Thermally stable lubricants for refrigerator systems

A compressor refrigeration system employing a fluorocarbon refrigerant, having a lubricant composition in contact with the fluorocarbon refrigerant, the lubricant composition having chemical and thermal stability in the presence of the fluorocarbon refrigerant, the lubricant composition consisting of a thermally stable oil of a viscosity at 100.degree. F. of from 100 to 300 SUS containing from about 5% to about 20% of the weight thereof of a liquid halogenated compound selected from the group consisting of diphenyl ethers and biphenyls and alkyl derivates thereof having at least one halogen substituent selected from the group consisting of chlorine, fluorine and mixtures thereof, the liquid halogenated compound being substantially completely soluble in the oil over the expected temperature range of the refrigeration system, the compound providing for good lubricity in the lubricant composition at cold startup, and at hot compressor operating temperatures while in vapor contact with hot fluorocarbon refrigerant, and the lubricant composition being highly resistant to chemical reaction with the fluorocarbon and/or the materials in the refrigeration system at the expected temperatures and operating conditions of the refrigeration system.