Abstract: A refrigeration system including a compressor, a condenser, and an evaporator in heat exchange relationship with a fluid deliverable to a space. The evaporator is connected to the condenser via an inlet line and to the compressor via a suction line. A refrigeration circuit is defined by the compressor, condenser, inlet line, evaporator, and suction line. A refrigeration mode of the refrigeration circuit transfers heat from the fluid to a refrigerant in the evaporator and accumulates frost on the evaporator. The evaporator, a bypass line connected to the suction line and to the inlet line, a portion of the suction line, and a portion of the inlet line define a defrost circuit that circulates refrigerant in a defrost mode to transfer heat from the refrigerant to the frost on the evaporator. The refrigerant flows by gravity from the evaporator to one of the portion of the suction line and the portion of the inlet line in the defrost mode.