Reasons for Pump Body Failures in Cold Storage Compressors

During the operation of cold storage, certain problems are bound to be encountered.

These malfunctions can be either minor or major. The failures of the compressor pump body mainly occur in the scroll plates and bushings.

A scroll compressor has two scroll plates, namely the orbiting scroll and the fixed scroll. Together with the sealing materials, they form the compression chambers of the scroll compressor. Generally, scroll compressors used in air conditioners have a three-stage compression process, and the volume of the last-stage compression chamber is basically one-third of the inhaled gas. When a large amount of liquid enters the scroll plates, due to the incompressibility of the liquid state, under the effect of instantaneous high pressure, the scroll plates are bound to break.

Solid particles entering the compression chamber also pose a fatal threat to the scroll plates. The following mainly analyzes the reasons for their damage from several aspects:

When the compressor is started, a large amount of refrigerant liquid enters it. After the unit has been running and is left overnight, part of the refrigerant flows back to the bottom of the compressor, or if the refrigerant charge in the unit system originally exceeds the standard, liquid refrigerant will accumulate at the bottom of the compressor. At the moment when the compressor is started, the liquid refrigerant, along with the lubricating oil, rushes into the scroll plates, causing hydraulic impact and resulting in the breakage of the scroll plates. Generally, compressor manufacturers will recommend installing a preheating belt at the bottom of the compressor. Turn on the preheating belt 6 hours before starting the compressor to preheat the refrigerant at the bottom so that the bottom refrigerant can evaporate. However, in practice, this measure is not very practical.

During the defrosting process of the heat pump, the refrigerant does not fully evaporate before entering the compressor. When the air conditioner is operating in heating mode, the refrigerant flows into the compressor in a vapor state. At this time, the gas-liquid separator is in a low-pressure state, while the evaporation side is in a high-pressure state. After the machine receives the defrosting instruction, the four-way valve operates, and the evaporation side is connected to the gas-liquid separator. A large amount of liquid accumulates in the gas-liquid separator and then flows into the compressor, causing excessive liquid slugging. Therefore, in some air conditioning systems, a liquid level detection device is adopted. When the liquid level reaches a certain level, the system sends an instruction to stop defrosting. This protection device effectively prevents liquid slugging during defrosting.

Impurities and moisture enter the scroll plates of the compressor. The sources of impurities mainly include two major parts:

Bushing burnout
This failure mainly occurs in the bearing between the orbiting scroll and the main shaft. Due to insufficient refrigerant in the system or the reverse rotation of the compressor, which causes an abnormally high temperature in the center of the scroll, the bottom of the orbiting scroll heats up rapidly, resulting in the burnout of the bushing of the bearing. In addition, the abnormal high temperature of the motor can also lead to the burnout of the motor bushing and the burned bushing.

Bushing wear
Poor lubrication is the main cause of bushing wear. When the refrigerant in the system exceeds the standard, the compressor experiences excessive liquid return, the compressor starts frequently, foreign objects enter and cause the oil film to break or clog, or there is an abnormally high temperature in the bearing part, all of which can lead to poor lubrication. When moisture enters the system, it causes rust spots on the parts, resulting in wear. In severe cases, it can cause the shaft to seize up and the machine to stop working, and the bushings will be worn.