Refrigeration Cycle System and Automotive Air-Conditioning System Including the Refrigeration Cycle System

There are provided a refrigeration cycle system which ensures adequate lubrication in a compressor and operates at a satisfactory coefficient of performance despite use of a working fluid containing a lubricant and a refrigerant that separate from each other in a condenser, and an automotive air-conditioning system including the refrigeration cycle system. A refrigeration cycle system (12) comprises a compressor (28), a condenser (24), an expansion valve (26) and an evaporator (28) disposed in a circulation path (14) along which a working fluid containing a lubricant and a refrigerant that separates from each other at temperatures higher than a two-layer separation temperature flows, serially in a specified flow direction of the working fluid, and a lubricant return means for preventing the lubricant from accumulating in the condenser (24). The lubricant return means reduces pressure of the refrigerant in the condenser (24) to a saturation pressure of the refrigerant for the two-layer separation temperature or below, when the working fluid is made to flow along the circulation path in the specified flow direction and temperature around the condenser (24) is lower than the two-layer separation temperature.