Abstract: CLAIMThe ornamental design for an air conditioner, as shown and described.DESCRIPTIONFIG. 1 is a front, top and right side perspective view of an air conditioner showing our new design, with the louver in opened position and the control panel cover in opened position.[...]. .Iadd.; .Iaddend.FIG. 2 is a front elevational view thereof with the louvre and control panel cover in closed position;FIG. 3 is a rear elevational view of FIG. 2;FIG. 4 is a top plan view of FIG. 2;FIG. 5 is a left side elevational view of FIG. 2, the right side being a mirror image of that shown; .Iadd.and, .Iaddend.FIG. 6 is a bottom plan view of FIG. 2.