1Communication and composition of passenger car air-conditioning devices Bus air-conditioning devices usually consist of four basic parts: ventilation system, refrigeration system, heating system and automatic control system. The air conditioning unit of the passenger car is mixed into the vehicle at a certain flow rate by mixing a certain amount of fresh air outside the vehicle and the recirculated air inside the vehicle, and is filtered, cooled or heated, dehumidified or humidified, and the vehicle is delivered at a certain flow rate. The dirty air is discharged outside the vehicle, so that the humidity and temperature inside the vehicle are well maintained within the comfort range of the human body. Since the winter bus mainly adopts the heating method of the boiler or the electric heater, the refrigeration system of the air-conditioning device of the passenger car in summer is particularly important in ensuring the ride comfort of the passenger. The refrigeration system of a passenger car air conditioner generally consists of a compressor, an evaporator, a condenser, a throttling device, a drying filter, and a gas-liquid separator. 2 passenger car air conditioning unit refrigeration failure statistics air conditioning device failure caused by poor cooling effect, mainly caused by compressor aging, system leakage, filter blockage and other reasons. From the statistics, the leakage of the system due to leakage of the pipeline, the drying filter, the condenser, etc., accounted for 40.7%; and due to evaporator, condenser corrosion, compressor failure, system accessories aging The faults causing poor cooling of the system accounted for 59.3%. From the time of passenger car use in which the air conditioner failed, the passenger service life was 25.9% for 5 10 years, and 74.1% for 10 years or more. . 3 Analysis of the cause of the cooling failure Through the current vehicle inspection and treatment of the air conditioning unit refrigeration system failure, it is believed that the main causes of the poor cooling failure are as follows. 1) Refrigeration system leakage (low-voltage relay operation) (1) The air-conditioning device is used for a long time, the evaporator and condenser walls are thinned due to oxidation and corrosion, and local leakage occurs; (2) elbows in the evaporator and condenser The joint is prone to local high pressure, the joint is easily leaked or even broken due to corrosion and vibration; (3) The dry filter joint and its own weld are prone to leakage or breakage due to corrosion and vibration; (4) The refrigerant is circulated throughout the system. The interfaces (including the process tubes) are slowly leaked due to corrosion and oxidation. 2) High-voltage protection of refrigeration system (high-voltage relay action) (1) The evaporator and condenser fins are more oxidized and corroded, which affects the heat exchange between the evaporator and the condenser; (2) the compressor is used for a long time, the piston wears, and the valve plate The shutdown is not strict, affecting the efficiency of the compressor, and it is necessary to charge more refrigerant to make up for the poor efficiency of the compressor; (3) The evaporator and condenser are used for a long time, impurities and oil are generated in the system, affecting the evaporator and Condensate heat exchange; (4) Dry filter, distributor (throttle device) and other parts due to long use time, produce impurities and oil, blockage in the system, affecting the circulation of refrigerant. 3) The system is not cooled (compressed by the compressor) (1) The mechanical parts of the compressor are worn out, causing mechanical failures such as pulling cylinders, sticking cylinders, and jamming; (2) the compressor is used for a long time, the motor windings are aging, and the insulation is poor. Cause the compressor is broken and burned; (3) The compressor is overloaded, and the exhaust temperature is too high, causing the compressor to burn. 4) Poor cooling (insufficient cooling capacity) (1) Due to long use time, the filter is not cleaned in time, blocked by dust or debris, resulting in poor cooling; (2) The evaporator and condenser are used for a long time, because they are not timely Cleaning, fin ash, dirty lead to poor heat exchange, resulting in poor cooling; (3) due to high temperature setting or malfunction of the temperature controller, resulting in poor cooling; (4) due to evaporator icing, poor heat exchange And caused poor cooling. In order to further analyze the causes of poor cooling failures, we have a deeper understanding of the impact of the external environment and air conditioning unit status on the refrigeration system, and the organization detects the poor cooling failures found during operation and overhaul. Tested on passenger car YZ25G343255 (95 passenger car), external temperature 34, 4 compressors work normally after power-on, the cooling effect is obvious, the working current is about 10 A (normally about 8 A), test run 30 min, inside the car The temperature dropped from 34.5 to 25; when the test was performed again at 3 pm, the external temperature was 42. After the 4 compressors were operated for 10 minutes, the cooling fault lamps (4 fault lamps) were successively turned on, and a small amount of refrigerant was discharged. The compressor works, but the cooling effect is poor, the outlet air temperature is high, and the temperature inside the vehicle drops to 32 and does not decrease substantially. ! The air conditioning unit of the YZ25G343242 (95-year passenger car) refrigeration fault is tested on the test bench of the air-conditioning unit. The temperature between the test chambers is 35. When the refrigerant pressure (intake) is charged to 0.6 MPa (gauge pressure), the return air pipe Immediately dew condensation, return air temperature 19, compressor operating current is 10 A, return air temperature, pressure, working current is high (in the case of external temperature 35, the normal return steam temperature is 4 10 , the gauge pressure is 0. 46 0. 55 A, the compressor operating current is about 8. 5 A); a small amount of refrigerant is discharged, the refrigerant pressure (suction) to 0. 5 MPa, the compressor operating current is 9. 5 A, the return air does not condense, However, the cooling effect is poor. If the refrigerant continues to be charged, the operating current will exceed 10 A, and the return air temperature will decrease, but once the external temperature is high, the system will light the cooling fault light (high voltage relay action). Through the above tests on the air-conditioning unit with refrigeration failure, it can be seen that the air-conditioning device of the passenger car with an operation time of about 12 a is prone to refrigeration failure. Due to the long use time, the compressor, evaporator, condenser and other components are aging and corroding. When the external temperature is not high, the refrigeration effect is still good, but as the external temperature rises, the cooling state gradually deteriorates, when the external temperature When it reaches 40 and above, its refrigeration is even worse. 4 Suggestions (1) According to the iron letter <1994> No. 192? Regarding the notice issued by the issuing #, it is stipulated that when the air-conditioning unit is used for more than 12 years and the condition is bad, it must be replaced. In combination with the use of the Zhengzhou bus section, it is recommended to replace the air-conditioning unit when the vehicle is used for more than 10 years. During the repair period, the unit is in poor condition and the replacement unit or its key components, such as compressors, evaporators, condensers, etc., are used. (2) According to the train running line, the trains that drive to the higher temperature in the south, especially the trains that have reached or exceeded 40 in the summer outside temperature, should be as good as possible. Avoid adverse reactions caused by poor high temperature cooling. (3) Equipped with a fully-featured air-conditioning unit test bench (can guarantee a constant temperature of 35 to ensure that the refrigeration performance test can also be carried out in winter). During the bus depot and section repair, the refrigeration performance of the air-conditioning unit is guaranteed to ensure the quality of the air-conditioning unit. . (4) Strengthen the maintenance of the air-conditioning unit of the passenger car, and open the cover of the air-conditioning unit during the annual spring and autumn renovation of the passenger car, especially before the air conditioning unit is put into use in the spring, and the evaporator and condenser are put into operation. Clean the dust to ensure good heat transfer. (5) During the daily operation of the passenger car, the filter screen of the air conditioner should be cleaned and dusted regularly to ensure good ventilation and heat transfer effect of the air conditioner, and ensure the performance of the air conditioner. (6) In order to ensure the timely treatment of air-conditioning unit failures, it is recommended that each vehicle segment reserve a certain amount of key components of air-conditioning equipment according to the passenger vehicle allocation, and establish a quota management system to meet the needs of passenger car operation and regular maintenance. 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