Common problems of after-sales maintenance of condensing unit (3) Jun 25, 2021

KITDOO COOLING is a company integrating design and production of refrigeration equipment. KITDOO can give you professional one-stop service for cold chain.

This issue mainly introduces the common problems of the after-sales maintenance of the condensing unit.

Exhaust temperature/exhaust pressure/exhaust volume
1. The main reasons for the excessively high exhaust temperature are as follows: high return air temperature, large heating capacity of the motor, high compression ratio, high condensation pressure, adiabatic index of the refrigerant, and improper refrigerant selection.
2. For the R22 compressor, when the evaporation temperature is reduced from -5°C to -40°C, the COP will generally be reduced by 4 times, and other parameters will not change much, and the temperature rise of the gas in the motor cavity will increase by three or four times. As the cylinder suction temperature increases by 1°C, the exhaust temperature can increase by 1 to 1.3°C. Therefore, when the evaporation temperature is reduced from -5°C to -40°C, the exhaust steam temperature will rise by about 30-40°C. In the return air cooling type semi-hermetic compressor, the temperature rise of the refrigerant in the motor cavity is roughly between 15 and 45°C.
3. In the air-cooled (air-cooled) compressor, the refrigeration system does not pass through the windings, so there is no motor heating problem.

4. The exhaust temperature is greatly affected by the compression ratio (condensing pressure/evaporating pressure, generally 4). Under normal circumstances, the discharge pressure of the compressor is very close to the condensing pressure. When the condensing pressure increases, the compressor discharge temperature also increases. The larger the compression ratio, the higher the exhaust temperature and the reduction of the air delivery coefficient, which reduces the cooling capacity of the compressor and increases the power consumption.
5. Reducing the compression ratio can significantly reduce the exhaust temperature. The specific methods include increasing the suction pressure and reducing the exhaust pressure. The suction pressure is determined by the evaporation pressure and the resistance of the suction pipe. Increasing the evaporation temperature can effectively increase the suction pressure and rapidly reduce the compression ratio, thereby reducing the exhaust temperature.
6. Practice shows that reducing the exhaust temperature by increasing the suction pressure is simpler and more effective than other methods.

7. The main reason for the high exhaust pressure is that the condensing pressure is too high (there is air in the system; the refrigerant charge is too much, the liquid occupies the effective condensing area; the condenser heat dissipation area is insufficient, fouling, cooling air volume or insufficient water volume , Cooling water or air temperature is too high, etc.). It is very important to choose a suitable condensing area and maintain sufficient cooling medium flow.
8. Exhaust pressure is too low. Although the phenomenon is manifested in the high-pressure side, the reasons are mostly at the low-pressure side.
9. Insufficient air displacement is mainly due to the fact that the compressor suction pipe is too long and the pipe diameter is too small compared with the compressor’s design air volume, which increases the suction resistance, affects the suction volume and reduces the discharge volume.

Condensing unit production site

Liquid strike
1. In order to ensure the safe operation of the compressor and prevent the occurrence of liquid hammer, the suction temperature is required to be higher than the evaporation temperature, that is, it should have a certain degree of superheat. The degree of superheat can be achieved by adjusting the opening degree of the expansion valve.
2. Avoid excessively high or low temperatures. If the suction temperature is too high, that is, the overheating is too high, which will cause the compressor discharge temperature to rise. If the suction temperature is too low, it indicates that the refrigerant is not completely evaporated in the evaporator, which not only reduces the heat exchange efficiency of the evaporator, but the suction of wet steam will also cause compressor liquid hammer. The suction temperature should be 5~10℃ higher than the evaporation temperature under normal circumstances.

Air cooler for cold storage
1. For the commonly used R22 refrigerant, the cooling capacity of the compressor decreases with the increase of effective superheat. When the superheat is 10℃, the cooling capacity is 99.5% of the cooling capacity under saturated evaporation, and when the superheat is 20 At ℃, the cooling capacity is 99.3% of the cooling capacity under saturated evaporation. It can be seen that the attenuation of the cooling capacity with the increase of superheat is very small.
2. The refrigerant maintains a certain degree of superheat, which can further prevent the liquid hammer phenomenon in the cylinder. For low-temperature refrigeration systems, appropriately increasing the effective superheat can make the lubricating oil return to the compressor more smoothly. But as the compressor suction superheat increases, its discharge temperature also rises. Excessive discharge temperature will make the lubricating oil viscosity thinner and even carbonize, affecting the normal operation of the compressor, so the suction superheat should be controlled. Within a certain range.

Add fluoride
1. When the amount of fluorine is small or its regulating pressure is low (or partially blocked), the valve cover (bellows) of the expansion valve and even the liquid inlet will be frosted; when the amount of fluorine is too small or there is basically no fluorine, the appearance of the expansion valve No response, only a faint sound of airflow can be heard.
2. See from which end the icing starts, whether it is from the dispensing head or from the return pipe of the compressor. If the dispensing head is lack of fluorine, the compressor is more fluorine.

Regarding the daily maintenance of the condensing unit, you can refer to the previous two blogs.

V-type condenser

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