Possible Deviation From Specified Value During The Pressure Test (3 Of 9)

Possible Deviation from Specified Value during the Pressure Test
Required cooling output is not attained The high pressure does not increase or only increases slightly above pressure with engine stopped The low pressure does not drop or drops only slightly
Possible causes for the deviation from specified value and their solutions
The A/C compressor is not driver or not driven with the specified speed. -- Check the A/C compressor drive (via the belt or drive unit). Refer to A/C Compressor . The activation of the A/C Compressor Regulator Valve -N280- (the A/C Clutch -N25-) is faulty. -- Check the activation of the A/C Compressor Regulator Valve -N280- (and the A/C Clutch -N25-) and if necessary service. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function of the A/C compressor. A/C Compressor Regulator Valve -N280- or A/C compressor faulty -- Check the function of the A/C Compressor Regulator Valve -N280- and if necessary remove the A/C Compressor Regulator Valve -N280- and if necessary check for contamination. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function of the A/C system. Refer to COMPONENTS, REPLACING .-- Replace the A/C Compressor Regulator Valve -N280- or the A/C compressor. Refer to COMPONENTS, REPLACING .-- If there is dirt in the refrigerant circuit clean the refrigerant circuit (flush with refrigerant R1234yf), expansion valve and desiccant bag/dryer cartridge (or replace the reservoir/receiver/dryer). Refer to COMPONENTS, REPLACING , Refrigerant Circuit and REFRIGERANT CIRCUIT, CLEANING . Constriction or obstruction in refrigerant circuit (for example, inside the refrigerant line between the service connection "low pressure side" and the A/C compressor). -- Run hand over refrigerant circuit to check for differences in temperature. Refer to Refrigerant Circuit . 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 Refrigerant Circuit .
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:

Make sure that the A/C compressor (the A/C compressor shaft) is actually being driven by the belt pulley/drive unit for this complaint (pay attention to the overload protection). Refer to A/C Compressor .

For some engines, A/C compressor are being introduced that, in addition to the A/C Compressor Regulator Valve -N280-, an A/C Clutch -N25- is being attached to the belt pulley. Make sure that the A/C Clutch -N25- is actually being actuated and the A/C compressor (A/C compressor shaft) is being driven by the belt pulley. Refer to Refrigerant Circuit and to the Parts Information.

In no malfunction is determined for this concern, clean the refrigerant circuit (flush with refrigerant R1234yf). Refer to REFRIGERANT CIRCUIT, CLEANING .

Check the measured values of the Evaporator Vent Temperature Sensor -G263- and the activation of the A/C Compressor Regulator Valve -N280-. If the measured value of the Evaporator Vent Temperature Sensor -G263- malfunctions the evaporator can ice over or the cooling output is not reached. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function of the A/C system.

If the A/C system function is not OK after repeating the test, for example after replacing expansion valve, clean the refrigerant circuit by flushing using the refrigerant R1234yf. Refer to REFRIGERANT CIRCUIT, CLEANING . Then replace the A/C compressor and reservoir/receiver/dryer (or dryer cartridge). Refer to Refrigerant Circuit .

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 the low pressure drops to value in graph or below (the A/C compressor draws off refrigerant from low-pressure side). Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function of the A/C system. As however refrigerant cannot flow via the expansion valve, the cooling output is not attained and high pressure may also not increase or only increase slightly due to the absence of energy conversion.