A method for introducing a refrigerant and lubricant into a vapor-compression heat transfer device system comprising: a. providing a vapor-compression heat transfer device comprising a heat transfer circuit, a compressor having an inlet side and an outlet side, a refrigerant and lubricant reservoir, wherein said reservoir is in fluid communication with the inlet side of the compressor and with said heat transfer circuit, and said heat transfer circuit is in fluid communication with said outlet side of the compressor; b. determining the lower, compressor inlet side operating temperature range of the vapor-compression refrigeration device; c. determining the upper, compressor outlet side operating temperature range of the vapor-compression refrigeration device; d. selecting a refrigerant selected from hydrofluorocarbons (HFCs), hydrofluoroolefins (HFOs), hydrochlorofluorocarbons(HCFCs), hydrochlorofluoroolefins (HCFOs), hydrocarbons (HCs), carbon dioxide, ammonia, or mixtures thereof at a first concentration and selecting a lubricant selected from polyalkylene glycols (PAGs), polyol esters (POEs), polyvinyl ethers (PVEs), polyglycols, polyalkylene glycol esters, alkyl benzenes, mineral oils, polyalphaolefins, or mixtures thereof at a second concentration to produce a fluid system wherein said refrigerant and said lubricant are miscible at a first temperature within said lower, evaporator discharge operating temperature range and produce a fluid system having a refrigerant-rich phase and a lubricant-rich phase at a second temperature within said upper, compressor discharge operating temperature range provided that said second temperature is higher than said first temperature, wherein the lubricant-rich phase has a higher density than the refrigerant-rich phase at said second temperature and wherein the phase inversion temperature is between the lower, evaporator discharge operating temperature and the upper, compressor discharge operating temperature and the phase inversion temperature is at or below the temperature of the receiver or reservoirs and wherein the temperature in the compressor is above the phase inversion temperature; and e. introducing said refrigerant and lubricant into the vapor-compression heat transfer device. a. providing a vapor-compression heat transfer device comprising a heat transfer circuit, a compressor having an inlet side and an outlet side, a refrigerant and lubricant reservoir, wherein said reservoir is in fluid communication with the inlet side of the compressor and with said heat transfer circuit, and said heat transfer circuit is in fluid communication with said outlet side of the compressor; b. determining the lower, compressor inlet side operating temperature range of the vapor-compression refrigeration device; c. determining the upper, compressor outlet side operating temperature range of the vapor-compression refrigeration device; d. selecting a refrigerant selected from hydrofluorocarbons (HFCs), hydrofluoroolefins (HFOs), hydrochlorofluorocarbons(HCFCs), hydrochlorofluoroolefins (HCFOs), hydrocarbons (HCs), carbon dioxide, ammonia, or mixtures thereof at a first concentration and selecting a lubricant selected from polyalkylene glycols (PAGs), polyol esters (POEs), polyvinyl ethers (PVEs), polyglycols, polyalkylene glycol esters, alkyl benzenes, mineral oils, polyalphaolefins, or mixtures thereof at a second concentration to produce a fluid system wherein said refrigerant and said lubricant are miscible at a first temperature within said lower, evaporator discharge operating temperature range and produce a fluid system having a refrigerant-rich phase and a lubricant-rich phase at a second temperature within said upper, compressor discharge operating temperature range provided that said second temperature is higher than said first temperature, wherein the lubricant-rich phase has a higher density than the refrigerant-rich phase at said second temperature and wherein the phase inversion temperature is between the lower, evaporator discharge operating temperature and the upper, compressor discharge operating temperature and the phase inversion temperature is at or below the temperature of the receiver or reservoirs and wherein the temperature in the compressor is above the phase inversion temperature; and e. introducing said refrigerant and lubricant into the vapor-compression heat transfer device.