Causes and solutions for common failures of cold storage systems

1.The suction temperature is too high
The suction temperature is too high-mainly caused by the increase in the degree of superheat of the suction. Note that the high suction temperature does not mean that the suction pressure is high, because the suction is superheated steam.　Under normal circumstances, the compressor cylinder head should be half cold and half hot. If the suction temperature is too high, all the cylinder head will heat up. If the suction temperature is higher than the normal value, the exhaust temperature will rise accordingly.　
The main reasons for the excessively high suction temperature are:
(1) Insufficient refrigerant charge in the system. Even if the expansion valve is opened to the maximum, there will be no change in the liquid supply, so that the refrigerant vapor in the evaporator overheats and the suction temperature rises.
(2) The opening of the expansion valve is too small. As a result, the circulation of refrigerant in the system is insufficient, the amount of refrigerant entering the evaporator is small, the degree of superheat is large, and the suction temperature is high.　
(3) The filter screen of the expansion valve port is blocked. The supply of liquid in the evaporator is insufficient, the amount of refrigerant liquid is reduced, and a part of the evaporator is occupied by superheated steam, so the suction temperature increases.
(4) The suction temperature is too high due to other reasons. If the return air pipe is not well insulated or the pipe is too long, it can cause excessively high suction temperature.
2.The temperature is too low
The suction temperature is too low-mainly caused by the large liquid supply of the evaporator and the low suction superheat. (1) The refrigerant charge is too much. Occupies part of the volume in the condenser to increase the condensing pressure, and the liquid entering the evaporator increases accordingly. The liquid in the evaporator cannot be completely vaporized, so that the gas sucked by the compressor contains liquid droplets. In this way, the temperature of the return air duct drops, but the evaporation temperature does not change because the pressure does not drop, and the degree of superheat decreases. Even if the expansion valve is closed, there is no significant improvement.　
The opening of the expansion valve is too large. The temperature sensing element is too loosely bound, the contact area with the air return pipe is small, or the temperature sensing element is not wrapped with insulation material and its wrapping position is wrong, etc., resulting in inaccurate temperature measurement of the temperature sensing element, close to the ambient temperature, causing the expansion valve to operate The opening degree increases, resulting in excessive liquid supply.

Reasons for the frosting of the compressor: Reason 1: As above Reason 2: The refrigerant charge is insufficient, and it will condense from the evaporator to the compressor; Reason 3: Due to external reasons, the refrigerant will not evaporate in the evaporator or even not evaporate. Severe frost, and even wet compression.
3.The exhaust temperature is abnormal Abnormal
 discharge temperature-influencing factors: adiabatic index, compression ratio, suction temperature, and compressor discharge temperature can be read from the thermometer on the discharge pipe. It is related to the refrigerant's adiabatic index, compression ratio (condensing pressure/evaporating pressure) and suction temperature. The higher the suction temperature and the higher the compression ratio, the higher the exhaust temperature, and vice versa.　 When the suction pressure does not change, when the exhaust pressure increases, the exhaust temperature rises; if the exhaust pressure does not change, when the suction pressure drops, the exhaust temperature also rises. Both of these cases are caused by the increase in compression ratio. Too high condensation temperature and exhaust temperature are unfavorable to the operation of the compressor and should be prevented. Excessive exhaust temperature will cause the lubricating oil to become thinner or even carbonize and coke, thereby worsening the compressor lubrication conditions.　 The discharge temperature is proportional to the compression ratio (condensing pressure/evaporating pressure) and the suction temperature. If the superheat temperature of the suction is high and the compression ratio is large, the exhaust temperature is also high. If the suction pressure and temperature do not change, when the exhaust pressure increases, the exhaust temperature also increases.　 The main reasons for the increase in exhaust temperature are: 　(1) The suction temperature is higher. After the refrigerant vapor is compressed, the exhaust temperature is higher.　(2) Condensing temperature rises. The condensing pressure is also high, causing the exhaust temperature to rise.　(3) The exhaust valve plate is broken. The high-pressure steam is repeatedly compressed and the temperature rises, the cylinder and cylinder head are hot, and the indication value of the thermometer on the exhaust pipe also rises.　 The actual factors that affect the increase of exhaust temperature are: low intercooling efficiency, or excessive scale in the intercooler affects heat exchange, the suction temperature of the subsequent stage will inevitably be higher, and the exhaust temperature will also increase. The valve leaks and the piston ring leaks, which not only affects the increase in exhaust temperature, but also changes the pressure between stages. As long as the compression ratio is higher than the normal value, the exhaust temperature will rise. In addition, water-cooled machines, lack of water or insufficient water will increase the exhaust temperature. The condensing pressure is abnormal and the exhaust pressure is reduced.　
4.Higher exhaust pressure
High discharge pressure-mainly caused by high condensing pressure, not the compressor itself.　Exhaust pressure generally corresponds to the condensation temperature. Under normal circumstances, the discharge pressure of the compressor is very close to the condensing pressure.　When the condensing pressure increases, the compressor discharge temperature also increases. The compression ratio of the compressor increases, and the air delivery coefficient decreases, so that the cooling capacity of the compressor decreases. Increased power consumption. If the exhaust temperature is too high, it will increase the consumption of compressor lubricating oil, make the oil thinner, and affect lubrication; when the exhaust temperature is close to the compressor oil flash point, part of the lubricating oil will also be carbonized and accumulated in the suction, The exhaust valve port affects the sealing performance of the valve.　 Reducing the temperature of the cooling medium can reduce the condensation temperature and the condensation pressure. However, this is limited by environmental conditions and is difficult to choose artificially. Increasing the flow of the cooling medium can lower the condensation temperature a little (this method is often used). However, the flow of cooling water or air cannot be increased one-sidedly, because this will increase the power of the cooling water pump or fan and motor, which should be considered comprehensively.　Higher exhaust pressure will increase the compression work and reduce the gas transmission coefficient, thus reducing the refrigeration efficiency.　 The main reasons for this failure are: 　(1) the cooling water (or air) flow is small and the temperature is high; 　(2) there is air in the system, which increases the condensing pressure; 　(3) the refrigerant charge is too much and the liquid is occupied The effective condensing area is improved; 　(4) The condenser is out of repair for a long time, and the heat transfer surface is seriously dirty, which can also cause the condensing pressure to rise. The presence of scale also has a greater impact on the condensation pressure.
5.Exhaust pressure is too low
 Exhaust pressure is too low-mainly caused by the low refrigerant flow in the refrigeration system pipeline or even stoppage.　 Exhaust pressure is too low, although its phenomenon is manifested in the high-pressure side, but the reason is mostly at the low-pressure side. The reason: the expansion valve is blocked by ice or dirty, and the filter is blocked, which will inevitably reduce the suction and exhaust pressure.