Abstract: The inwardly-extending, peripheral frame of an air conditioner, exposed after the removal of the filter-enclosing cover thereof, grippingly receives U-shaped clamps thereon. The clamps have extending ledges to which are fixed upstanding studs. A cover, having a center recess, has outwardly extending flanges in which are formed slots. The studs are aligned with the slots and the cover is set thereover and wing nuts are tightened onto the studs to clamp the cover in place. The cover recess has a pad of resiliently compressible material fixed therein to prevent air drafts from passing through the air conditioner into the room into which the frame extends, and to dampen outside traffic noise, and other unwanted sounds.