A musty odor that worsens when the AC runs can point to hidden mold in ducts or the evaporator

https://coolairtroubleshooting972.evergrovio.com/posts/repair-or-replace-ac-a-homeowner-s-guide-to-smarter-cooling-decisions

A musty odor that worsens when the AC runs can point to hidden mold in ducts or the evaporator. Keep the filter fresh and arrange a thorough cleaning service.