Analyzing the causes and countermeasures of compressor overheating protection

The compressor overheat protection mechanism aims to prevent the compressor  motor from burning out due to overheating. When the temperature of the motor or the compressor  itself exceeds a specific value, the working power of the compressor  is cut off with the help of internal or external protective devices to achieve protection of the compressor . In the refrigeration system, the refrigeration compressor  draws low-temperature and low-pressure gaseous refrigerant from the system, which directly enters the compressor's shell cavity. The inhaled refrigerant first cools the motor and is then compressed. From this, it can be seen that the degree of superheat of the refrigerant vapor sucked in is a key factor affecting whether the compressor  experiences overheating.

1, Insufficient refrigerant
When there is a shortage of refrigerant, the amount of refrigerant delivered to the evaporator will correspondingly decrease, leading to an increase in evaporation temperature. In this way, the temperature of the refrigerant vapor sucked in by the compressor will also increase, that is, the degree of superheat will increase, ultimately causing the compressor  motor coil to overheat and trigger overheating protection.
In the hot summer, when the ambient temperature is high and the lack of refrigerant in the system is relatively small, it is difficult to judge whether the refrigerant is insufficient solely based on the current of the compressor  and the pressure measured by the system. Instead, it is easy to overfill. At this point, judgment can be made by measuring the temperature of the compressor  exhaust pipe

2, Excessive refrigerant
When too much refrigerant is added, the evaporation pressure will increase and the evaporation temperature will also rise accordingly. Due to the overall increase in system pressure, the high pressure will naturally rise, which undoubtedly increases the burden on the compressor . In hot weather conditions, heat dissipation becomes difficult, and the current also increases, making the compressor  prone to overheating protection.
Its common manifestations are: the air blown out by the outdoor unit fan is hotter than normal, although the condensation in the indoor unit is more uniform, the cooling effect is not as good as other equipment, the thin tube valve is not cold, and the thick tube valve has a phenomenon of cold leakage. There may be no problem using it in the morning and evening, but overheating protection is prone to occur at noon. Moreover, when the voltage is normal and the filter and external heat exchange are clean, some people only add fluorine based on the rated current or so-called empirical current, resulting in an increase in fluorine.
3, Evaporator is dirty and blocked
If the heat dissipation effect of the evaporator is extremely poor, it is like an internal fan not running. At this point, the evaporation effect of the refrigerant in the evaporator will be greatly reduced, and the refrigerant sucked in by the compressor may be a mixture of gas and liquid. In this case, frosting may occur in the return air of the compressor . Therefore, the poor heat dissipation of the evaporator cannot be simply regarded as the cause of compressor overheating. However, when the heat dissipation effect of the evaporator is not ideal, it can lead to insufficient refrigerant intake by the compressor , that is, insufficient refrigerant circulation, which may completely trigger compressor  overheating protection. So, when repairing compressor overheating protection faults, not only should the condenser be cleaned, but also the evaporator needs to be cleaned.
4, The condenser is dirty and blocked
The situation of dirty and blocked condenser is relatively easy to understand. Poor heat dissipation of the condenser prevents timely removal of heat, which can lead to an increase in system pressure and current, eventually triggering overheating protection.

5, Capillary or system blockage
The occurrence of micro blockage in capillaries is similar to an increase in capillary length, which can lead to excessive throttling, an increase in high pressure, and a decrease in low pressure. At this point, the air blown out by the external fan will be very hot, which alone is enough to prove that the high pressure is too high. Incomplete condensation on the evaporator is a specific manifestation of low evaporation pressure. The common symptoms are: poor cooling effect, incomplete condensation on the evaporator, and hot air blown out by external heat exchange. Originally, the machine could barely run, but after adding refrigerant, the compressor even stopped working completely. When the refrigerant is discharged to the same state as other equipment, the condensation situation of the evaporator will be even worse, and the coarse pipe valve will show almost no signs of cooling.
6, Voltage too low
Practice has shown that when the power supply voltage drops below 190V, the system pressure will experience situations where high voltage cannot rise and low voltage cannot fall. This is equivalent to the phenomenon of gas leakage in the compressor , resulting in an increase in the specific volume of refrigerant gas sucked in by the compressor , which in turn causes an increase in the degree of superheat of the compressor return gas, ultimately triggering overheating protection.
7, Four way valve for air leakage
The compressor  relies on low-temperature return air for cooling. If there is air leakage in the four-way valve, then the compressor  is not sucking in cold air, but hot air. In this way, the compressor  not only fails to receive cooling, but also adds fuel to the fire, further increasing the temperature, and it is not surprising that thermal protection occurs. When there is air leakage in the compressor , the cooling effect will deteriorate and the high pressure cannot be increased. At this time, thermal protection usually does not occur.
8, Lack of oil
compressor  oil shortage can indeed lead to thermal protection. Lack of oil can cause poor lubrication of mechanical components, and this issue has been analyzed in detail by the "Refrigeration Encyclopedia" public account before.
9, Capacitor malfunction
It is not uncommon for problems with capacitors to cause thermal protection in compressor s. Sometimes, when the quality of capacitors purchased from the market is unreliable, such problems are prone to occur.

Shanghai KUB Refrigeration Equipment Co., Ltd.

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