A refrigerated glass door merchandiser in which heat generated during a defrost cycle of operation is prevented from flowing into the refrigerated display section. The glass door merchandiser is formed by a cabinet having an access opening in one of its walls with a glass door covering such access opening. The glass door is movable for enabling access through the access opening to products within the display section of the merchandiser. An air conduit extends around the cabinet and has an outlet opening at one end of the access opening and an inlet opening at the other end of the access opening. The outlet and inlet openings are arranged in alignment so that air circulated through the conduit and leaving the outlet opening is directed towards and received by the inlet opening for establishing a continuous air band around the cabinet and across the access opening during a refrigeration cycle of operation. As the air is circulated by a set of fans which are arranged in the air conduit, the air is refrigerated by a set of evaporator coils. During a defrost cycle of operation, both the air flow and the operation of the evaporator coils are temporarily terminated. Heat is applied in the area of the evaporator coils during the defrost cycle of operation for defrosting the coils. Since there is a natural tendency for such heat to rise by convection, the heat would eventually reach the interior of the display case. A heat trap mechanism is provided within the air conduit at a location subsequent to that of the evaporator coils along the flow path in order to prevent such flow of heat by convection during the defrost cycle of operation.