The overheat protection mechanism of the compressor aims to prevent damage to the compressor motor due to high temperature. When the temperature of the motor or compressor itself exceeds the safe range, the built-in or external protective device will automatically cut off the power to ensure the safety of the equipment. During the operation of the refrigeration compressor, low-temperature and low-pressure gaseous refrigerant is first extracted from the system and introduced into the compressor housing. During this process, the inhaled refrigerant will initially cool the motor before flowing through the motor chamber, and then be compressed. Therefore, the degree of superheat of the refrigerant vapor sucked in (i.e. the degree to which its temperature exceeds the saturation temperature) is one of the key factors determining whether the compressor will overheat.
1, Insufficient refrigerant
When the amount of refrigerant in the system is insufficient, the amount of refrigerant received by the evaporator decreases, resulting in an increase in evaporation temperature, which in turn causes an increase in the temperature of the refrigerant vapor sucked in by the compressor, known as an increase in superheat. This will directly cause the temperature of the compressor motor coil to rise, ultimately triggering the overheat protection mechanism. Especially in high temperature environments during summer, even if the refrigerant shortage in the system is not significant, it is difficult to accurately determine through conventional current or pressure detection, and it is prone to overfilling. At this point, evaluation can be conducted by measuring the temperature of the compressor exhaust pipe; Under normal circumstances, this temperature should be about 20 ℃ higher than the corresponding saturation temperature. If the actual measured value is lower than this standard, it indicates that there is too much refrigerant; On the contrary, if it exceeds this standard, it means that there is insufficient refrigerant. Similarly, the temperature of the suction pipe can also be used as a reference, usually it should be about 7 ℃ higher than the saturation temperature. If it deviates significantly from this value, it may indicate a problem of insufficient refrigerant.
2, Excessive refrigerant
When there is too much refrigerant in the system, the evaporation pressure and temperature will increase accordingly, thereby increasing the pressure burden on the entire system. Especially in hot weather conditions, heat dissipation becomes more difficult, accompanied by a larger operating current. These factors work together to easily cause the compressor to overheat and trigger the protection mechanism. Specific manifestations include but are not limited to: the outdoor unit fan emits abnormally hot air, although the indoor unit has uniform surface condensation, it does not feel cool enough, and the thin tube valve is not cold while the thick tube valve has a noticeable cold feeling. It is worth noting that some maintenance personnel may adjust the amount of refrigerant based on the current, but this may lead to misjudgment and ultimately result in the problem of excessive addition.
3, Evaporator and condenser are dirty
If the heat dissipation performance of the evaporator is poor, similar to the state where the internal fan stops running, the evaporation efficiency of the refrigerant in the evaporator will be greatly reduced, resulting in the compressor sucking in refrigerant in a gas-liquid mixture state, which usually leads to frost formation in the return air pipeline. However, when the evaporator is only slightly obstructed, although no obvious frosting phenomenon will immediately form, it is enough to affect the amount of refrigerant entering the compressor, thereby affecting the overall cycle efficiency, and ultimately may also cause overheating protection. Therefore, when dealing with such faults, it is recommended to clean both the evaporator and condenser simultaneously. For the condenser, once its heat dissipation effect deteriorates and it cannot effectively remove heat, it will lead to an increase in system pressure, followed by an increase in current, which may activate the overheat protection function after long-term operation.
4, Capillary or system blockage
Minor blockages in the capillary section are similar to extending the length of the capillary, leading to an enhanced throttling effect and further increase in pressure on the high-pressure side while relatively decreasing on the low-pressure side. In this case, the abnormal increase in air temperature discharged by the outdoor unit fan indicates that the pressure on the high-pressure side is too high. In addition, the evaporator may experience partial or complete non condensation due to low evaporation pressure. There has been a case where an air conditioning unit was installed improperly (such as in a narrow space of a high-rise building), coupled with an unreasonable design of the surrounding environment (such as the downward angle of the louvers restricting air circulation), causing the originally used air duct for heat dissipation to become a hot air return channel, resulting in frequent triggering of overheating protection. After on-site inspection and communication with the user, obstacles were removed and ventilation conditions were optimized, and the problem was resolved.
5, Voltage instability
When the power supply voltage drops below 190 volts, the compressor will exhibit a "blow by" phenomenon, that is, the volume of refrigerant gas sucked in expands, increasing the degree of superheat of the return gas, making it easy to trigger overheating protection. In a specific example, multiple air conditioning units in a certain area experienced similar malfunctions. Although the initial measurement showed a voltage of 210 volts, which seemed normal, the voltage quickly dropped below 190 volts after turning on other electrical devices. This not only prevented the air conditioning units from starting properly, but also posed a potential risk of damage to the compressor.
6, Four way valve for air leakage
The function of a four-way valve is to change the direction of refrigerant flow in heating mode, but if there is a leak, the compressor will suck in higher temperature gas instead of the expected low-temperature gas, which not only loses the expected cooling effect, but also exacerbates the heating process and increases the risk of overheating. In this case, the high-pressure side pressure of the compressor cannot reach the set value, so overheating protection will not be triggered.
7, Lack of oil
Sufficient lubricating oil is required inside the compressor to ensure lubrication between the moving parts. Lack of lubricating oil can increase friction, generate additional heat, and ultimately activate the overheat protection mechanism. We have provided a detailed introduction to this issue and its solutions in our previous articles.
8, Capacitor malfunction
The quality of compressor capacitors directly affects the starting and operating status of the motor. Poor quality or damaged capacitors may cause the motor to not obtain sufficient starting torque or a decrease in power factor during operation, both of which may lead to excessive current and trigger overheating protection. There are some unreliable products in the market, so caution should be exercised when choosing.
In summary, compressor overheating protection is a complex issue that involves multiple factors, ranging from external environmental factors to internal mechanical conditions, which may be contributing factors. Taking appropriate measures for different situations can effectively prevent and solve such problems.
