Analyze the causes and countermeasures of compressor overheating protection

The compressor overheat protection mechanism is designed to prevent the compressor motor from burning out due to overheating. When the temperature of the motor or the temperature of the compressor itself exceeds a specific value, the working power of the compressor is cut off with the help of a built-in or external protection device to protect the compressor. In the refrigeration system, the refrigeration compressor draws low-temperature and low-pressure gaseous refrigerant from the system, and the refrigerant directly enters the shell cavity of the compressor. The sucked refrigerant first cools the motor and then is compressed. It can be seen that the degree of superheat of the inhaled refrigerant vapor is a key factor affecting whether the compressor overheats.

1. Insufficient refrigerant
When there is a shortage of refrigerant, the amount of refrigerant delivered to the evaporator will be reduced accordingly, causing the evaporation temperature to increase. As a result, the temperature of the refrigerant vapor sucked into the compressor will also increase, that is, the degree of superheat will increase, eventually causing the compressor motor coil to overheat, triggering the overheat protection.

In the hot summer, the ambient temperature is high. When the amount of refrigerant in the system is relatively small, it is difficult to judge whether the refrigerant is insufficient based solely on the current of the compressor and the pressure measured by the system. Instead, it is easy to overfill. At this time, it can be judged 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 increase. As the overall pressure of the system increases, the high pressure will naturally increase, which undoubtedly increases the burden on the compressor. In hot weather conditions, heat dissipation becomes difficult, and the current will increase, making the compressor prone to overheating protection.

The common manifestations are: the air blown by the outdoor unit fan is hotter than normal, the indoor unit condensation is relatively uniform, but the cooling effect is not as good as other equipment, the thin tube valve is not cold, and the thick tube valve has cold leakage. There may be no problem when used 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 exchanger are clean, some people only add fluorine based on the rated current or the so-called empirical current, resulting in too much fluoride.

3. The evaporator is dirty and blocked
If the evaporator's heat dissipation effect is extremely poor, it is like the internal fan not running. At this time, the evaporation effect of the refrigerant in the evaporator will be greatly reduced, and the compressor may inhale a gas-liquid mixed refrigerant. In this case, frost will appear on the return air from the compressor. Therefore, poor evaporator heat dissipation cannot simply be regarded as the cause of compressor overheating. However, when the heat dissipation effect of the evaporator is not ideal, it will lead to insufficient refrigerant intake by the compressor, that is, insufficient refrigerant circulation. This situation is entirely likely to trigger compressor overheating protection. Therefore, when repairing the compressor overheating protection fault, not only the condenser but also the evaporator needs to be cleaned.

4. The condenser is dirty and blocked
It is relatively easy to understand when the condenser is dirty and clogged. The condenser has poor heat dissipation and cannot take away heat in time, which will cause the system pressure to increase, thereby increasing the current, which will trigger overheating protection over time.

5. Four-way valve cross-gas
The compressor relies on low-temperature return air for cooling. If there is air crossflow in the four-way valve, the compressor will not suck in cold air, but hot air. As a result, the compressor not only cannot be cooled, but will "add fuel to the fire", the temperature will further increase, and it is not surprising that thermal protection occurs. When cross-gas occurs in the compressor, the refrigeration effect will deteriorate and the high pressure cannot be raised. At this time, thermal protection usually does not occur.

6. Lack of oil

A lack of oil in the compressor can indeed cause thermal protection. Lack of oil will cause poor lubrication of mechanical parts. This problem has been analyzed in detail by the "Refrigeration Encyclopedia" official account before.

7. Capacitor failure
It is not uncommon for problems with the capacitor to cause thermal protection of the compressor. Sometimes, the quality of capacitors purchased from the market is unreliable, and such problems are prone to occur.

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