Frosting reason of refrigeration compressor in constant temperature and humidity test chamber

I frosting at the return port of the compressor indicates that the temperature of the return gas of the compressor is too low, so what will cause the temperature of the return gas of the compressor to be too low? The refrigerant flowing through the evaporator can not fully absorb the heat needed for its expansion to the predetermined pressure and temperature value, resulting in low temperature, pressure and volume value of the return gas There are two reasons for this problem: ◆ the liquid refrigerant supply of throttle valve is normal, but the evaporator can not absorb heat normally to supply refrigerant expansion ◆ the heat absorption of evaporator works normally, but the refrigerant supply of throttle valve is too much, that is to say, the refrigerant flow is too much We usually understand that there is too much fluorine, that is to say, too much fluorine will also cause low pressure 2 The return gas of the compressor is frosted due to the lack of fluorine ◆ due to the extremely small flow of the refrigerant, the refrigerant will flow out of the expandable space at the rear end of the throttle valve automatically and start to expand Most of us see that the frosting of the liquid separating head at the rear end of the expansion valve is often caused by the lack of fluorine or insufficient flow of the expansion valve, which is too cold Medium expansion will not use the whole evaporator area, but will form a low temperature in some parts of the evaporator Due to the rapid expansion of a small amount of refrigerant in some areas, the local temperature is too low, resulting in frosting of the evaporator ◆ after local frosting, due to the formation of thermal insulation layer on the surface of the evaporator and the low heat exchange in this area, the expansion of refrigerant will be transferred to other areas, and gradually the whole evaporator will be frosted or frozen The whole evaporator will form a thermal insulation layer, so the expansion will spread to the air return pipe of the compressor, resulting in the frosting of the air return of the compressor ◆ due to the small amount of refrigerant and the low evaporation pressure of the evaporator, the evaporation temperature will be low, which will gradually lead to the condensation of the evaporator to form a heat insulation layer, and the expansion point will be transferred to the return gas of the compressor, which will cause the return gas of the compressor to frost The above points will show the evaporator frosting before the compressor return gas frosting III frost at the cylinder head (severe frost in crankcase) is always caused by a large amount of wet steam or refrigerant inhalation into the compressor The main reasons for this situation are as follows: ◆ the opening of thermal expansion valve is adjusted too large, the temperature sensing package is installed incorrectly or fixed loose, so that the temperature is too high and the valve core is abnormally opened The opening of the thermal expansion valve is adjusted too large, the temperature sensing package is installed incorrectly or fixed loose, so that the temperature is too high and the valve core is opened abnormally, so that a large number of wet steam is sucked into the compressor and the cylinder head is frosted ◆ when the liquid supply solenoid valve leaks or the expansion valve is not closed tightly during shutdown, a large amount of refrigerant liquid has accumulated in the evaporator before startup ◆ when starting the compressor, the compressor is too large, or the suction stop valve is opened too large or too early ◆ when there are too many refrigerants in the system, the liquid level in the condenser is high, the condensation heat exchange area is reduced, and the condensation pressure is increased, that is, the pressure in front of the expansion valve is increased, and the amount of refrigerant flowing into the evaporator is increased The liquid refrigerant in the evaporator cannot Completely evaporated, so the compressor inhales wet steam, the cylinder hair is cold or even frosted, which may cause "liquid hammer", and the evaporation pressure will also be high