Abstract: Starting from the perspective of the solubility characteristics of refrigerants and oil, compares and studies the differences in oil surface changes during low-temperature heating start-up under different solubility characteristics conditions, and analyzes the changes in the solubility of refrigerants in oil during low-temperature heating start-up, and a solution for the low-temperature start characteristics of oil was proposed. During the low-temperature start-up process, oil with a slow increase in refrigerant solubility with temperature (insoluble oil) show a decrease of about 17% in refrigerant solubility. The time for the oil temperature to rise to stability is about 600 seconds, indicating a more stable oil level. Oil with a steep increase in refrigerant solubility with temperature (soluble oil) show a decrease of about 34% in refrigerant solubility during low-temperature start-up, and the time for oil temperature to rise to stability is about 300 seconds. Compared with slow rise oil, the solubility change is greater, the oil temperature rises faster, and the refrigerant quickly separates from the oil due to the decrease in solubility, resulting in a phenomenon similar to "flash evaporation". The oil is discharged from the compressor in large quantities with the refrigerant, it may even cause oil shortage on the compressor side. Based on the difference between rapidly increasing and slowly increasing refrigerant solubility oil, a solution for the phenomenon of oil shortage in rapidly increasing refrigerant solubility oil is proposed: reduce the rate of solubility change and the rate of oil temperature rise, thereby avoiding the refrigerant from evaporating and carrying oil away from the compressor.

Key words: Compressor, Low temperature heating start-up, Solubility, Insoluble oil, Soluble oil