Originally Posted by maromeo
Anyone have any ideas?
Entirely possible that the oxidation and pigment from your rubber roof is washing into the A/C from the outside of the roof when it rains, settles in and then the water dries. It's a very fine dust that you would see sometimes when you wash your roof. But if it's leaking past the roof seal for the A/C unit, then drying out, could be blowing everywhere inside the unit.