It is a common phenomenon that the temperature of cold storage can't drop and it drops slowly. This paper briefly analyzes the reasons for the slow temperature drop in cold storage, hoping to bring some help to the work of colleagues in cold storage.1, cold storage due to poor heat insulation or sealing performance, resulting in large cold loss!The poor thermal insulation performance of cold storage is due to the insufficient insulation thickness of pipes and warehouse insulation walls, and the poor thermal insulation and insulation effect, which is mainly caused by improper selection of insulation thickness in design or poor quality of insulation materials in construction. In addition, in the process of construction and use, the thermal insulation performance of thermal insulation materials may be destroyed, which may lead to the insulation layer being affected with moisture, deformation and even erosion, and its thermal insulation capacity will decrease, and the loss of cold storage capacity will increase, which will obviously slow down the temperature drop. Another important reason for the large cooling loss is the poor sealing performance of the warehouse, and more hot air invades the warehouse from the air leakage. Generally, if dew condensation occurs at the sealing strip of the warehouse door or the sealing part of the heat 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 avoid opening the warehouse door to prevent a lot of hot air from entering the warehouse. Of course, when the stock is frequently stocked or the stock quantity is too large, the heat load increases sharply, and it usually takes a long time to cool down to the specified temperature.2. The surface of the evaporator in the cold storage is frosted too thick or accumulated too much dust, which reduces the heat transfer effect.Another important reason for the slow temperature drop in cold storage is the low heat transfer efficiency of evaporator, which is mainly caused by the thick frost layer or excessive dust accumulation on the surface of evaporator. Because the surface temperature of evaporator in cold storage is mostly below 0℃, and the humidity in warehouse is relatively high, the moisture in the air is easy to frost or even freeze on the surface of evaporator, which affects the heat transfer effect of evaporator. In order to prevent the surface frost layer of evaporator from being too thick, it is necessary to defrost it regularly. Here are two simple defrosting methods: ① Stop the machine to defrost. That is, stop the compressor, open the warehouse door, let the warehouse temperature rise, and restart the compressor after the frost layer melts automatically. ② Frosting. After the goods in the warehouse are moved out, the surface of the evaporator tube is directly washed with tap water with high temperature to dissolve or fall off the frost layer. In addition to frosting too thick will lead to poor heat transfer effect of evaporator, the surface of evaporator is too thick due to long-term cleaning, and its heat transfer efficiency will also decrease obviously.3. The area of evaporator (air cooler) in cold storage is not enough.4. There is more air or refrigeration oil in the evaporator of cold storage, which reduces the heat transfer effect.Once more refrigeration oil is attached to the inner surface of the heat transfer tube of the cold storage evaporator, its heat transfer coefficient will decrease. Similarly, if there is more air in the heat transfer tube, the heat transfer area of the evaporator will decrease, its heat transfer efficiency will also decrease obviously, and the temperature drop rate of the warehouse will slow down accordingly. Therefore, in daily operation and maintenance, attention should be paid to timely removing the oil stain on the inner surface of the evaporator heat transfer tube and exhausting the air in the evaporator to improve the heat transfer efficiency of the evaporator.5. The throttle valve of the cold storage is improperly adjusted or blocked, and the refrigerant flow is too large or too small.Improper adjustment or blockage of the throttle valve in cold storage will directly affect the refrigerant flow entering the evaporator. When the throttle valve is opened too much, the refrigerant flow will be too large, the evaporation pressure and temperature will also increase, and the temperature drop rate of the warehouse will slow down; At the same time, when the throttle valve is too small or blocked, the refrigerant flow will also decrease, the refrigeration capacity of the system will also decrease, and the temperature drop rate of the warehouse will also slow down. Generally, the refrigerant flow rate of throttle valve can be judged by observing evaporation pressure, evaporation temperature and frosting of suction pipe. Throttle blockage is an important factor affecting refrigerant flow, and the main causes of throttle blockage are ice blockage and dirty blockage. Ice blocking is due to the poor drying effect of the dryer, and the refrigerant contains moisture. When it flows through the throttle valve, the temperature drops below 0℃, and the moisture in the refrigerant forms ice and blocks the throttle valve hole. Dirty blockage is due to the accumulation of more dirt on the filter screen at the inlet of throttle valve, and the poor circulation of refrigerant leads to blockage.6. The refrigeration dose in the cold storage system is insufficient and the refrigeration capacity is insufficient.There are two main reasons for the lack of refrigerant circulation in cold storage. First, the refrigerant charge is insufficient. At this time, just add enough refrigerant. Another reason is that there is a lot of refrigerant leakage in the system. In this case, we should first find the leakage point, focus on checking the joints of various pipes and valves, and find out the leakage parts and repair them before charging enough refrigerant.7. The compressor is inefficient, and the refrigeration capacity cannot meet the warehouse load requirements.Due to the long-term operation of the compressor, the cylinder liner, piston ring and other parts are seriously worn, and the fitting clearance increases, so the sealing performance will decrease correspondingly, the gas transmission coefficient of the compressor will also decrease, and the refrigeration capacity will decrease. When the cooling capacity is less than the heat load of the warehouse, the temperature of the warehouse will drop slowly. The refrigeration capacity of the compressor can be roughly judged by observing the suction and discharge pressures of the compressor. If the refrigeration capacity of the compressor decreases, the common method is to replace the cylinder liner and piston ring of the compressor. If it still fails to work after replacement, other factors should be considered, and even the machine should be disassembled for maintenance and troubleshooting.