Refrigeration system with auxiliary heat exchanger for supplying heat during defrost cycle and for subcooling the refrigerant during a refrigeration cycle

In a reversible refrigeration system of the type including a compressor having discharge and suction sides, a condenser, a liquid refrigerant receiver, an auxiliary heat exchanger, an expansion device and an evaporator interconnected in a closed circuit to provide a normal refrigeration cycle wherein refrigerant flows from the discharge side of said compressor, through the condenser to the receiver, then through the auxiliary heat exchanger and through the expansion device to the evaporator and back to the suction side of the compressor, and wherein flow of refrigerant through the auxiliary heat exchanger is optional during the normal refrigeration cycle;

• the improvement of apparatus including valve means operative at the termination of a refrigeration cycle and prior to initiation of a defrost cycle for connecting said receiver through said auxiliary heat exchanger to the suction side of said compressor while connecting the discharge side of the compressor to said evaporator with the flow of refrigerant from the evaporator flowing back to the receiver, and apparatus including valve means operative during a defrost cycle for connecting the discharge side of the compressor to one side of said evaporator while connecting the other side of the evaporator through said auxiliary heat exchanger to the suction side of said compressor with the flow of refrigerant from the receiver into the refrigeration system being blocked.