Well, there goes my theory! Sorry, failed to notice your location. I am way north of you almost on the Canadian border. Slightly different weather. Does this happen to a lot of the systems there? Or is it isolated to certian homes? There is only a few months of a/c here. I'd love to visit, a/c and refrigeration work is my preference, but I work on heating systems most of the year. (go figure)
Would it be worth trying some bleach solution to kill the bacteria causing the mold? Does it occur in your split systems too?