I claim the ornamental design for combined dust cover and air filter for a fan blade, as shown and described.
FIG. 1 is a perspective view of a combined dust cover and air filter for a fan blade, showing my new design;
FIG. 2 is a front elevational view of the invention;
FIG. 3 is a rear elevational view of the invention;
FIG. 4 is a left-side elevational view of the invention, the right-side elevational view being a mirror image thereof;
FIG. 5 is a top plan view of the invention; and,
FIG. 6 is a bottom plan view of the invention.
The broken line showing of the fan blade and the fan blade iron is included for the purpose of illustrating environmental structure and forms no part of the claimed design.