a refrigerated display cabinet of the open top or open front type having a conduit extending around a storage and display space in the cabinet between an inlet and an outlet , refrigerated coils located in the conduit , air circulating fans for propelling air through the conduit over and / or around and / or through the refrigeration coils in a first direction during a refrigeration cycle , and in a second substantially opposite direction , during a defrost cycle , whereby during a defrost cycle ambient air is drawn into the conduit through the outlet and is passed around and / or through the refrigeration coils to defrost same , a supplemental defroster located in the conduit upstream of the refrigeration coils in the direction of air flow through the conduit in the defrost cycle ; and , a sensing and control mechanism coupled with the supplemental defroster for sensing defrost conditions during the defrost cycle and for energizing the supplemental defroster means upon the detection of an abnormal defrost condition to thereby accelerate the rate of defrost .