this is a common problem in areas with high heat and humidity.
i have the exact same issue with my current (and 3rd) porsche.
the first one i fixed, because i had a leaking evaporator, so i had to get there anyway.
on the second i didn't care as it was my second car.
my current porsche is my daily driver, and this thing is really annoying me.
maybe a winter project all over again
http://986forum.com/forums/performance-technical-chat/36713-ac-question.html