The most common operational faults of the refrigeration system in cold storage are slow decrease in refrigeration temperature, system blockage causing abnormal operating conditions or inability to operate.

The slow decrease in refrigeration temperature in cold storage is often caused by improper operation and adjustment, among which the adjustment of the expansion valve is the most critical. The opening degree of the expansion valve is small, resulting in less refrigerant flow and lower pressure; The larger the opening degree of the expansion valve, the greater the flow rate of refrigerant passing through, and the higher the pressure. According to the thermodynamic properties of refrigerants, the lower the pressure, the lower the corresponding temperature; The higher the pressure, the higher the corresponding temperature. According to this law, if the outlet pressure of the expansion valve is too low, the corresponding evaporation pressure and temperature will also be too low. However, due to the decrease in flow rate and pressure entering the evaporator, the evaporation rate slows down, the refrigeration capacity per unit volume (time) decreases, and the refrigeration efficiency decreases. On the contrary, if the outlet pressure of the expansion valve is too high, the corresponding evaporation pressure and temperature will also be too high. The flow and pressure entering the evaporator increase, and due to the excess evaporation of liquid, the excess moisture gas (or even liquid) is sucked into the compressor, causing the wet stroke (liquid hammer) of the compressor, which makes the compressor unable to work normally, resulting in a series of harsh working conditions and even damaging the compressor. The opening degree of the expansion valve should be adjusted according to the current storage temperature, that is, adjusted under the pressure corresponding to the storage temperature.

Common faults and troubleshooting methods in cold storage

If the storage temperature is -10 degrees, check the "Thermal Properties Table" of R22 refrigerant, and the corresponding absolute pressure is 0.363MPa The evaporation temperature of the cold storage should be about 10 degrees lower than the storage temperature, which is -20 degrees, and the corresponding evaporation pressure is 0.251MPa absolute pressure; The suction pressure of the compressor is generally slightly higher than the evaporation pressure due to the pressure loss and superheat of the suction pipe (depending on the length and insulation effect of the pipeline). At this point, the regulating pressure of the expansion valve should be reflected in the suction pressure of the compressor, similar to the evaporation pressure, which is around 0.151MPa gauge pressure (absolute pressure -0.1MPa).

Adjusting the expansion valve must be done carefully and patiently. Adjusting the pressure must go through the evaporator and the storage temperature to generate heat exchange boiling (evaporation), and then enter the compressor suction chamber through the pipeline to reflect on the pressure gauge, which requires a time process. It usually takes 10-15 minutes to stabilize the regulating pressure of the expansion valve on the suction pressure gauge after each adjustment of the expansion valve. The adjustment should not be done too quickly. The suction pressure of the compressor is the main parameter for adjusting the pressure of the expansion valve.