Cooling coil and air distribution system defrost means

In combination, a refrigerator cabinet having an insulated above-freezing food storage compartment and a freezer food storage compartment therein, an evaporator compartment separated from said compartments, a source of electrical power, an evaporator having forward and rearward edges in said evaporator compartment, fan means for circulating air via inlet conduit means from the food storage compartments in thermal exchange relationship past said evaporator in a longitudinal flow path from the forward to the rearward edges thereof, exit conduit means for returning the cooled air to said food storage compartments, a compressor for supplying liquid refrigerant to said evaporator, electrical defrost heater means for periodically warming said evaporator to defrost temperatures, defrost thermostat switch means for limiting the duration of the defrost periods, temperature responsive cold control switch means for energizing said compressor, a defrost timer switch for periodically energizing said heater means defrosting said evaporator, said defrost timer means including a switch for selectively energizing either said compressor or said electric defrost heater means, the improvement wherein bracket means supporting said defrost heater means at the forward edge of said evaporator, bracket means supporting said defrost thermostat in heat exchange contact with the rearward edge of said evaporator for sensing the flow of air leaving said evaporator, control circuit means electrically connecting one side of said defrost thermostat to one side of said power source and the other side of said defrost thermostat with one side of said defrost heater means, said defrost heater means having its other side connected to a first fixed contact of said defrost timer switch, said circuit means connecting one side of said fan means with said other side of said defrost thermostat, said circuit means connecting the other side of said fan means with a movable contact of said defrost timer switch, said defrost timer movable contact connected by said circuit control means through said cold control switch means to the other side of said power source, a second fixed contact of said defrost timer connected by said circuit control means through said compressor motor to said one side of said power source, whereby said fan means is energized in unison with said defrost heater means upon said defrost timer movable contact being moved into contact with said first fixed contact to start a defrost cycle, and whereby upon said defrost thermostat sensing a predetermined above-freezing temperature of air leaving the rearward edge of said evaporator after frost on said evaporator has melted said defrost thermostat deenergizes said defrost heater means and said fan means, said control circuit means causing said fan means to remain deenergized until said defrost thermostat senses a predetermined below-freezing temperature of air leaving the rearward edges of said evaporator fins after moisture remaining on said evaporator has been refrozen after defrost, thereby resulting in a minimum of moisture laden cooled air being circulated through said exit conduit means to obviate accumulated frost buildup therein and whereby the run time for said fan means is minimized.

In combination, a refrigerator cabinet having an insulated above-freezing food storage compartment and a freezer food storage compartment therein, an evaporator compartment separated from said compartments, a source of electrical power, an evaporator in said evaporator compartment having refrigerant carrying coils equipped with a plurality of longitudinally extending fins, fan means for circulating air via inlet conduit means from the food storge compartments in thermal exchange relationship past said evaporator in a longitudinal flow path from the forward to the rearward edges of said fins, exit conduit means for returning the cooled air to said food storage compartments, a compressor for supplying liquid refrigerant to said evaporator, electrical defrost heater means for periodically warming said evaporator to defrost temperatures, defrost thermostat switch means for limiting the duration of the defrost periods, temperature responsive cold control switch means for energizing said compressor, a defrost timer switch for periodically energizing said heater means defrosting said evaporator, said defrost timer means including a switch for selectively energizing either said compressor or said electric defrost heater means, the improvement wherein first support bracket means attached to said evaporator supports said defrost heater means at the forward edge of said fins, second support bracket means attached to said evaporator supports said defrost thermostat in heat exchange contact with the rearward edge of one or more of said fins for sensing the flow of air leaving said evaporator, control circuit means electrically connecting one side of said defrost thermostat to one side of said power source and the other side of said defrost thermostat with one side of said defrost heater means, said defrost heater means having its other side connected to a first fixed contact of said defrost timer switch, said circuit means connecting one side of said fan means with said other side of said defrost thermostat, said circuit means connecting the other side of said fan means with a movable contact of said defrost timer switch, said defrost timer movable contact connected by said circuit control means through said cold control switch means to the other side of said power source, a second fixed contact of said defrost timer connected by said circuit control means through said compressor motor to said one side of said power source, whereby said fan means is energized in unison with said defrost heater means upon said defrost timer movable contact being moved into contact with said first fixed contact to start a defrost cycle, and whereby upon said defrost thermostat sensing an above-freezing temperature of air leaving the rearward edges of said evaporator fins after frost on said evaporator has melted said defrost thermostat deenergizes said defrost heater means and said fan means, said control circuit means causing said fan means to remain deenergized until said defrost thermostat senses a below-freezing temperature of air leaving the rearward edges of said evaporator fins after moisture remaining on said evaporator has been refrozen after defrost, thereby resulting in a minimum of moisture laden cooled air being circulated through said exit conduit means to obviate accumulated frost buildup therein and whereby the run time for said fan means is minimized.