Repair case of abnormal noise of automobile air-conditioning compressor

Today, I will share with you a repair case about abnormal noise of automobile air-conditioning compressor. Trouble phenomenon: a car with a mileage of about 80,000 km. The air-conditioning and refrigeration performance of this car is not good.

Fault diagnosis: After picking up the vehicle, first test the vehicle to verify the fault phenomenon. Turn on the ignition switch, start the engine, turn on the AC switch of the air conditioner, and a little cold air blows out from the air outlet of the air conditioner. The air-conditioning system of the car is not completely uncooled, it only starts to cool after the air-conditioning has been running for a long time, and the cooling effect is extremely poor. The temperature of the air outlet of the air conditioner was continuously monitored, and the digital thermometer showed that the temperature of the air outlet was 11.9°C. After the air conditioner has been running for a period of time, it is found that the air outlet of the air conditioner is gradually blowing natural wind, and the compressor has abnormal noise, and the abnormal noise becomes more and more obvious as the engine speed increases. After turning off the AC switch of the air conditioner, the abnormal noise disappears immediately. Use a pressure gauge to test the pressure of the air-conditioning pipeline and find that the pressure on the high pressure side is 980kPa and the pressure on the low pressure side is 300kPa. Obviously, the working pressure of the air conditioning system is abnormal. The duty cycle signal was 85% detected by the detector, the current of the air-conditioning compressor regulating valve was 0.80A, and no abnormality was found in the signal control. Check the condenser water tank and found that its surface is dirty.

The quality and quantity of the refrigerating oil in the air-conditioning piping system were tested with a special inspection cotton for refrigerating oil, and it was found that the refrigerating oil had been blackened, acidified, and the amount of oil was seriously depleted. Based on this, it can be preliminarily determined that the compressor is poorly lubricated due to severe deterioration of the refrigerating oil and insufficient oil, which causes abnormal compressor noise. The compressor has slight abrasion and reduced work efficiency, and the surface of the condenser water tank and evaporator is dirty, which causes poor air-conditioning refrigeration performance. Based on the above inspection, analysis and judgment, the maintenance personnel have formulated the following maintenance plan for the air-conditioning system of the vehicle: Clean the entire air-conditioning system, add new refrigerating oil and refrigerant; Clean the dirt on the surface of the condenser water tank; Clean the evaporator box Surface dirt, and replace the air-conditioning filter element. After the owner signs and confirms the maintenance plan, the maintenance personnel will carry out the construction item by item in accordance with the air conditioning maintenance standard construction work process. When cleaning the air-conditioning pipes, it was found that the old refrigerating oil in the malfunctioning car was dark and turbid in color. The amount of old refrigerating oil recovered was about 80 mL and the refrigerant was about 4508. After cleaning the air-conditioning pipes, the maintenance personnel in strict accordance with the requirements of the maintenance manual added 7 525±25g refrigerant and 130±10mL refrigerating oil to the faulty car. After completing the quantitative filling of new refrigerant and refrigerating oil, start the engine and turn on the air conditioner for performance testing. The high-pressure side pressure is 1 400kPa, the low-pressure side pressure is 200kPa, the air outlet temperature is 4.1°C, and the duty cycle signal is 90%. The air conditioning compressor regulating valve current is 0.85A. All parameters are normal, and the air conditioning system is operating normally. However, after about 5 minutes of normal operation, abnormal noise appeared again in the compressor part, and the abnormal noise gradually increased from small to loud, even louder than the sound before maintenance, but the abnormal sound disappeared immediately after turning off the AC switch. The maintenance staff had to turn off the air conditioner first and perform technical analysis. After refilling refrigerant and refrigerating oil, all parameters of the air-conditioning system returned to normal, and the abnormal noise not only did not disappear, but the sound was louder. It can be judged that the air conditioner compressor has a mechanical failure or poor lubrication.

Communicate with the car owner again. The car owner said in a puzzled manner that it was only occasional abnormal noise before, how could it become a continuous abnormal noise after repairing? In this regard, our analysis and explanation from a technical perspective is that there have been signs of damage before, but it has not yet reached the level of completely unusable. The decline in air-conditioning refrigeration performance and occasional abnormal noise are proofs. After preliminary maintenance, the air-conditioning refrigeration performance has been completely restored. However, the abnormal noise caused by mechanical wear of the compressor can only be completely solved by replacing the compressor. In the end, the owner said that if the replacement of the compressor could not completely solve the problem, he would not pay any repair costs, and expressed that he was very dissatisfied with the repair. Fortunately, the owner has agreed to replace the compressor. After re-recovering the refrigerant and refrigerating oil, the maintenance personnel found that there was very little lubricating oil inside the compressor during the dismantling of the compressor, and only less than 20mL of refrigerating oil was poured out when the oil drain was opened, which obviously did not meet the technical requirements. It has been detected that the amount of refrigerating oil is insufficient before maintenance, and new refrigerating oil has been refilled according to the technical requirements during maintenance. Why is there still insufficient oil in the compressor? If the compressor is replaced with a new one, will the same phenomenon of insufficient lubricating oil in the compressor? Will there be abnormal noise again? Regarding this, the maintenance personnel were at a loss. For the sake of prudence, the maintenance personnel finally decided to disassemble the compressor of the malfunctioning car to check whether there is indeed mechanical damage inside. After disassembly, it was found that the inside of the compressor had been cleaned very cleanly. Although the piston and the compressor cylinder were slightly worn, it did not affect normal use. To this end, the maintenance personnel re-recall and sort out every detail of the previous maintenance, and carefully study the structure and working principle of the electronically controlled variable displacement compressor, so as to truly find the source of the abnormal noise of the compressor.

For automobile air-conditioning compressors, as long as the engine is started, even if the AC switch is turned off, the input shaft is always rotating. If refrigerant and refrigerating oil are lacking, the compressor will be damaged even in winter when refrigeration is not required. When the maintenance personnel cleaned the air-conditioning system pipeline, the refrigerating oil that was originally inside the compressor was also washed out, and when the refrigerant and refrigerating oil were added later, the compressor was not separately filled with refrigerating oil, which resulted in There is still a lack of refrigerating oil inside the compressor, and there is a problem of insufficient lubrication. After finding the cause of the failure, the maintenance personnel installed the compressor, and separately filled 80 mL of refrigerating oil from the compressor oil inlet. Refill the air-conditioning system with refrigerant and refrigerating oil, let it stand for about 5 minutes to allow the refrigerant and refrigerating oil to fully fuse, and then add an air-conditioning synergistic protective agent after "three off and three on" according to the operating process. In order to repair the slight wear and tear of the compressor. Start the engine, turn on the AC switch, the abnormal noise of the air-conditioning compressor disappears completely, and the refrigeration performance of the air-conditioning is tested, and all the parameters are back to normal. So far, the air-conditioning failure of the malfunctioning car has been completely eliminated.