Possible deviation from specified value during the pressure test (8 Of 9)

Possible deviation from specified value during the pressure test
The A/C compressor noise (particularly after switch-on) The required cooling performance is obtained. High pressure normal or too high, The low pressure is normal or too high (the specified value is not always reached),
Possible causes for the deviation from specified value and their solutions
The activation of the A/C Compressor Regulator Valve -N280- is faulty. -- Check the activation of the A/C Compressor Regulator Valve -N280- and if necessary service. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system. Check the function of the A/C Compressor Regulator Valve -N280- and if necessary replace the A/C Compressor Regulator Valve -N280- and check for damage. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system and refer to COMPONENTS, REPLACING and Refrigerant Circuit (vehicle-specific Service Information). Replace the A/C Compressor Regulator Valve -N280- or the A/C compressor. Refer to COMPONENTS, REPLACING and A/C Compressor (vehicle-specific Service Information). If there is dirt in the refrigerant circuit clean the refrigerant circuit (flush with refrigerant R1234yf) and the expansion valve and desiccant bag/dryer cartridge (or replace the reservoir/receiver/dryer). Refer to REFRIGERANT CIRCUIT, CLEANING , COMPONENTS, REPLACING and Refrigerant Circuit (vehicle-specific Service Information). Too much refrigerant or refrigerant oil in the refrigerant circuit -- Extract refrigerant from the refrigerant circuit. Refer to REFRIGERANT CIRCUIT, DISCHARGING .-- If the extracted refrigerant quantity is substantially greater (more than 100 g) than the specified capacity. (refer to Technical Data (vehicle-specific Service Information), there is too much refrigerant in the refrigerant circuit. Fill the refrigerant circuit and repeat the test.-- If the extracted refrigerant quantity meets the specified capacity is only slightly greater than the specified capacity (maximum 100 g) (refer to Technical Data (vehicle-specific Service Information) too much refrigerant oil is in the refrigerant circuit. Clean the refrigerant circuit (flush with refrigerant R1234yf) (refer to REFRIGERANT CIRCUIT, CLEANING ) fill with the correct quantity of refrigerant and refrigerant oil and repeat the test. Expansion valve malfunctioning. If a shut-off valve installed in the refrigerant circuit does not open or opens incorrectly. Refer to Refrigerant Circuit (vehicle-specific Service Information). -- If equipped, check the function of the installed shut-off valve. Refer to Refrigerant Circuit (vehicle-specific Service Information).-- Replace the expansion valve and desiccant bag/dryer cartridge (or reservoir/receiver/dryer). Refer to COMPONENTS, REPLACING and Refrigerant Circuit (vehicle-specific Service Information). A/C compressor faulty. -- If no malfunction can be determined on a component and the extracted refrigerant quantity corresponds to the specifications, clean the refrigerant circuit (flush with refrigerant R1234yf). Refer to REFRIGERANT CIRCUIT, CLEANING . If when cleaning the refrigerant circuit no excessive amount of refrigerant oil is determined, replace the A/C compressor. Refer to COMPONENTS, REPLACING , COOLING OUTPUT, CHECKING (vehicle-specific Service Information) and A/C Compressor (vehicle-specific Service Information).
Final Procedures
-- Charge the refrigerant circuit. Refer to REFRIGERANT CIRCUIT, CHARGING .-- Repeat the test. Refer to MECHANICALLY DRIVEN A/C COMPRESSOR, CHECKING PRESSURE WITH A/C SYSTEM SWITCHED ON .

NOTE:

This fault may also be caused by too much refrigerant oil in the refrigerant circuit. Overfilling with refrigerant oil can occur if, for example, the compressor has been replaced without adjusting the quantity of refrigerant oil. If there is too much refrigerant oil in the refrigerant circuit, clean the refrigerant circuit (flush with refrigerant R1234yf). REFRIGERANT CIRCUIT, CLEANING

If the expansion valve (or a present shut-off valve) is faulty (constantly closed or does not open far enough), the A/C Compressor Regulator Valve -N280- is actuated to maximum output and low pressure drops to value in graph or below (the A/C compressor draws off refrigerant from low-pressure side). As the refrigerant cannot flow via the expansion valve, if 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, and refer to Refrigerant Circuit (vehicle-specific Service Information).