OK, not much need for AC much longer, but I need help ID'ing a problem. When I've had my AC on all summer, it smells musty, a little more so than it did last year.
Also it's mysteriously worse at some times than others, and distinctively worse in some rooms than others (more upstairs than down.) I've had the vents cleaned out in the spring, and the scent still exists. Any advice on how to rectify?