The temperature in the cold storage can't come down. Please check these points

There are two main reasons for the lack of refrigeration dosage (insufficient refrigerant in the system), insufficient refrigerant charge, and lack of refrigerant circulation At this time, it is only necessary to fill in enough refrigerant Another reason is that there is a lot of refrigerant leakage in the system In order to catch up with this situation, it is necessary to find out the leakage point first, check the connection of each pipeline and valve, find out the leakage part and fill in enough refrigerant after repairing Lack of refrigeration capacity (improper adjustment of expansion valve) insufficient refrigeration dosage in the system will directly affect the refrigerant flow into the evaporator When the expansion valve is opened too large, the expansion valve is not properly adjusted or blocked, the refrigerant flow is too large, the evaporation pressure and temperature will also increase, and the temperature in the warehouse will slow down At the same time, when the expansion valve is opened too small or blocked, the refrigerant flow is also reduced, the cooling capacity of the system is also reduced, and the temperature of the warehouse will also slow down Generally, the refrigerant flow of expansion valve can be determined by observing the evaporation pressure, evaporation temperature and frosting of suction pipe The blocking of expansion valve is an important factor affecting refrigerant flow, and the main causes of blocking of expansion valve are ice blocking and dirty blocking Ice blockage: due to the poor drying effect of the dryer and the moisture contained in the refrigeration system, when flowing through the expansion valve, the temperature drops below 0 ℃, the moisture in the refrigerant forms into ice and blocks the orifice of the throttle valve It is because the filter screen at the inlet of the expansion valve contains more dirt, the refrigerant is smooth and blocked, forming a blockage There is more air or refrigerant oil in the evaporator Once more refrigerant oil is attached to the inner surface of the heat transfer tube of the evaporator, the heat transfer coefficient will be reduced Similarly, if there is more air in the heat transfer tube, the heat transfer area of the evaporator will be reduced, the heat transfer efficiency will be significantly reduced, and the temperature in the warehouse will be reduced accordingly Therefore, in the daily operation and maintenance, it is necessary to timely remove the oil contamination on the inner surface of the heat transfer tube of the evaporator and exhaust the air in the evaporator, so as to improve the heat transfer efficiency of the evaporator The decrease of heat transfer effect (too thick frost or too much dust on the surface of the evaporator) is mainly caused by too thick frost or too much dust on the surface of the evaporator Because the surface temperature of the evaporator in the cold storage is mostly lower than 0 ℃, another important reason for the slow decline of the temperature is the low heat transfer efficiency of the evaporator However, the humidity in the warehouse is relatively high, and the moisture in the air is easy to frost or even freeze on the surface of the evaporator, which affects the heat transfer effect of the evaporator In order to prevent the outer frost layer of the evaporator from being too thick, it is necessary to defrost it on schedule Here are two simple defrosting methods: defrosting: stop the compressor, open the warehouse door, let the temperature rise, and restart the compressor after the frost layer melts automatically Frost flushing: after the goods in the warehouse are moved out, directly wash the surface of the drain pipe of the evaporator with hot tap water to make the frost layer dissolve or fall off In addition to the frost too thick will lead to poor heat transfer effect of the evaporator, the surface of the evaporator due to the temporary not clean dust too thick, its heat transfer efficiency will be significantly reduced It leads to a large loss of cooling capacity (cold storage due to poor thermal insulation or sealing function) and poor thermal insulation and insulation effect The poor heat insulation function is due to the insufficient thickness of the insulation layer of pipes, warehouse insulation walls, etc It is mainly caused by improper thickness selection of thermal insulation layer in design or poor quality of thermal insulation data in construction In addition, during construction and use, the thermal insulation and moisture-proof function of thermal insulation data may be damaged, which may cause the thermal insulation layer to be damp, deformed, or even eroded The thermal insulation capacity of thermal insulation data will be reduced, the cooling loss of warehouse will be increased, and the temperature drop will be slowed down significantly Another important reason for the large cold loss is the poor sealing function of the warehouse, and more hot air intrudes into the warehouse from the leaking place Generally, if there is condensation on the sealing strip of the warehouse door or the sealing part of the insulation wall of the cold storage, it means that the sealing is not tight In addition, frequent opening and closing of the warehouse door or more people entering the warehouse together will also increase the cold loss of the warehouse Try to prevent opening the warehouse door and large amount of hot air from entering the warehouse Of course, when the warehouse enters the inventory frequently or the purchase quantity is too large, the heat load increases sharply, and it usually takes a long time to cool down to the designated temperature The efficiency of the compressor is low, and the refrigeration capacity can not meet the requirements of the warehouse load The cylinder sleeve, piston ring and other components are severely worn With the increase of the fit clearance, the sealing function will be correspondingly reduced, the gas transmission coefficient of the compressor will also be reduced, and the refrigeration capacity will be reduced When the refrigerating capacity is less than the heat load of the warehouse, the temperature of the warehouse will decrease slowly The refrigeration capacity of the compressor can be roughly determined by observing the suction and discharge pressure of the compressor If the refrigeration capacity of the compressor drops, the common method is to replace the cylinder sleeve and piston ring of the compressor If the replacement still fails to work, other factors shall be taken into consideration, and even the disassembly inspection shall be carried out to eliminate the fault factors.