Three common reasons for overcurrent protection of compressors

January 31, 2024

Three common reasons for overcurrent protection of compressors



Simply put, there are three reasons for compressor overcurrent:

The condensation pressure of the refrigeration system is too high;
Excessive refrigerant in the refrigeration system;
The compressor lacks refrigeration oil;

Let's analyze them separately below:

1、 Poor external heat dissipation

(1) Short circuit of external unit return and exhaust: If the external unit is installed in a closed balcony, narrow hallway, or in non ventilated areas such as the house, there are obstacles in front of the air outlet.

(2) The external unit has low air volume and slow heat dissipation speed: if the condenser of the external unit is too dirty or blocked by dust and oil, the fan motor speed is slow, the fan capacitance decreases, and the surrounding temperature of the external unit is high.

2、 External power supply voltage factor

Low or high power supply voltage can cause high operating current of the compressor, with the majority of cases occurring in China, especially during peak electricity usage.

(1) If the power supply voltage (i.e. the voltage before startup) is too low, the user should rewire it. If the voltage is around 190V, a voltage regulator can be considered for installation. If it is too low, it will be ineffective.

(2) Check the voltage drop after startup. Under normal circumstances, the voltage drop is only about ten volts. If the voltage drop is too large (it is recommended to have a voltage drop of more than 20V and the voltage after the compressor starts is 190V lower), the power cord should be thickened or rewired, and faults such as poor circuit contact should be ruled out.

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3、 Refrigeration system malfunction

(1) Air mixed into the refrigeration system: If there is air in the system, it often accumulates in the upper part of the condenser because it cannot pass through the condenser's accumulator. The presence of air in the system can generally be determined by the fluctuation of system pressure. If there is air in the system, it should be re evacuated and fluorinated.

(2) Excessive fluorine: The compressor is in an overloaded state for a long time, which will eventually cause the compressor to overcurrent and trip. In this situation, some fluorine should be released to the standard range (the suction pressure is about 0.5MPa when the ambient temperature is 35 degrees).

4、 High shell/internal temperature

(1) Poor lubrication of the compressor: If the height difference between indoor and outdoor units is greater than 5 meters, no oil return bend has been made, or only one oil return bend has been made on one pipe, the system cannot return oil smoothly. Due to the lack of lubrication, the temperature of the compressor slowly rises during operation, ultimately leading to overheating and tripping.

For example, when the outdoor unit is located below and heating is running, the gaseous working fluid flows upward in the coarse tube, and the liquid working fluid flows downward in the fine tube, resulting in poor oil return. The outdoor unit is on top, heating is running, and the gaseous working fluid flows downward in the coarse tube, while the liquid working fluid flows upward in the fine tube, so the oil return is better.

When cooling, the situation is opposite to the above. There are two types of oil return bends: U-shaped and S-shaped. The S-shaped bend can be added in the middle of the connecting pipe, and the U-shaped bend is generally close to the machine installation, and the radius should be as small as possible.

(2) Impurities and excessive moisture in the system can cause the lubricating oil to deteriorate, carbonize, and fail to function properly, resulting in a sharp increase in compressor temperature and overheating, causing the machine to trip.

This situation usually occurs on machines that have been repaired or have been used for a long time. If the substance in the system is black, it is certain that this situation exists. At this time, nitrogen should be used to clean the system, replace the compressor and capillary components, and evacuate and add fluorine again.

(3) Air conditioning is often used in environments below 0 degrees Celsius: When the compressor starts, the lubricating oil bubbles, causing a large amount of lubricating oil to flow out of the compressor instantly. At this time, even if the system is designed well, it is useless. The speed of oil return is much lower than the oil discharge speed, and the compressor lacks lubrication, causing temperature rise and overheating protection.

In this situation, an oil heater (40W --60W, 220V) should be installed on the compressor. When the compressor stops, continue to keep the oil heater energized. The connection method is to connect the oil heater in series with the normally closed switch of the contactor, and then connect it to the fire and zero lines of the power supply.

5、 Poor cooling effect of the compressor

The system has too little fluorine, and the temperature of the compressor is very high during operation. The high-temperature coil is cooled by the refrigerant sucked in. If there is too little fluorine, the system flow rate is small, which cannot meet the 100% load of the evaporator, resulting in an increase in suction superheat. In addition, the small suction flow rate of the compressor leads to a significant decrease in cooling efficiency. This long-term operation can lead to compressor thermal protection.





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