It's most likely in the vents.... Residual moisture from the condensor can accumulate and cause mold and mildew in the intake vents... There are some spray cleaners to rid the vents of the mold, but you'll probably need an air purifier/Ionizer like this to get the smell out afterwards:
UV Air Purifiers Ionic Electronic Air Cleaners UV Ionizers Ozone Generator HEPA Systems Home Air Cleaner Purifier Filters