The ornamental design for a cover for an aircompressor, as shown and described.
FIG. 1 is a perspective view of a cover for an air compressor showing our new design;
FIG. 2 is an end view; and,
FIG. 3 is a side view.
The broken line showing of an air compressor and associated equipment in FIGS. 1–3 is included for the purpose of illustrating environmental matter and forms no part of the claimed design.