This is a common failure of refrigeration compressors!
Suction temperature is too high
The excessively high suction temperature is mainly caused by the increase of suction superheat. Note that high suction temperature does not mean high suction pressure, because 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 cylinder heads will heat up. If the suction temperature is higher than the normal value, the exhaust temperature will rise accordingly.
The main reasons for excessively high suction temperature:
1.The refrigerant charge in the system is insufficient. Even if the expansion valve is opened to the maximum, the liquid supply will not change, 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.Excessively high suction temperature caused by other reasons. If the return air pipe is not well insulated or the pipe is too long, it can cause excessively high suction temperature.
The suction 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.Too much refrigerant charge. 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.
2. The opening of the expansion valve is too large. Because the temperature sensing element is loosely bound, the contact area with the return pipe is small, or the temperature sensing element is not wrapped with insulating material and its wrapping position is wrong, the temperature measured by the temperature sensing element is inaccurate, close to the ambient temperature, and the expansion valve is activated. The opening degree increases, resulting in excessive liquid supply.
Reason: Insufficient refrigerant charge will flow from the evaporator to the compressor (note: verification is required). In addition, due to external reasons, the refrigerant does not evaporate in the evaporator or even does not evaporate. At this time, it will form severe frost and even cause 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)
The exhaust temperature is abnormal
Abnormal exhaust temperature-influencing factors: adiabatic index, compression ratio, suction temperature.
The compressor discharge temperature can be read from the thermometer on the discharge line. 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 is constant and the discharge pressure rises, the discharge temperature rises; if the discharge pressure remains the same, when the suction pressure drops, the discharge temperature also rises. The Refrigeration Encyclopedia public account will remind you of these two situations All are caused by the increase in compression ratio. Too high condensing temperature and exhaust temperature are harmful 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 superheating 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. The discharge temperature is higher after the refrigerant vapor is compressed.
2. The condensing temperature rises and the condensing pressure is also high, causing the exhaust temperature to rise.
2.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 indicating 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, the public account of Refrigeration Encyclopedia reminds you that 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.
Higher exhaust pressure
The exhaust pressure generally corresponds to the condensation temperature. Under normal circumstances, the discharge pressure of the compressor is very close to the condensing pressure. High exhaust pressure will increase the compression work and reduce the gas transmission coefficient, thereby reducing the refrigeration efficiency.
When the condensing pressure increases, the compressor discharge temperature also increases. The compression ratio of the compressor increases and the air delivery coefficient decreases, thereby reducing the cooling capacity of the compressor. Increase in power consumption. If the exhaust temperature is too high, it will increase the compressor lubricating oil consumption, 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.
The main reasons for this failure:
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 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
Exhaust pressure is too low-mainly caused by the low refrigerant flow in the refrigeration system pipeline or even stop.
Exhaust pressure is too low, although the phenomenon is manifested in the high-pressure side, but the reason is mostly at the low-pressure side. The reason may be that the expansion valve is blocked by ice or dirty, and the filter is blocked, which will inevitably reduce the suction and discharge pressure.
6
Insufficient exhaust
Insufficient air displacement-mainly compared with the compressor's design air volume, it is one of the most prone failures of the compressor. Its appearance is mainly caused by the following reasons:
1. The intake filter is clogged with fouling or the compressor suction pipe is too long and the pipe diameter is too small, which increases the suction resistance, affects the suction volume and reduces the discharge volume.
2. The reduction of compressor speed reduces the displacement. If the compressor is used in an improper environment, because the compressor's displacement is designed according to a certain altitude (this item is mainly an air compressor), suction temperature, humidity, and power supply, when it is used in excess of the above standards When the air compressor is used in the high original environment, the suction pressure will decrease, etc., and the discharge capacity will also be affected.
3. The packing is not tightly sealed to cause air leakage and reduce the exhaust volume. The reason is that the packing itself is not in compliance with the requirements when it is manufactured; secondly, it may be caused by abrasion and strain during installation, causing air leakage; generally, lubricating oil is added to the packing to provide lubrication, sealing, and cooling.
