Abstract: Apparatus for mounting an air conditioning unit upon the roof of a vehicle for providing conditional air to the interior of the vehicle. A frame is contained within an opening formed in the roof and the unit is mounted upon the frame so that the supply air opening and the return air opening of the unit communicate with the interior of the frame. A one-piece floor panel is contained in the frame upon which an adjustable partition is seated which divides the interior of the frame into two separate compartments. The base of the partition is secured to the floor panel and a movable top section is closed against the pan of the unit so that the supply air can move through one compartment and return air through the other compartment. The top section of the partition is adjustable and is furnished with thick resilient seals so that the mounting frame can be utilized in vehicles having different roof depths.