Hot water in the temperature from +50°C to 60°C is generated when refrigeration and refrigeration are operated, or the energy saving system is provided through the multi-function of hot water generation. In addition, self-diagnosis hot gas conduction with differential pressure damper control signals can result in additional energy savings. As a multi-unit cooler is formed in one freezer, one cooler is defrosted, and the other cooler forms defrosted cycle, the temperature deviation of the freezer is minimized.