5 common causes of refrigeration system failures and solutions

5 common causes of refrigeration system failures and solutions

1. The suction temperature is too high-mainly caused by the increase of suction superheat. Note that high suction temperature does not mean high suction pressure, 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 temperature are: 　

　　(1) The refrigerant charge in the system is insufficient. Even if the expansion valve is opened to z*, the liquid supply will not change. In this way, the refrigerant vapor will overheat in the evaporator and the suction temperature will increase.

　　 (2) The opening of the expansion valve is too small, resulting in insufficient refrigerant circulation in the system, less refrigerant entering the evaporator, high superheat, and high suction temperature.　

　　(3) The expansion valve port filter is blocked, the liquid supply 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, such as poor insulation of the return air pipe or the pipe being too long, which can cause the suction temperature to be too high.

　　2. The suction air 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, which occupies part of the volume in the condenser and increases 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.　

　　 (2) 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 insulating material and its wrapping position is wrong, etc., which causes the temperature measured by the temperature sensing element to be inaccurate and close to the ambient temperature, causing the expansion valve to operate. The opening degree increases, resulting in excessive liquid supply.　

PS: Compressor is frosting-Reason 1: As above; Reason 2: Insufficient refrigerant charge, it will condense from the evaporator to the compressor (Note: need to be verified); Reason 3: The refrigerant is in the evaporator due to external reasons Insufficient evaporation or even non-evaporation will cause severe frosting and even wet compression. (If the return air of the central air conditioner is insufficient or the filter of the air conditioning box is seriously blocked, the return pipe of the compressor of the chiller will be frosted and the exhaust temperature will be very low) 　

　　3, the exhaust temperature is abnormal-influencing factors: adiabatic index, compression ratio, suction temperature　

　　The 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, and the discharge temperature is higher after the refrigerant vapor is compressed.　

　　 (2) When the condensing temperature rises, the condensing pressure is also higher, 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 the 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 transfer, 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-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. Increase in power consumption. If the exhaust temperature is too high, it will increase the consumption of compressor lubricating oil, make the oil thin, 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.　

　　 High exhaust pressure will increase the compression work and reduce the air delivery coefficient, which will reduce the refrigeration efficiency.　

　　The main reason for this failure:　

　　 (1) The flow of cooling water (or air) 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 occupies the effective condensation area; 　

　　 (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-mainly caused by low refrigerant flow or even stoppage in the refrigeration system pipeline.　

　　 Exhaust pressure is too low. Although the phenomenon is manifested on the high pressure side, the reasons are 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 discharge pressure.