probably would be helpful to identify the smell and/or origin prior to treating the
symptom vs root cause. in the interim, the other suggestions are good also....
including running with charcoal filter, or swapping out cabin filter -- even sprinkling
layer of baking soda on top of the filters, in hopes they'll neutralize, somewhat,
the offending odor. but yes, if mildew cause...or from A/C, treat the cause.
if vinyl, or air intake duct or user induced (accidentally), treatment will vary, natch

__________________
-- raymond~
47º 34'N 122º 18'W