Abstract: An apparatus for providing cool air to electronic module cabinets wherein a plurality of electronic modules are stacked within a cabinet such that front surfaces of the modules face a front cabinet opening, the apparatus including a plenum door assembly having an inlet for receiving cooling air and a plurality of outlets, the outlets positioned proximate the front faces of the electronic modules so as to provide cool air thereto, the modules in some embodiments having fans that draw air to back sides of the modules opposite the front surfaces, the plenum openings being adjustable to modify the amount of cooling air being delivered to the modules.