My Mom says that every time the AC unit kicks on, she can smell mold or an "old house" smell coming from the vents. I cant smell it though, but I guess she has a better nose than I do, plus Im extremely allergic to mold and also have a lung disorder where when something Im allergic to gets in my airway and irritates it, my bronchial tube will tighten up alot, once or twice it almost siezed the airway off to my lungs completley, which sucks. But I would think that with this condition I have, and mold being one of the things Im allergic to, that I would be affected by it. I dont know. If anyone can tell me ways to test it, or what it more than likely is and how to fix it I would greatly appreciate it. Thanks.