Shanghai SANYO ultra-low temperature refrigerator repair [medical equipment repair]

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Case description: The refrigerator sent for repair is an ultra-low temperature refrigerator made in the United States. It adopts a refrigeration system with a check-type structure. Due to improper lubricating oil, the low-temperature compressor of the refrigerator held its shaft and the ultra-low temperature refrigerator gave a red alarm. The light is flashing. In this case, what we need to master is the experience and method of maintenance of ultra-low temperature refrigerator.
Analysis and maintenance: A US-made ℃ ultra-low temperature refrigerator used in a hospital. The red alarm light flashes minutes after starting.
After inspection, it was determined that the compressor in the low temperature section was holding the shaft. Since there was no r compressor on the market, I decided to dismantle the compressor and repair it myself. After draining the refrigerant, remove the compressor and pour out the refrigeration oil in the compressor. The color of the refrigeration oil has turned black-red. Use a lathe to drive away from the weld along the compressor, and first clean the part holding the shaft with kerosene. Then add lubricating oil. Restore the compressor, use the strong start method to run the compressor for about an hour, and then pour out the lubricating oil. Use argon arc welding to weld the compressor. Then use kerosene to clean the inside of the compressor. And turn the compressor upside down for an hour, add ordinary refrigeration oil, and start the compressor after connecting it to the system. Refrigeration starts normally until the low temperature box is working at around ℃. The red alarm light flashes again.
After inviting a refrigeration expert for consultation, I learned that after the compressor is repaired, "Tesi" brand precision instrument lubricating oil should be added. Because the temperature of ordinary lubricating oil is below ℃. The viscosity will increase and it is easy to block the outlet of the capillary tube. The pipe cooling stops, causing the equipment to alarm.
Update: Turn the compressor upside down for an hour, add precision instrument lubricating oil, and use the strong start method. Let the compressor run for hours. Then pour out the oil and add new precision lubricating oil. Start the compressor to fully evaporate the water inside. Then put it into the cryogenic box and evacuate it according to the routine, and fill it with cold water. The refrigeration performance of the test machine is restored when the power is turned on.