1. The refrigerator has poor heat insulation or sealing performance, resulting in a large loss of cooling capacity. The poor thermal insulation performance of cold storage is due to the insufficient insulation thickness of pipes and insulation walls, 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, the thermal insulation and moisture-proof properties of thermal insulation materials may be destroyed, resulting in moisture, deformation and even erosion of the thermal insulation layer, which reduces its thermal insulation capacity, increases heat loss and obviously slows down the temperature drop of the warehouse. 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 there is dew on the sealing strip or insulation wall of the warehouse door, it means that the seal is not tight. In addition, frequent opening and closing of the warehouse door or multiple 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 inventory is frequent or too large, the heat load increases sharply, and it usually takes a long time to cool down to the specified temperature.
2. The frost on the evaporator surface of the freezer is too thick or there is 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 too much dust on the surface of evaporator. Because the surface temperature of the evaporator in the cold storage is mostly below 0℃, the humidity in the warehouse is high, and the moisture in the air is easy to frost or even freeze on the evaporator surface, which affects the heat transfer effect of the evaporator. In order to prevent the frost layer on the evaporator surface from being too thick, it is necessary to defrost regularly. Here are two simple defrosting methods: ① Stop the machine and 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 Frost. After the goods in the warehouse are moved out, the surface of the evaporator tube is directly washed with high-temperature tap water to dissolve or fall off the frost layer. In addition to frosting too thick, the heat transfer effect of evaporator will be poor, and the heat transfer efficiency of evaporator will be obviously reduced because of long-term cleaning too thick.
3. The evaporator (air cooler) area of the freezer is not enough.
4. There is more air or frozen oil in the evaporator of the freezer, which reduces the heat transfer effect. Once more refrigeration oil adheres to the inner surface of the heat transfer tube, the heat transfer coefficient of the evaporator will decrease. Similarly, if there is more air in the heat transfer tube, the heat transfer area of the evaporator will be reduced, its heat transfer efficiency will be obviously reduced, and the temperature drop speed of the warehouse will be slowed down. Therefore, in the daily operation and maintenance, attention should be paid to remove the oil stain on the inner surface of the evaporator heat transfer tube in time, exhaust the air in the evaporator and improve the heat transfer efficiency of the evaporator.
5. Improper adjustment or blockage of the throttle valve of the freezer, too large or too small refrigerant flow and improper adjustment or blockage of the throttle valve of the freezer will directly affect the refrigerant flow entering the evaporator. If the throttle valve is too large, the refrigerant flow will be too large, the evaporation pressure and temperature will also rise, and the temperature drop speed of the freezer 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 speed will also slow down. Generally, the refrigerant flow 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 reasons for throttle blockage are ice blockage and dirty blockage. The ice jam is because the drying effect of the dryer is not good and the refrigerant contains water. When it flows through the throttle valve, the temperature drops below 0℃, and the water in the refrigerant forms ice, blocking the throttle valve hole. Dirty blockage is due to the accumulation of more dirt on the filter screen at the entrance of the throttle valve, which is caused by poor refrigerant circulation.
6. The quantity of refrigerant in the refrigeration system is insufficient, and the refrigeration capacity is insufficient. There are two main reasons for insufficient refrigerant circulation in cold storage. First, the refrigerant charge is insufficient. At this time, it is only necessary to replenish enough refrigerant. Another reason is that there is a large amount of refrigerant leaking in the system. In this case, we must first find the leakage point, focus on checking the joints of various pipelines and valves, find out the leakage part and repair it before filling enough refrigerant.
7. The compressor is inefficient, and the refrigeration capacity can't meet the warehouse load requirements. Due to the long-term operation of the compressor, the cylinder liner and piston ring are seriously worn, and the fitting clearance increases, so the sealing performance will be correspondingly reduced, the gas transmission coefficient of the compressor will also be reduced, and the refrigeration capacity will also be reduced. When the cooling capacity is less than the heat load of the warehouse, the temperature of the warehouse will drop slowly. By observing the suction and discharge pressures of the compressor, the refrigeration capacity of the compressor can be roughly judged. 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 doesn't work after replacement, other factors should be considered, and even the machine should be disassembled for maintenance and troubleshooting.
It's best to call the manufacturer and ask the maintenance master to come and repair it. -Foshan Skoman, be the freezer that knows you best.