What causes absorption?
A compressor’s lubricant should be miscible with the system refrigerant. Miscibility ensures that the lubricant sent into the refrigeration system from the compressor is reliably returned it, because the lubricant is physically combined with the refrigerant. At any normal temperature, the vapor pressure of the oil in a refrigeration system is much lower than the vapor pressure of the refrigerant, and during shut down periods, as a result of the miscibility of refrigerant in oil, refrigerant in contact with the surface of an oil pool is absorbed into the oil. This reduces the system pressure at the surface of the oil pool, causing diffusion of refrigerant vapor from refrigerant-rich zones in the system. This is the same effect that occurs when we open the bathroom door after taking a hot shower and humidity from the bathroom very quickly diffuses throughout our house. In the refrigeration system, though, absorption occurs even when all parts of the system are at the same temperature. As
