We claim, the ornamental design for a air conditioner, as shown and described.
FIG. 1 is a front perspective view of a air conditioner showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left-side view thereof;
FIG. 5 is a right-side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is an enlarged cross-sectional view thereof taken along line 8-8 in FIG. 2.
The broken lines in the drawings illustrate portions of air conditioner which forms no part of the claimed design. The dash-dot lines in the drawings illustrate the boundaries of the air conditioner which form no part of the claimed design.