Disconnect all power in the building. Remove the cardboard sleeve stiffener from the wall sleeve. Remove the rear closure panel by folding the four flaps of the panel and pulling the entire panel out diagonally from one side.
Remove the PTAC cabinet front by grasping it and pulling the bottom of the cabinet front away from the chassis until the retaining clips disengage.
Insert the chassis into the wall sleeve. Slide the chassis into the sleeve until the chassis flanges contact the front edge of the wall sleeve. Drive three screws through the chassis flange and the wall sleeve on either side of the chassis using a screw gun.
Replace the cabinet front by slotting the front gently into place and then pressing down on the bottom of the cabinet front until the mounting clips engage.