Common problems of after-sales maintenance of condensing unit (2) Jun 23, 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.

Evaporation temperature/return air temperature/return air pressure.

1. Every time the evaporation temperature increases by 10℃, the motor load can increase by 30% or even higher, causing the phenomenon of small horse-drawn carts. Therefore, if the low-temperature compressor is used in the medium and high temperature system and the cold storage cooling process lasts too long, the compressor will be overloaded for a long time, which will cause great damage to the motor, causing the motor to encounter unexpected situations such as voltage fluctuations and surges in the future. It is easy to burn at times.
2. The lower the evaporation temperature, the smaller the refrigerant mass flow, and the smaller the actual motor power required. Therefore, when air-conditioning compressors and medium-high temperature refrigeration compressors are used at low temperatures, although the actual power consumption of the motor is much smaller than the nominal power, it is still too large compared to the actual power requirements and cooling conditions at low temperatures, and the motor cooling is easy problem appear.
3. The return air temperature is relative to the evaporation temperature. In order to prevent liquid return, the return gas pipeline generally requires a return gas superheat of 20°C. If the return air pipe is not well insulated, the superheat will far exceed 20°C.

4. The higher the return air temperature, the higher the cylinder suction temperature and exhaust temperature. Every time the return air temperature increases by 1°C, the exhaust temperature will increase by 1 to 1.3°C.

5. For the return air cooling compressor, the refrigerant vapor is heated by the motor when it flows through the motor cavity, and the cylinder suction temperature is once again increased. The calorific value of the motor is affected by power and efficiency, and the power consumption is closely related to displacement, volumetric efficiency, working conditions, friction resistance, etc.
6. Although lowering the evaporating temperature can increase the freezing temperature difference, the refrigeration capacity of the compressor is reduced, so the freezing speed is not necessarily fast. What's more, the lower the evaporation temperature, the lower the refrigeration coefficient, but the load increases, the operating time is prolonged, and the power consumption will increase.
7. Reducing the resistance of the return air pipeline can also increase the return air pressure. The specific methods include timely replacement of the dirty return air filter, and minimizing the length of the evaporation pipe and the return air pipeline as much as possible.
8. In addition, insufficient refrigerant is also a factor of low return pressure.

Return air temperature is too high
1. The refrigerant charge in the system is insufficient. Even if the expansion valve is opened to the maximum, the liquid supply will not change. In this way, the refrigerant vapor will overheat in the evaporator coil and the suction temperature will increase.
2. The opening of the expansion valve is too small, resulting in insufficient refrigerant circulation in the system. The amount of refrigerant entering the evaporator coil is small, the superheat is large, and the suction temperature is high.
3. The expansion valve port filter is blocked, the liquid supply in the evaporator coil is insufficient, the amount of refrigerant liquid is reduced, and a part of the evaporator is occupied by superheated steam, so the suction temperature rises.
4. The suction temperature is too high due to other reasons, such as poor heat insulation of the return air pipe or the pipe being too long, which can cause the suction temperature to be too high. Under normal circumstances, the compressor cylinder head should be half cold and half hot.

Return air temperature is too low
1. Too much refrigerant charge, occupying part of the condenser volume and increasing the condensing pressure, and the liquid entering the evaporator coil will increase accordingly. The liquid in the evaporator cannot be completely vaporized, so that the gas sucked by the compressor contains liquid droplets. In this way, the temperature of the return air duct decreases, but the evaporation temperature does not change because the pressure does not decrease, and the degree of superheat decreases. Even if the expansion valve is closed, there is no significant improvement.
2. The opening of the expansion valve is too large. Because the temperature sensing element is loosely bound, the contact area with the return pipe is small, or the temperature sensing element is not wrapped with insulating material and its wrapping position is wrong, etc., the temperature measured by the temperature sensing element is inaccurate and close to the ambient temperature, causing the expansion valve to operate. The opening degree increases, resulting in excessive liquid supply.
The influence of evaporating temperature on refrigeration efficiency
1. The evaporating temperature has a great influence on the refrigeration efficiency. When it decreases by 1 degree, the same cooling capacity needs to increase the power by 4%. Therefore, if conditions permit, appropriately increasing the evaporation temperature is beneficial to improving the cooling efficiency of the air conditioner. of. The evaporating temperature of household air conditioners is generally 5 to 10 degrees lower than the air outlet temperature of the air conditioner. In normal operation, the evaporating temperature is 5 to 12 degrees, and the outlet temperature is 10 to 20 degrees.

Air-cooled condensing unit manufacturerLarge condensing unitEmerson Condensing Unit

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