Refrigerant cycle system having hot-gas bypass structure

A refrigerant cycle system for selectively setting a cooling mode and a heating mode, the refrigerant cycle system comprising:

• a compressor for compressing and discharging refrigerant;
• a first heat exchanger for condensing gas refrigerant discharged from said compressor;
• a first decompression unit for pressure-reducing refrigerant condensed in said condenser;
• a second heat exchanger in which refrigerant from said first decompression unit is evaporated during the cooling mode;
• a refrigerant pipe for defining a hot-gas bypass passage through which gas refrigerant discharged from said compressor is directly introduced into said second heat exchanger while bypassing said first heat exchanger and said first decompression unit during the heating mode;
• a second decompression unit disposed in said hot-gas bypass passage, for pressure-reducing refrigerant discharged from said compressor during said heating mode;
• a detecting unit for detecting a physical amount indicating a state of refrigerant flowing through said hot-gas bypass passage during the heating mode;
• and
• a control unit for controlling operation of said compressor,
• wherein said control unit determines a refrigerant shortage based on said physical amount, and stops the operation of said compressor when the refrigerant shortage is determined.