How is high pressure created? In order to maintain the normal cycle of automobile air conditioners, the gaseous refrigerant that evaporates and absorbs heat must be re-liquefied into a liquid refrigerant, and liquefaction (condensation) needs to meet the two conditions of temperature and pressure and is indispensable.
Temperature conditions: During condensation, the temperature of the gaseous refrigerant must be lowered below the critical temperature. Such as the critical temperature of R134a is 101 ??. Above this temperature, no matter how high the pressure is, it cannot condense.
Pressure conditions: During condensation, the system must maintain a certain condensation pressure, otherwise condensation cannot be achieved.
The vaporized gaseous refrigerant is of low temperature and low pressure. At this time, its temperature meets the condensation requirements, but because its pressure is too low, it cannot meet the re-condensation requirements. Therefore, we must increase its pressure to meet the pressure conditions for condensation. The compressor is the device used to increase the pressure of the refrigerant.
The compression process is: the compressor sucks low-temperature and low-pressure refrigerant from the suction port. At this time, since the temperature of the compressor is higher than that of the refrigerant vapor, the compressor transfers heat to the refrigerant, and The temperature of the compressor is lowered, but with the compression of the gas in the compression chamber, the temperature of the gas rises sharply. When the compression is over, the temperature of the gas is much higher than the temperature of the compressor, and the high-temperature gas will transfer heat back to the compressor. machine and warm up the compressor. The temperature of the gas at the end of compression is affected by the following factors: 1) Compression ratio (compression ratio = exhaust pressure / suction pressure) 2) adiabatic index of the gas, the adiabatic index of the gas is a constant, determined by the properties of the gas, the adiabatic index The higher the temperature, the higher the exhaust temperature (pressure). For example, the adiabatic index of R22 will be higher than that of R134a, so the exhaust pressure and condensing pressure of R22 will be higher. 3) Suction temperature. If the superheat of the gaseous refrigerant is high, the suction temperature will be high.
If the heat absorbed by the refrigerant is greater than the heat released at the end of its compression, the temperature of the compressor will drop and frost will occur; if the heat absorbed by the refrigerant is less than the heat released at the end of its compression The heat released will increase the temperature of the compressor and cause the compressor to become hot and hot.
The high temperature and high pressure gaseous refrigerant discharged from the compressor, when it first enters the condenser, cannot be liquefied and condensed well due to its high temperature and does not meet the temperature conditions for condensation. With the heat exchange of the gaseous refrigerant in the condenser, the temperature of the refrigerant decreases, at this time it will condense into a liquid state, and the volume will decrease, and the space occupied by the condenser will also decrease accordingly. The process of reducing the relative volume of the occupied condenser is also a process of reducing the relative pressure, and the process of heat dissipation and cooling determines the speed of this process. However, it is not enough to reduce the condensing volume. There is another factor that determines the condensing pressure (high pressure), that is, the opening degree (throughput) of the expansion valve, because the gaseous refrigerant discharged from the compressor port is discharged to the liquid refrigerant. The discharge from the expansion valve is a dynamic balance. If the opening is too small, the discharge of the expansion valve is less than the discharge of the compressor, which will increase the pressure. If the opening is too large, the opposite will occur, and the condensing pressure has a certain proportional relationship to the opening of the thermal expansion valve.
In summary, the high pressure of an automobile air conditioner is affected by 1) the compression ratio 2) the adiabatic index of the gas 3) the suction temperature 4) the compressor temperature 5) the heat dissipation performance conditions of the condenser 6) the expansion valve It is determined by factors such as the matching performance and other factors. If you encounter high voltage programming in the future, you can find a solution from the above factors.