Buick air conditioning intermittent cooling troubleshooting
A Shanghai GM Buick car equipped with R134a fully automatic air conditioning. During driving, the cold air output of the air conditioning outlet gradually decreases, and after a period of time, it returns to normal.
First, the air-conditioning system is operated. After a period of time, the intermittent refrigeration failure phenomenon described by the customer does occur. When the cooling capacity is reduced, observe the working condition of the compressor and find that the compressor can always pull in. Connect the air conditioner pressure gauge, test the high and low pressure end pressure in the system, the value is normal. The vehicle-specific detector TECH2 is used for detection, no fault code is stored, and the data about the air conditioner (mainly the air conditioner pressure signal) in the ECU is read, and no abnormality is found.
After inquiring the owner, I learned that the car had been charged with refrigerant in the repair shop outside because the air conditioner was not cool, so the author suspected that the refrigerant of the car was not pure enough. After testing the refrigerant composition through the refrigerant purity analyzer, it is found that 28% of R12 exists in the system. Because the refrigerant added to the Buick car air-conditioning system should be R134a, the refrigerant in the system is evacuated, and the compressor pressure control valve is replaced, the air-conditioning pipeline is purged with nitrogen and evacuated to fill the pure R134a refrigerant, and the air conditioner is turned on again Test, troubleshooting.
Buick cars are equipped with variable displacement air-conditioning compressors. When the air conditioning system is working, the air conditioning control system does not collect the temperature signal of the evaporator air outlet, but controls the compression ratio of the compressor to automatically adjust the air outlet temperature according to the pressure change signal in the air conditioning pipeline.
In the whole process of cooling, the compressor is always running, and the adjustment of the cooling intensity is completely dependent on the pressure regulating valve installed inside the compressor to control. When the pressure in the high-pressure end of the air conditioning line is too high, the pressure regulating valve shortens the stroke of the piston in the compressor to reduce the compression ratio, which will reduce the cooling intensity. When the pressure in the high-pressure end drops to a certain level and the pressure in the low-pressure end rises to a certain level, the pressure regulating valve increases the piston stroke to increase the cooling strength.
Because R12 is mixed into the refrigerant of the vehicle air conditioning system, the pressure in the system is poorly controlled and the cooling strength is increased. After working in this state for a period of time, the low temperature causes frost on the outer wall of the evaporator, and there is no wind in the air outlet of the air conditioner. When the frost on the outer wall of the evaporator melts, the system returns to normal. Because the excessively low temperature has changed the elastic coefficient of the internal spring of the pressure regulating valve, the pressure regulating valve should also be replaced.
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