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Why does cold storage compressor frost

November 30, 2021

1. Compressor return air is frosted
Due to the small amount of refrigerant, the low evaporation pressure of the evaporator leads to a low evaporation temperature, which will gradually cause condensation in the evaporator to form a heat insulation layer and transfer the expansion point to the return air of the compressor to cause frosting of the return air of the compressor. The above two points will show the frosting of the evaporator before the return air of the compressor is frosted.

2. The cylinder head is frosted (when it is severe, the crankcase is frosted)
1. The opening of the thermal expansion valve is adjusted too large, the temperature sensing bulb is installed incorrectly or the fixing is loose, so that the temperature felt is too high and the valve core opens abnormally.
2. The liquid supply solenoid valve leaks or the expansion valve is not closed tightly when the machine is shut down, causing a large amount of refrigerant liquid to accumulate in the evaporator before starting. The temperature relay is used in conjunction with the solenoid valve to control the storage temperature.
3. When starting the compressor, the suction stop valve is opened too large or opened too early.
4. When there is too much refrigerant in the system, the liquid level in the condenser is higher, and the condensation heat exchange area is reduced, which increases the condensation pressure, that is, the pressure before the expansion valve increases, and the amount of refrigerant flowing into the evaporator increases, and liquid refrigeration The agent cannot evaporate completely in the evaporator, so the compressor sucks in wet steam, the cylinder hair is cold or even frosted, which may cause "liquid hammer", and the evaporation pressure will also be high.

Defrosting method:
In fact, in most cases, for frosting, you only need to adjust the hot gas bypass valve. The specific method is to open the rear end cover of the hot gas bypass valve, and then use a No. 8 Allen key to turn the inner adjusting nut clockwise. The adjustment process is not necessary. If it is too fast, generally you will pause after a half-turn, and let the system run for a period of time to see the frosting situation before deciding whether to continue the adjustment. After the operation is stable and the frosting of the compressor disappears, tighten the end cover.
For models below 15 cubic meters, since there is no hot gas bypass valve, if the frosting phenomenon is serious, the take-off pressure of the condensing fan pressure switch can be appropriately increased. The specific method is to find the pressure switch first, remove the small piece of the pressure switch's adjusting nut, and then turn it clockwise with a Phillips screwdriver. The entire adjustment needs to be carried out slowly. Adjust a half circle to see the situation before deciding whether to adjust.