We claim the ornamental design for an air conditioner, as shown and described.
FIG. 1 is the front perspective view of a first embodiment of an air conditioner showing our new design;
FIG. 2 is the front view thereof;
FIG. 3 is the rear view thereof;
FIG. 4 is the left-side view thereof;
FIG. 5 is the right-side view thereof;
FIG. 6 is the top view thereof;
FIG. 7 is the bottom view thereof;
FIG. 8 is the bottom perspective view thereof; and,
FIG. 9 is the enlarged view of the encircled portion in FIG. 2.
The broken lines illustrating portions of the air conditioner form no part of the claimed design. The dot-dash broken lines in the figures represent a boundary line and form no part of the claimed design. The dot-dot-dash broken lines encircling portions of the claimed design that are illustrated in enlargements form no part of the claimed design.