Reasons for common failures of refrigeration system (1) Apr 13, 2021
1. Liquid back
For refrigeration systems that use expansion valves, liquid return is closely related to the improper selection and use of expansion valves. Excessive selection of the expansion valve, too small superheat setting, incorrect installation of the temperature sensing bulb, damaged adiabatic dressing, and failure of the expansion valve may cause liquid backflow.
For a small refrigeration system that uses capillary tubes, too much liquid will cause liquid back. When the evaporator is severely frosted or the fan fails, the heat transfer becomes poor, and the unevaporated liquid will cause liquid back. Frequent temperature fluctuations can also cause the expansion valve to fail to respond and cause liquid flood back.

For refrigeration systems where liquid back is difficult to avoid, installing a gas-liquid separator control can effectively prevent or reduce the hazards of liquid back.

2. Start with liquid
The phenomenon of violent foaming of the lubricating oil in the compressor is called liquid start. The bubbling phenomenon when starting with liquid can be clearly observed on the oil sight glass. The root cause is that a large amount of refrigerant dissolved in the lubricating oil and sinking under the lubricating oil suddenly boils when the pressure drops suddenly and causes the lubricating oil to bubble, which is easy to cause liquid hammer.

The installation of a crankcase heater (electric heater) in the compressor can effectively prevent the migration of refrigerant. Shut down for a short time and maintain the crankcase heater energized. After a long period of unused shutdown, heat the lubricating oil for several or ten hours before starting. Installing a gas-liquid separator on the return gas pipeline can increase the resistance of refrigerant migration and reduce the amount of migration.

3.Oil return
When the compressor is higher than the evaporator, the oil return bend on the vertical return pipe is necessary. The return bend should be as compact as possible to reduce oil storage. The spacing between the oil return bends should be appropriate. When the number of oil return bends is relatively large, some lubricating oil should be added.
Frequent starting of the compressor is not conducive to oil return. Since the compressor stops for a short continuous operation time, there is no time to form a stable high-speed air flow in the return pipe, and the lubricating oil can only stay in the pipe. If the oil return is less than Ben oil, the compressor will be short of oil. The shorter the operating time, the longer the pipeline and the more complex the system, the more prominent the oil return problem.
Lack of oil will cause serious lack of lubrication. The root cause of the lack of oil is not the amount and speed of the compressor, but the poor oil return of the system. The installation of an oil separator can quickly return oil and extend the compressor running time without oil return.

4.Evaporation temperature
The heating temperature has a great influence on the refrigeration efficiency. When it decreases by 1 degree, it needs to increase the power by 4% to produce the same cooling capacity. Therefore, when conditions permit, appropriately increasing the evaporation temperature is beneficial to improving the refrigeration efficiency of the air conditioner.
The evaporating temperature of Cold storage evaporator is generally 5 to 10 degrees lower than the air outlet temperature of the air conditioner.

Blindly lowering the evaporating temperature can cool the temperature difference, but the cooling capacity of the compressor is reduced, so the cooling 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.

5. Exhaust temperature is too high
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.

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