Refrigeration passive defrost system

A refrigeration system includes a compressor, a condenser, an expansion throttle, an evaporator and a control valve. All of the above elements are connected in series, in that order, in a refrigerant flow relationship. During periods in which the compressor initiates a passive defrost mode, control valve disposed within the conduit connecting the compressor and the evaporator remains open. Liquid refrigerant, by force of gravity, drains from the bottom of evaporator through the conduit to the compressor. This draining liquid refrigerant is evaporated by the hot compressor, flowing upward to the cold evaporator surfaces and condensing. The condensation releases latent heat of vaporization and heats the surface of the evaporator melting ice buildup thereon. In another embodiment, the refrigeration system further includes a bypass line connecting the compressor to the top of the evaporator. The inclusion of the bypass line allows the flow of the evaporated refrigerant to flow directly from the compressor to the evaporator through the bypass line, and the flow of liquid refrigerant to flow directly from the evaporator to the compressor through the conduit, such that no counter-current liquid and vapor flow within one conduit is required.