Abstract: An air deflection duct assembly is disclosed for use in adding an evaporative cooler unit to an existing refrigeration air conditioning duct to increase the efficiency of operation of the evaporative cooler by causing a higher percentage of the air flow from the cooler to pass into and through the existing refrigeration ducts. To accomplish this, first and second spaced apart duct assemblies are mounted over holes cut into the existing refrigeration air conditioning duct system. Each duct assembly has an adapter plate constructed with a circular hole in it, and this hole is normally closed by a pressure-opened deflector hinged at one edge of the hole. The hinged edges of the deflectors are mounted facing one another. When air is passed into the collar of the assembly extending upward from the hole from the evaporative cooler, the deflector plates open and extend at an angle into the existing refrigeration duct to deflect the air in opposite directions from the space between the openings cut in the duct.