A/C question, why does white stuff come out?

[240sxspeedracer1]

Now be nice guys, save your dirty comments for later.
Ok, there is some white substance that comes out of the vents when I turn on the a/c and I'm not really sure what it is...
Today the white stuff didn't come out, but other days it has...is that a sign of the a/c running out of coolant or something?
TIA

Edit: It is kind of powderey and sticks to the panels. It doesn't have any smell,it's odorless.

[Natty]

Wierd. On ocassion, mycar will do that, excpet it's a gas, not a powder. I may try a new cabin HVAC filter, but until then, fark it :p

[the head]

mystery funk powder pull out your ac plenum and clean it out sounds like dust/fungus/cocaine/anthrax in your plenum this should not affect the operation of the system provided everything still works just disassemble and clean