The ornamental design for a portable airconditioner, as shown and described.
FIG. 1 is a front elevational view of a portable air conditioner showing our new design;
FIG. 2 is a rear elevational view thereof;
FIG. 3 is a left side elevational view thereof;
FIG. 4 is a right side elevational view thereof;
FIG. 5 is a top plan view thereof; and,
FIG. 6 is bottom plan view thereof.
The broken-line disclosure in the views is understood to represent portions of the article in which the claimed design is embodied, but which form no part of the claimed design.