Troubleshooting of air-conditioning compressors for new energy vehicles

What are the general failures of the air-conditioning compressors of new energy vehicles and how to repair them? A sports utility vehicle with a mileage of approximately 48,000 km. The user reported that the instrument panel suddenly lit up when the car was driving, the power was interrupted, and there was no response when stepping on the accelerator pedal. The car used inertia to coast to the side of the road to stop.

Inspection and analysis: Communicate with the user when the vehicle breaks down, park the vehicle on the side of the road first, and do not turn off the electricity and wait for the trailer. After the vehicle was towed into the factory, it was found that there were many malfunction lights in the dashboard, and the vehicle could not drive when switched to D gear. After powering off and powering on again, the fault still exists, that is, the fault is continuous. We use a dedicated diagnostic instrument to test the vehicle, and the results have many communication fault codes.

Judging from the diagnosis result, the vehicle's network communication is faulty, and all fault codes that appear do not have a certain pattern. Analyze the interrelationship between the fault codes, look up the CAN network communication circuit diagram of the whole car in the maintenance manual, and find that each control unit communicates with each other through the CAN bus. That is to say, the control unit transmits its own information to the CAN network, and at the same time receives the information it needs or is related to itself from the network, that is, the CAN bus transmission is bidirectional. In addition, the diagnostic instrument reads the fault codes of all control units through the OBD interface.

From this analysis, the resistance between the No. 2 and No. 3 terminals of the OBD interface measured by a multimeter is 60Ω (terminal resistance), which is normal, that is, there is no short circuit between the 2 CAN wires; respectively measure the voltage between the No. 2 and No. 3 terminals to the ground , The results are all around 5.1V, and the normal value is 2.4~2.6V, indicating that the CAN network is short-circuited with a certain power supply line. The reasons for this result may be: control unit failure, CAN bus failure. Where should so many control units start? At this point, the inspection ideas are in trouble. After careful consideration, combined with actual experience, I decided to adopt an awkward method to analyze control units with greater possibility of failure, such as control units such as VCU, BMS, BCM, and MCU, and disconnect their connectors one by one, and then check whether there is water ingress. Corrosion and other abnormalities, if necessary, use the replacement test method to verify. When the low-pressure connector of the air-conditioning compressor was disengaged, it was found that the connector had obvious signs of corrosion due to ingress of water.

From the above process analysis, it can be seen that the fault is caused by the interference of the CAN network voltage caused by the water in the air-conditioning compressor connector.