We don't have AC at home, but I notice my sinuses, etc. act up if I'm in a store where it's too cool.
Oddly enough, fans don't bother me, but if I'm in a car with the windows rolled down for a period of time, I notice my hearing isn't as sharp, and my sinuses get a little more touchy.
Not pretty, but I gently stuff small pieces of cotton verrrry carefully in my ears. Obviously, if anyone tries this, do not poke the cotton in very far ---make sure it's just 'sitting there' and can be easily pulled out (my hair is long enough, so nothing shows). Make it super easy to remove.
I don't know why exactly, but this helps, and often helps me when I have a headache, too.
I'm always amazed that even a drop of about 10 degrees can negatively affect me.