Compressor always overheating protection, why is it?
Jun 25 , 2024

Compressor overheating protection is to protect the compressor motor is not burned, when the motor temperature or the compressor's own temperature exceeds a certain value, through the built-in or external some of the protection device to disconnect the compressor's working power, so as to achieve the role of protecting the compressor.

Refrigeration compressor from the system to absorb low temperature and low pressure gaseous refrigerant directly into the compressor shell cavity, the inhaled refrigerant first cooling the motor, and then pressure Therefore, the size of the inhaled refrigerant vapor superheat, is the compressor is overheated or not an important reason. Shrinking.

Discharge temperature overheating is mainly due to the following reasons: high return gas temperature, motor heating, high compression ratio, high condensing pressure, improper refrigerant selection.

1. High return gas temperature

The return temperature is relative to the evaporation temperature. In order to prevent the return of liquid, the general return gas pipeline requires 20 ° C return gas superheat. If the return air pipeline insulation is not good, the degree of superheat is far more than 20 ° C. The higher the return gas temperature, the higher the cylinder suction temperature and exhaust temperature. For every 1°C increase in return gas temperature, the exhaust gas temperature will increase by 1 to 1.3°C.

2. Motor Heating

For return air cooled compressors, refrigerant vapor is heated by the motor as it flows through the motor chamber, and the cylinder suction temperature is raised again. Motor heating by the power and efficiency, and power consumption and displacement, volumetric efficiency, working conditions, frictional resistance, etc. are closely related.

For return air-cooled semi-hermetic compressors, the temperature rise of the refrigerant in the motor chamber ranges roughly between 15 and 45°C. Air-cooled (air-cooled) type compressor in the refrigeration system does not pass through the winding, so there is no motor heating problem.

3. High compression ratio

Exhaust temperature is greatly affected by the compression ratio, the greater the compression ratio, the higher the exhaust temperature. Reduce the compression ratio can significantly reduce the exhaust temperature, the specific methods include improving suction pressure and reduce exhaust pressure.

Suction pressure is determined by evaporating pressure and suction line resistance. Improve the evaporating temperature, can effectively improve the suction pressure, quickly reduce the compression ratio, thereby reducing the exhaust temperature.

Some users think that the lower the evaporation temperature, the faster the speed of coldness, this idea actually has many problems. Although lower evaporating temperature can increase the freezing temperature difference, but the compressor cooling capacity is reduced, so the freezing speed is not necessarily fast. Not to mention that the lower the evaporating temperature, the lower the refrigeration coefficient, while the load has increased, the operating time is extended, the power consumption will increase.

Reduce the return air line resistance can also improve the return pressure, specific methods include timely replacement of dirty plugged return air filter, as far as possible to reduce the length of the evaporator tube and the return air line and so on.

In addition, insufficient refrigerant is also a factor of low suction pressure. Refrigerant leakage should be timely replenished. Practice shows that it is simpler and more effective than other methods to reduce the exhaust temperature by increasing the suction pressure.

The main reason for high exhaust pressure is that the condensing pressure is too high. Insufficient condenser cooling area, scale accumulation, insufficient cooling air or water volume, too high cooling water or air temperature, etc. can all lead to too high condensing pressure. It is very important to select the proper condensing area and maintain adequate cooling media flow.

High temperature and air conditioning compressor designed to run a low compression ratio, used for freezing after the compression ratio increased exponentially, the exhaust temperature is very high, and cooling can not keep up, resulting in overheating due to the avoidance of over the range of use of the compressor, and make the compressor work in the smallest possible pressure ratio. In some low-temperature systems, overheating is the primary cause of compressor failure.

4. Counter-expansion and gas mixing

After the start of the suction stroke, the high-pressure gas trapped in the cylinder gap will have a counter-expansion process. After the counter-expansion of the gas pressure back to the suction pressure, for the compression of this part of the gas and the energy consumed in the counter-expansion of the loss. The smaller the clearance, the smaller the power consumption caused by the counter-expansion on the one hand, and the larger the suction volume on the other hand, the compressor's energy efficiency ratio is therefore greatly increased.


During the counter-expansion process, the gas absorbs heat in contact with the high temperature surfaces of the valve plate, the top of the piston and the top of the cylinder, so that the temperature of the gas at the end of the counter-expansion does not drop to the suction temperature.

After the counter-expansion is finished, the real suction process starts. Gas into the cylinder on the one hand and the counter-expansion gas mixing, temperature increase; on the other hand, the mixed gas from the wall heat absorption and warming.

Therefore the gas temperature at the beginning of the compression process is higher than the suction temperature. However, due to the anti-expansion process and suction process is very short, the actual temperature rise is very limited, generally less than 5'.

The counter-expansion is caused by the cylinder clearance, which is a disadvantage that cannot be avoided in conventional piston compressors. The valve plate exhaust hole in the gas can not be discharged, there will be counter-expansion.

5. Compression temperature rise and refrigerant type

Different refrigerants have different thermophysical properties, the same compression process after the exhaust temperature rise is different. Therefore, for different refrigeration temperatures, different refrigerants should be used.

Conclusions and recommendations

Compressors should not overheat with high motor temperatures and excessive vapor discharge temperatures, etc., during normal operation within the operating range. Overheating of the compressor is an important fault signal, indicating a serious problem in the refrigeration system or improper use and maintenance of the compressor.

If the root cause of compressor overheating is the refrigeration system, only from the improvement of refrigeration system design and maintenance to solve the problem. Replacing the compressor with a new one will not eliminate the overheating problem at its root.

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