Possible Deviation from Specified Value during the Pressure Test (4 Of 9)

Possible Deviation from Specified Value during the Pressure Test
Required cooling output is not attained The high pressure increases above specification The low pressure quickly drops to target value or lower
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. Constriction or obstruction in refrigerant circuit Expansion valve malfunctioning If a shut-off valve installed in the refrigerant circuit does not open or opens incorrectly. Refer to Air Conditioning (1 Of 3) / Air Conditioning (3 Of 3) (vehicle-specific Service Information). -- If equipped check the function of the installed shut-off valve. Refer to Air Conditioning (1 Of 3) / Air Conditioning (3 Of 3) (vehicle-specific Service Information).-- Run hand over refrigerant circuit to check for differences in temperature. Refer to Air Conditioning (1 Of 3) / Air Conditioning (3 Of 3) (vehicle-specific Service Information). If on a component differences in temperature is determined, because the hose or pipe are kinked or constricted, replace this component. If there is a blockage or no malfunction can be determined, clean the refrigerant circuit (flush with refrigerant R1234yf). Refer to REFRIGERANT CIRCUIT, CLEANING .-- Replace the expansion valve and desiccant bag/dryer cartridge (or reservoir/receiver/dryer). Refer to COMPONENTS, REPLACING and Air Conditioning (1 Of 3) / Air Conditioning (3 Of 3) (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:

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

If the expansion 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. Refer to Air Conditioning (1 Of 3) / Air Conditioning (3 Of 3) (vehicle-specific Service Information).

If there is too much refrigerant oil in the circuit, the A/C compressor must be emptied and the desiccant bag (the dryer cartridge) or the receiver/receiver/dryer must be replaced. After cleaning (flushing with refrigerant R1234yf) fill the refrigerant circuit with the correct quantity of refrigerant oil. Refer to REFRIGERANT CIRCUIT, CLEANING , APPROVED REFRIGERANT OILS AND REFRIGERANT OIL CAPACITIES (vehicle-specific Service Information) and Air Conditioning (1 Of 3) / Air Conditioning (3 Of 3) (vehicle-specific Service Information).

If the specified value when repeating the check is still not reached and on the refrigerant circuit no malfunction can be determined, clean the refrigerant circuit (flush with refrigerant R1234yf). Refer to REFRIGERANT CIRCUIT, CLEANING .