[Knowledge of Auto Repair]-Auto Air Conditioner

Car Air ConditionerAnalysis of the reasons why the high pressure is normal, the low pressure is high, and the air conditioning effect is not good

The air conditioners of many cars, especially those that have been used for a period of time, often have a high pressure of 14-15 kg (at most only slightly higher and no more than 17 kg), but the low pressure is higher (above 2.5 kg). At this time, the air conditioning effect It will get worse, and this phenomenon has been bothering us, making many repairmen helpless. What is the cause of this, and what better way to solve it? Any car with a high low pressure pressure (above 2.5 kg) will always be accompanied by unsatisfactory air conditioning effects. The reasons for the low low pressure pressure are:

1) Heat load: The greater the heat load, the temperature of the evaporating box will increase, and the evaporation pressure will also increase. The heat load is related to the ambient temperature. The hotter the day, the higher the ambient temperature, the heat load The larger is also, the general middle and low-end cars will have the evaporation pressure (low pressure) in the hot summer. As the temperature rises, the evaporation temperature also rises, and the temperature of the air outlet begins to rise, and the driver feels that there is no air conditioning effect when the weather is cold. Well, of course, for the high-level design with large enough cooling capacitycar, This effect is very small. And the heat load is not transferred by human will.

2) The opening of the expansion valve: When the suction volume is constant, the larger the opening of the expansion valve, the higher the low pressure pressure. The effect of the car air conditioning is ultimately the size of the cooling capacity, and the outlet temperature and air volume /Pipe, evaporation temperature, the amount of refrigerant entering the evaporation box, etc., and the evaporation temperature is related to the evaporation pressure, whencompressorWhen the inspiratory volume is constant (andRotating speedRelated), the larger the opening of the expansion valve, the more refrigerant enters the evaporator, and the refrigerant vapor generated by evaporation cannot becompressorQuick suction produces a certain low pressure, so even though the refrigerant is evaporating in a large amount, the evaporation temperature is still high. Low pressure does not help the improvement of the refrigeration effect, but if the expansion valve opening is large and the low pressure is too high, the refrigeration effect is poor, then the opening of the expansion valve should be reduced? Reduce the opening of the expansion valve, It is possible to reduce the low pressure. At this time, the evaporation temperature will drop sharply, and even cause a small area of ​​frost. However, because the opening degree is reduced, the amount of refrigerant flowing into the evaporator will also decrease, so although there is some evaporator temperature It is very low, but the evaporator on more area is not cool, and the total cooling capacity will not increase.