1. Refrigerant leakage: After the refrigerant leaks in the system, the cooling capacity is insufficient, the suction and exhaust pressures are low, and the intermittent "squeaking" airflow sound much larger than usual can be heard at the expansion valve. There is no frost or a small amount of floating frost on the evaporator. If the expansion valve hole is enlarged, the suction pressure still does not change greatly. After the shutdown, the equilibrium pressure in the system is generally lower than the saturation pressure corresponding to the same ambient temperature.

2. Excessive charging of refrigerant after maintenance: The amount of refrigerant charged in the refrigeration system after maintenance exceeds the capacity of the system, and the refrigerant will occupy a certain volume of the condenser, reduce the heat dissipation area, and reduce the cooling effect. The suction and exhaust pressure are generally higher than the normal pressure value, the evaporator is not frosted solidly, and the cooling in the warehouse is slow.

3. There is air in the refrigeration system: the air in the refrigeration system will reduce the refrigeration efficiency. The obvious phenomenon is that the suction and exhaust pressures increase (but the exhaust pressure has not exceeded the rated value), and the compressor outlet to the condenser inlet The temperature increases significantly. Due to the presence of air in the system, the exhaust pressure and exhaust temperature increase.

4. Low compressor of condensing unit efficiency: The low efficiency of the refrigeration compressor refers to the fact that the actual exhaust volume decreases and the refrigeration capacity decreases accordingly when the working conditions remain unchanged. This phenomenon mostly occurs in compressors that have been used for a long time. The wear and tear of the compressors are large, the matching clearance of each component is large, and the sealing performance of the air valve is reduced, resulting in a decrease in the actual exhaust volume.

5. The frost on the surface of the evaporator is too thick: the long-term use of the cold storage evaporator should be defrosted regularly. If it is not defrosted, the frost layer on the evaporator pipeline will be thicker and thicker. When the entire pipeline is wrapped into a transparent ice layer, It will seriously affect the heat transfer, causing the temperature in the warehouse to fall below the required range.
6. There is refrigerated oil in the evaporator pipeline: During the refrigeration cycle, some refrigerated oil remains in the evaporator pipeline. After a long time of use, if there is a lot of residual oil in the evaporator, it will seriously affect its heat transfer effect. , the phenomenon of poor cooling occurs.
7. The refrigeration system is not smooth: due to the poor cleaning of the refrigeration system, after a period of use, the dirt gradually accumulates in the filter, and some meshes are blocked, which reduces the flow of refrigerant and affects the refrigeration effect. In the system, the expansion valve and the filter at the suction port of the compressor are also slightly blocked.
8. The expansion valve hole is frozen and blocked: the main components in the refrigeration system are not properly dried, the vacuuming of the entire system is not complete, and the moisture content of the refrigerant exceeds the standard.
9. Dirty blockage at the filter screen of the expansion valve: When there are too many coarse powdery dirt in the system, the entire filter screen will be blocked, and the refrigerant cannot pass through, resulting in no cooling. Knock on the expansion valve, and sometimes cooling can be achieved with some refrigerant. It is recommended that the filter be removed for cleaning, drying, and reinserted into the system.