES FOR REFRIGERANT CIRCUIT PRESSURES, VEHICLES WITH HEAT PUMP .

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 for the evaporator in the A/C unit or for the evaporator for cooling the high-voltage components is faulty (always open), the evaporator temperature (in the front heater and A/C unit or in the evaporator for cooling the high-voltage components) is no longer regulated so that only refrigerant in gaseous state leaves the evaporator. 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 .

For additional information. Refer to SPECIFIED VALUES FOR REFRIGERANT CIRCUIT PRESSURES, VEHICLES WITH HEAT PUMP .

If the required cooling output on the evaporator in the front heater and A/C unit (and on the evaporator for cooling the high-voltage battery is OK) and there is a concern due to insufficient heating performance on the heat exchanger for the heat pump operation. The cause may be in the high-voltage system coolant circuit or in the engine coolant circuit. If the pumps and valves in the high-voltage system coolant circuit is not activated correctly or its function is not OK via the evaporator (heat exchanger) for the high-voltage system components not enough heat energy is absorbed from the coolant. If the pumps and valves in the engine coolant circuit are not activated correctly or are not functioning correctly, the absorbed heat energy, which is transferred via the heat exchanger for heat pump function, may not be delivered to the coolant which flows to the heater core in the heater and A/C unit. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding"  function and refer to Coolant Circuit .

For additional information. Refer to SPECIFIED VALUES FOR REFRIGERANT CIRCUIT PRESSURES, VEHICLES WITH HEAT PUMP .