Possible Deviation From Specified Value During The Pressure Test (1 Of 12)

Possible Deviation from Specified Value During the Pressure Test
High pressure remains constant or increases only slightly (above pressure with engine stopped), Low pressure quickly drops to target value or lower. The required cooling output is not attained in the heater and A/C unit evaporator and in the evaporator for cooling the high-voltage components.
Possible causes for the deviation from specified value and their solutions
One in or on the removed refrigerant circuit pressure/temperature sensor or temperature sensor sends incorrect values. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function. Refer to Component Location Overview - A/C System . Not enough refrigerant in refrigerant circuit Activation of the A/C compressor or a valve installed in the refrigerant circuit is faulty. -- Check the measured values of the different pressure/temperature sensor and temperature sensor when operating the A/C system, and replace the components with incorrect measured values. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function. Refer to Component Location Overview - A/C System . If no errors can be detected, evacuate the refrigerant.-- Extract refrigerant from the refrigerant circuit. Refer to REFRIGERANT CIRCUIT, DISCHARGING .-- If the extracted refrigerant quantity is significantly less than the specified capacity (more that 100 g (3.5 oz) less). Refer to Technical Data , and look for leaks and correct. Refer to LEAKS, FINDING .-- The extracted refrigerant quantity corresponds approximately to the specified capacity, check the activation of the A/C compressor and the installed shut-off valve, if not malfunction is determined, replace the expansion valve for the evaporator in the heater and A/C unit. Refer to Refrigerant Circuit . -- Depending on the results, service the activation or replace the faulty component (A/C compressor, shut-off valve, expansion valve). Refer to the Refrigerant Circuit .
Final Procedures
-- Charge the refrigerant circuit. Refer to REFRIGERANT CIRCUIT, CHARGING .-- Repeat the test. Refer to ELECTRICALLY-DRIVEN A/C COMPRESSOR, CHECKING PRESSURE WITH A/C SYSTEM SWITCHED ON .

NOTE:

To determine the possible cause of a malfunction, different routines are stored in the basic setting of the control module (for example in the thermal management control module) which activate these functions: "cooling the A/C system", "heat pump", and "cooling the components of the high-voltage system". Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function. Refer to Refrigerant Circuit .

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 clean the refrigerant circuit (flush with refrigerant R1234yf). One of these malfunctions may arise due to a constriction or a blockage in the refrigerant circuit. Refer to Refrigerant Circuit and REFRIGERANT CIRCUIT, CLEANING .

On vehicles with the "heat pump" function and/or "high-voltage battery cooling" in not all operating conditions is the A/C system high pressure on the service connection of the high pressure side. 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 . 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. Refer to 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/hybrid battery unit (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. 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/dryer cartridge must be replaced. After cleaning the refrigerant circuit (flushing with refrigerant R134a) and fill it with the correct quantity of refrigerant oil in the circuit (in the A/C compressor). Refer to REFRIGERANT CIRCUIT, CLEANING and Technical Data .