The common operating faults of refrigeration system in cold storage are: slow cooling temperature drop, abnormal operating conditions caused by system blockage, etc.The slow drop of refrigeration temperature in cold storage is mostly caused by improper operation adjustment, in which the adjustment of expansion valve is the key. When the opening of the expansion valve is small, the flow rate of refrigerant passing through is less and the pressure is low; The larger the opening degree of the expansion valve, the more the refrigerant passes through and the higher the pressure.According to the thermodynamic properties of refrigerant, 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 are too low. However, due to the decrease of the flow rate and pressure entering the evaporator, the evaporation speed is slowed down, the refrigeration capacity per unit volume (time) is reduced, and the refrigeration efficiency is reduced.If the outlet pressure of the expansion valve is too high, the corresponding evaporation pressure and temperature are too high. The flow rate and pressure entering the evaporator are increased. Due to the excess evaporation of liquid, the gas (even liquid) with excessive moisture is sucked in by the compressor, which causes the compressor to fail to work normally, resulting in a series of bad working conditions and even damage to the compressor.The opening degree of the expansion valve should be adjusted according to the warehouse temperature at that time, that is, under the pressure corresponding to the warehouse temperature.Example: The storage temperature is -10 degrees, and the evaporation temperature of the cold storage should be about 5 degrees lower than the storage temperature, that is, -15 degrees, and the corresponding evaporation pressure is about 0.96 kg (R22). Because of the pressure loss, the regulating pressure is basically reflected in the suction pressure of the compressor.Adjusting the expansion valve must be done carefully and patiently. It takes a long time to adjust the pressure, and then it will enter the suction cavity of the compressor through the pipeline and be reflected on the pressure gauge after heat exchange boiling (evaporation) between the evaporator and the reservoir temperature.Every time the expansion valve is adjusted, it usually takes 10~15 minutes to stabilize the adjustment pressure of the expansion valve on the suction pressure gauge, and the adjustment should not be rushed. The suction pressure of compressor is the main parameter for adjusting the pressure of expansion valve.The technical performance of expansion valve directly affects whether it can adjust and operate normally. Usually, the filter screen is blocked and the temperature sensitive agent leaks easily. The adjustment response is insensitive, and the adjustment is out of control or unable to be adjusted. When frost appears at the inlet of the expansion valve (or the valve cover is also frosted), the temperature of the liquid inlet pipe is lower than normal temperature, or even condensation occurs.Example: The suction pressure of the compressor is lower than the corresponding pressure at the storage temperature, the operating temperature and exhaust temperature of the machine are high, and the cooling temperature drops slowly or not, which may be due to the blockage of the filter screen of the expansion valve, dirty blockage or ice blockage (or refrigerant leakage).Treatment method:1. Close the main valve for liquid supply, start the compressor operation, and when the suction pressure is stable below 0, close the exhaust valve of the compressor, and stop the compressor operation at the end of closing (after fluorine collection).2. Disassemble the liquid inlet of the expansion valve, take out the filter screen and put it back after cleaning, and replace the infusion drying filter or filter. Check the performance of the infusion solenoid valve and then restore it (after cleaning).3. Open the exhaust bypass port of the compressor (others are still in the state of fluorine collection), start the machine, and let all the air from the main liquid supply valve to the compressor be pumped out from the exhaust bypass port. When the suction pressure is stable below 0 (after pumping), close the exhaust bypass port, open the exhaust valve and main liquid supply valve of the compressor, and the system will resume operation.If the expansion valve itself works normally, it is only because of the blocking phenomenon caused by too much water or dirt in the system, resulting in serious ice blocking or dirty blocking, which makes the system work abnormally. The temperature of the liquid pipe in front of the expansion valve is lower than normal temperature, or even condensation, and the pipeline behind the valve has no temperature response. The suction pressure of the compressor is below 0, the machine operating temperature and exhaust temperature are high, and even knocking sound appears, and the refrigeration temperature does not drop, resulting in bad operating conditions.

Too much water in the system:1. The maintenance vacuum is not thorough at ordinary times;2. Leakage causes low pressure to continue running under negative pressure, and moisture is inhaled;3. The system has been put on hold for too long after being disassembled;4, the parts are moist and sticky;5. The refrigerant contains excessive water;6. The condenser tube of the water-cooled condenser is broken;The main reasons for excessive fouling in the system are the precipitation of iron oxides and other pollutants in the system with the circulation of working fluid in the tube evaporator and water-cooled condenser.

Inspection of compressor compression efficiency: close the intake and exhaust valve of the compressor, open the exhaust bypass port (multi-purpose port) and start the compressor operation. The low pressure of the compressor will soon form a vacuum, and the outlet of the exhaust bypass port will gradually become smaller, and soon no gas will be discharged, and the operation noise will gradually become smaller, and there is no oil discharged from the exhaust bypass port. After the exhaust bypass port (multi-purpose port) is closed and stopped, the low pressure vacuum of the compressor will not rise quickly, and the high and low pressure will wait for 10-15 minutes.If gas has been discharged from the exhaust bypass of the compressor, or lubricating oil will be brought out (ejected), it is enough to show that the compressor has poor compression performance, the air tightness of the valve is not strict, and the wear gap between the operating part of the cylinder and the oil ring is too large. Need to be repaired. This is a basic, simple and practical method to check the compression efficiency and air tightness test of compressor.In addition, the oil and air discharging operation of the system should be carried out frequently or regularly to improve the heat exchange performance and refrigeration effect of the heat exchanger. Because of its high viscosity, refrigeration oil is usually adsorbed on the inner surface of pipelines or containers, forming an oil film layer. Especially on the low pressure side (from the outlet of expansion valve to the inlet of compressor), the viscosity of oil is higher due to the low temperature, and the oil film layer formed is of course larger, which increases the thermal resistance of heat exchangers (evaporator and condenser), affects the heat transfer performance and reduces the refrigeration effect. The more oil in the system, the greater this disadvantage, so it is very unfavorable for refrigeration.The presence of air or other non-condensable gases in the system will increase the condensation pressure and temperature, increase the power consumption, increase the operating temperature of the compressor, and reduce the refrigeration efficiency. The tube evaporator can use the sewage outlet opened at the lower part to discharge oil; Generally, the manufacturers of the lower liquid outlet of the combined evaporator of the air cooler will have an oil (sewage) outlet.Both oil draining and air venting operations should be carried out under the static state of system shutdown, and air venting should also be carried out when the temperature is low, so that the effect will be better. There is no special venting equipment for the system, and the venting generally chooses the outlet on the high pressure side. Evaporator tubes of cold storage and finned tubes of air cooler should be defrosted in time (regularly) to ensure their good heat transfer effect.