The car air conditioner is running and there is no wind, and the pipe is still frosting. It may be a problem here
Yesterday, some netizens asked such a question: The air volume of the air outlet began to drop after 40 to 50 minutes of driving the car with the air conditioner, and the cooling effect also decreased. And a pipe from the air-conditioning compressor to the dashboard is also frosted. From the picture, this is the frosting of the low pressure pipe of the air conditioner.
The low-pressure pipe is the pipe from the evaporator to the compressor in the center console of the car, which is generally thicker. From the picture provided by the subject, it can be clearly seen that the surface of the tube has been frosted.
The picture above is a schematic diagram of an automobile air conditioning system. The compressor compresses the vaporous refrigerant into a high-temperature and high-pressure gaseous state, and then comes to the condenser, where the temperature of the refrigerant decreases and condenses into a medium-temperature and high-pressure liquid state. Then it is filtered by the drying system and comes to the expansion valve. The expansion valve can be understood as a nozzle. After the expansion valve is the evaporator, the refrigerant before the expansion valve is of medium temperature and high pressure, but after passing through the expansion valve, the refrigerant is injected from the small hole When it comes out, it becomes a mist and enters the evaporator. The pressure in the evaporator is much lower, and the refrigerant starts to expand and evaporate to absorb heat, resulting in low temperature in the evaporator. The gaseous refrigerant returns to the compressor through the low pressure pipe.
According to the principle of automobile air-conditioning system, we know that the low-pressure pipe is flowing with vapor and low-temperature refrigerant, so this pipe is cool to the touch, but this temperature is not enough to make the pipe frost. The pipe frost indicates that the refrigerant in the evaporator is too much. Too much, part of the refrigerant continues to evaporate and absorb heat in the back section of the evaporator near the low-pressure pipe. The main reasons are as follows:
1.Expansion valve failure
We have all used carburetor cleaner. This thing is a liquid in the bottle, and it evaporates into a gas soon after spraying out, and it will produce low temperature. The bottle of carburetor cleaner is equivalent to the high-pressure pipeline before the expansion valve of the automobile air conditioning system, and the nozzle of the carburetor cleaner is equivalent to the expansion valve. When we tap the nozzle, the flow of cleaning agent is low, and the sprayed cleaning agent evaporates quickly. But if we press it harder, the cleaning agent will spray out a lot, and it will take longer to evaporate.
The same is true for the expansion valve of automobile air conditioner. It can adjust the flow of refrigerant. When the temperature of the evaporator is high, the injection flow of refrigerant is large, and when the temperature of the evaporator is low, the injection flow of refrigerant is small. If a problem with the expansion valve causes the refrigerant to evaporate when a large amount of refrigerant is injected into the evaporator, a part of the refrigerant will run to the back of the evaporator or even enter the low-pressure pipe to evaporate, so low-pressure pipes will produce sufficient frost in the low-pressure pipe.
2.The evaporator temperature sensor signal is abnormal
Because the evaporator is essentially a radiator, the refrigerant changes from liquid vaporization and heat absorption into a vapor state, resulting in low temperature. The air flow passes through the gap of the evaporator, and the heat is absorbed and becomes cold air. Because there is a lot of condensed water on the surface of the evaporator when the air conditioner is working, when the temperature is low to a certain level, the condensed water will frost and cause the airflow channel of the evaporator to be blocked. Therefore, there is a temperature sensor on the evaporator, whose signal is directly transmitted to the ECU. When the evaporator temperature is close to the frosting temperature, the ECU will stop the compressor. If the ECU cannot get this signal or the signal is abnormal, the evaporator will easily frost. Generally, the reason for this phenomenon is the failure of the temperature sensor itself or the line failure.
3.Too much refrigerant
Too much refrigerant sometimes causes frost in the low pressure pipe. The principle can be understood like this: too much refrigerant causes the system pressure to be too high, which causes the expansion valve flow to exceed the normal flow, a large amount of mist refrigerant enters the evaporator, and some refrigerant that is too late to evaporate will enter the low pressure pipe and continue to evaporate in the low pressure pipe , Resulting in low-pressure pipe frost.
Although the car air conditioning system is very complicated, we can try to analyze some common failure causes after we understand its operating principle.
