Abstract: An improved large capacity air distribution system for cooling electronic components mounted on printed circuit boards. The system has an air plenum chamber of substantially constant rectangular cross section. Openings are formed in the side walls of the chamber to permit air from within the chamber to flow outwardly in a direction substantially normal to the outer surfaces of the side walls and over the components to be cooled. A baffle in the form of a tapered wedge formed from a pair of thin metal baffle sheets is mounted in the plenum chamber so that the joined edges of the metal baffle sheets are positioned centrally in the air inlet of the chamber and the baffle is otherwise symmetrically disposed in the chamber. A large number of small round holes are formed through the sheets of the baffle, the area of the holes occupying a substantial percentage, approximately 36 percent, of the total area of the baffle. A high capacity air pump supplies air under pressure to the interior of the plenum chamber.