Small refrigerators, including movable refrigerators, generally have a capacity of less than 100 tons. The evaporator of the cold storage adopts the exhaust pipe type or the combined type of the cold fan, which is composed of the compressor unit (water-cooled or air-cooled), the throttle expansion valve, etc. to form a complete refrigeration system. Most of the compressors are semi closed, the larger system is also open, the smaller system is fully closed. R22 is the common refrigerant.

Generally, the most common operation faults of refrigeration system in cold storage are: the cooling temperature drops slowly, the operation condition caused by system blockage is abnormal or unable to operate, etc.

The cooling temperature of the cold storage drops slowly, which is mainly caused by improper operation and adjustment, among which the adjustment of expansion valve is the most critical. If the opening degree of expansion valve is small, the flow and pressure of refrigerant will be less; if the opening degree of expansion valve is large, the flow and pressure of refrigerant will be more. 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 are too low. However, due to the decrease of flow and pressure into the evaporator, the evaporation speed is slowed down, the refrigerating capacity per unit volume (time) is reduced, and the refrigerating efficiency is reduced. On the contrary, if the outlet pressure of expansion valve is too high, the corresponding evaporation pressure and temperature are too high. The flow and pressure entering the evaporator are increased. Due to the excess evaporation of liquid, the over damp gas (or even liquid) is sucked in by the compressor, which causes the wet stroke (liquid hammer) of the compressor, which makes the compressor unable to work normally, resulting in a series of bad working conditions and even damage the compressor. The opening degree of expansion valve shall be adjusted according to the current storage temperature, i.e. under the pressure corresponding to the storage temperature. If the storage temperature is - 10 ℃, the evaporation temperature of the cold storage should be about 5 ℃ lower than the storage temperature, that is - 15 ℃, and the corresponding evaporation pressure is about 0.3MPa (absolute pressure). Because of the pressure loss, the regulating pressure is basically reflected in the suction pressure of the compressor.

The regulating expansion valve must be carried out carefully and patiently. The regulating pressure must be generated by heat exchange boiling (evaporation) between the evaporator and the storage temperature, and then enter the suction chamber of the compressor through the pipeline to reflect on the pressure gauge, which requires a time process. Every time the expansion valve is adjusted, it usually takes 10-15 minutes to stabilize the regulating pressure of the expansion valve on the suction pressure gauge, and the regulation cannot be carried out too quickly. The suction pressure of the compressor is the main basis parameter for the expansion valve to regulate the pressure.

The technical performance of expansion valve directly affects its normal operation. It is easy to block the filter screen and leak the temperature sensing agent. Causes the adjustment reaction not to be sensitive, the adjustment loses control or cannot adjust and so on. When the inlet of the expansion valve is frosted (or the valve cover is frosted), the temperature of the liquid inlet pipe is lower than that of the normal temperature, or even condensation; the suction pressure of the compressor is lower than the corresponding pressure under the storage temperature, the operation temperature and exhaust temperature of the machine are high, and the cooling temperature drops slowly or does not drop, which is enough to indicate that the filter screen of the expansion valve is blocked, and there is dirty blockage or ice blockage.

Treatment method: close the main liquid supply valve, open the compressor for operation. When the suction pressure is stable below 0, close the discharge valve of the compressor, and stop the compressor at the end of closing (fluorine collection is completed). Disassemble the liquid inlet of the expansion valve, take out the filter screen, clean it and replace it, replace the infusion drying filter agent or filter, check the performance of the infusion solenoid valve and restore it (check and clean it). Open the exhaust by-pass port of the compressor (other states are still in the state of fluorine Collection), start up and operate, let the air from the main valve of liquid supply to the compressor body be drawn out from the exhaust by-pass port, when the suction pressure is stable below 0 (after pumping), close the exhaust by-pass port, open the exhaust valve and main valve of liquid supply of the compressor, and the system will resume operation.

If the expansion valve itself works normally, it is just the blockage caused by too much water or dirt in the system, which causes serious ice blockage or dirty blockage and makes the system work abnormally. The temperature of the liquid pipe in front of the expansion valve is lower than that of the normal temperature, or even condensation. There is no temperature reaction in the pipeline behind the valve. The suction pressure of the compressor is below 0, the operating temperature and exhaust temperature of the machine are high, or even knocking sound occurs The refrigeration temperature does not drop and the operation condition is poor.

The excessive water content of the system is mainly caused by the incomplete maintenance vacuum at ordinary times; the low pressure caused by leakage continues to operate under negative pressure and inhales moisture; the system is put aside for a long time after being disassembled; the moisture of the parts is sticky; the moisture content of the refrigerant is excessive; the condenser tube of the water-cooled condenser is broken, etc. The main reason for excessive fouling in the system is the deposition of iron oxides in the exhaust evaporator and water-cooled condenser and other pollutants in the system with the working medium circulation.

To deal with the above faults, the blowdown and water removal operation of the system can be carried out at the same time. The specific method: connect the bypass port of the low-pressure valve of the compressor to discharge fluorine. When the pressure is set to 0 gauge, it is deemed that the working medium of the system has been discharged. Open a bypass port with the same diameter as the discharge pipe at the lowest position of the evaporation discharge pipe, and install the corresponding fluorine valve; install the three-way port with the same diameter and relevant valve at the outlet of the condenser (the condenser pipe of the water-cooled condenser shall be repaired or replaced in advance if it is broken). Open the compressor (the water supply valve of the water-cooled condenser shall be opened), draw in air from the suction bypass port, compress and boost the pressure through the compressor, stop the compressor when the pressure rises to 1.2MPa gauge pressure, and quickly open the bypass valve at the lowest part of the evaporation discharge pipe and the liquid outlet tee of the condenser, and the compressed air shall follow