An improved upright open front refrigerated display cabinet having primary and secondary air flow conduits, in which air flow directing means are provided for selectively drawing ambient air into the secondary air band conduit during a defrost cycle and for substantially preventing ambient air from entering the secondary conduit during a refrigeration cycle and for directing the flow of air through the secondary conduit in a first direction during the refrigeration cycle and in a second direction, substantially opposite the first direction, during the defrost cycle. Fans are provided in each of the primary and secondary conduits; the direction of air flow in the primary conduit remains constant at all times, during both refrigeration and defrost cycles. The secondary band fans propel air in a first direction (codirectional with air flow in the primary conduit) during the refrigeration cycle and in a second direction, substantially opposite the first direction during the defrost cycle whereby the ambient air is mixed with air propelled by primary fans in the primary conduit. Finally, means are provided for diverting air from the secondary conduit to the primary conduit during the defrost cycle and for substantially preventing the diversion of air from the secondary conduit to the primary conduit during the refrigeration cycle.