Abstract: This invention describes an improved installation system for an air conditioning system which can be used for buildings, offices, or apartments usually where the roof is flat. It provides a shallow metal pan of cross-sectional area substantially that of the air conditioning equipment which is to be mounted on top of it. This pan is divided by a central wall into two plenums. There is an opening in the bottom of each plenum. The pan is mounted directly on the roof deck, and there is an appropriate opening in the roof deck immediately below the opening in the plenum. Means are provided for ducts to be connected between the openings in the plenums to extend through the roof to the ceiling of the room immediately below. A ceiling fixture, grill or diffuser is provided in the room, and the ducts are connected into the top of this ceiling fixture.