What are the real reasons for compressor frosting

What are the real reasons for compressor frosting

Frosting at the return air port of a cold storage compressor is a common phenomenon in refrigeration systems.Piston Type Compressor Unit Generally, it does not immediately cause system problems, Screw Type Compressor Unit and minor frosting generally does not need to be addressed. If the phenomenon of frost formation is severe, the first step is to understand the cause of frost formation. Air Cooled Type Condenser Unit

Frost formation at the compressor return port:

Frost on the return air port indicates that the return air temperature of the compressor is too low. So what situation can cause the return air temperature of the compressor to be too low? Water Cooled Type Condenser Unit
If the volume and pressure of refrigerant of the same quality are changed, Evaporator Unit the temperature will have different performance. If the return air temperature of the compressor is low, it generally shows both low return air pressure and high refrigerant volume of the same volume. Mobile Cold Room The root cause of this situation is that the refrigerant flowing through the evaporator cannot fully absorb the heat required to expand to the predetermined pressure and temperature value. Refrigeration Project and Construction
1. The supply of liquid refrigerant to the throttle valve is normal, but the evaporator cannot absorb heat properly;

There are two factors that can cause this problem:

2. The evaporator is working normally to absorb heat, but the refrigerant supply to the throttle valve is too high, which means that the refrigerant flow rate is too high. We usually understand it as having too much refrigerant.

Due to the lack of fluorine, the compressor return air is frosted:

1. Due to the extremely low flow rate of refrigerant. Insufficient refrigerant expansion will not utilize the entire evaporator area, but will only form low temperatures locally in the evaporator. In some areas, rapid expansion due to insufficient refrigerant will cause local temperatures to be too low, leading to frost formation in the evaporator.

After partial frost formation, due to the formation of an insulation layer on the surface of the evaporator and the low heat exchange in that area, the refrigerant expansion is transferred to other areas, gradually causing the entire evaporator to frost or freeze. The entire evaporator forms an insulation layer, and then the expansion spreads to the compressor return pipe, causing the compressor return air to frost.

2. Due to the insufficient amount of refrigerant. The low evaporation pressure of the evaporator leads to a low evaporation temperature, which gradually causes condensation in the evaporator to form an insulation layer, and transfers the expansion point to the compressor return air, causing the compressor return air to frost.

Both of the above points will show evaporator frost before the compressor return air frosts.

In fact, in most cases, for frost phenomenon, just adjust the hot air bypass valve. Specific method: Open the rear end cover of the hot air bypass valve, and then use an No. 8 hex wrench to turn the adjusting nut clockwise. The adjustment process should not be too fast. Generally, pause for about half a turn, let the system run for a period of time, and then check the frost situation before deciding whether to continue the adjustment. After the operation is stable and the frost phenomenon of the compressor disappears, tighten the end cover.

Frosting at the cylinder head (severe crankcase frosting):

Frosting at the cylinder head is caused by a large amount of wet steam or refrigerant being sucked into the compressor. The main reasons for this situation are:

1. The opening of the thermal expansion valve is adjusted too large, causing the installation of the temperature sensing package to be incorrect or loose, resulting in the sensing temperature being too high and causing the valve core to open abnormally.

The thermal expansion valve is a direct acting proportional regulator that uses the superheat at the outlet of the evaporator as a feedback signal, compares it with a given superheat value, and generates a deviation signal to regulate the refrigerant flow entering the evaporator. It integrates a transmitter, regulator, and actuator.

According to different balancing methods, thermal expansion valves can be divided into two types: internal balancing thermal expansion valves and external balancing thermal expansion valves.

The opening of the thermal expansion valve is adjusted too large, the installation of the temperature sensing package is incorrect or the fixing is loose, resulting in the sensing temperature being too high and causing the valve core to open abnormally, causing a large amount of wet steam to be sucked into the compressor and leading to frost formation at the cylinder head.

If the superheat at the outlet of the evaporator is too high, the overheated section at the rear of the evaporator will be too long, and the cooling capacity will be significantly reduced; If the outlet superheat is too low, it may cause compressor liquid hammer or even frost on the cylinder head. It is generally believed that the expansion valve should be adjusted to a working superheat of 3 ℃ to 8 ℃ at the outlet of the evaporator.

2. The expansion valve is not tightly closed when the supply solenoid valve leaks or shuts down. Causing a large amount of refrigerant liquid to accumulate in the evaporator before startup. This situation can also easily cause compressor fluid shock!

3. There is too much refrigerant in the system. The liquid level in the condenser is higher, the condensation heat exchange area is reduced, and the condensation pressure increases. That is, the pressure in front of the expansion valve increases, and the amount of refrigerant flowing into the evaporator increases. The liquid refrigerant cannot completely evaporate in the evaporator. Therefore, the compressor sucks in wet steam, causing the cylinder head to cool or even frost, and may cause "liquid hammer". At the same time, the evaporation pressure will also be higher.