The causes and solutions of frosting on the expansion valve of industrial chillers

I believe many friends will encounter such problems when using industrial chillers. The expansion valve is frosting! So why does it frost? How to solve this problem?

Discussion and analysis
1. Some people will first consider whether the expansion valve is blocked or opened too small.
2. Some people may also consider whether the fan is faulty.
3. Of course, some people will analyze the direction of frost formation.
There are mainly two types:
Frost gradually forms from the compressor return port towards the evaporator direction. Frost forms in the direction from the expansion valve to the evaporator.
Analyze the differences between these two types of frosting, and the reasons are opposite. Therefore, when troubleshooting, not only should the expansion valve, evaporator, and return pipe frost, but also the direction of frost should be distinguished.

The return air port is beginning to frost, mainly analyzed from the following two aspects:
1. The reason for refrigerant is that more refrigerant enters the evaporator, resulting in incomplete evaporation. Therefore, the return airway is still evaporating and absorbing the heat from the suction tube, so the return airway is first frosted.
The reasons are as follows:
(1) Excessive refrigerant;
(2) Excessive opening of expansion valve;

2. In terms of evaporator, the evaporator cannot absorb heat normally, or the cold generated by the evaporator cannot be taken away, which will lead to incomplete evaporation. The refrigerant continues to evaporate and absorb heat in the return air duct, causing frost to form in the return air duct. The appearance shows normal or slightly lower reflux temperature and pressure. The return port of the compressor is gradually frosting towards the evaporator. After a long period of time, all parts from the reflux port of the compressor to the evaporator, throttle valve to the evaporator froze, and finally low pressure appeared.

The reasons are as follows:
(1) Check if the air filter is clean;
(2) Check if the water pump is functioning properly;
(3) Is the evaporator clean;
(4) Check if the cooling fan is blocked in the air supply system;

The expansion valve began to frost behind the expansion valve, mainly analyzed from the following three aspects:
1. Insufficient refrigerant (leakage): The return liquid temperature of the condenser is high but the pressure is not high, and frost gradually forms in the direction of the evaporator starting from the throttle valve.
2. The opening of the expansion valve is too small, and the return liquid temperature and pressure of the condenser are normal or slightly low. Frost gradually forms in the direction of the evaporator starting from the throttle valve.
3. Check the liquid microscope to see the refrigerant. If the bubbles flip severely, it may be a system leak; The refrigerant in a liquid microscope does not or rarely bubbles. It may be due to the expansion valve opening being too small or blocked. Generally speaking, there is a large temperature difference before and after blockage.