Pontiac - Grandprix :: Moldy Smell That Comes Out Of Vents After Shut Off Air Conditioning

I enjoy your show and newspaper column. Here's my situation. I have a 2008 Grand Prix with a stinky problem. There's a terrible musty, moldy smell that comes out of my vents (any vents, i.e. dashboard, floor, defrost) after I shut off my air conditioning. When just the fresh air from outside is coming through the vents, everything is just fine. When I turn on my air conditioning, everything is just fine. When I turn off my air conditioning is when the funky smell starts.

Mechanic number one cleaned out the drain hole, sprayed anti-mold spray and foam through the air intake vents with the recirculation switch on and the windows rolled up. But the mold is still there. Mechanic number two shared with me that the only way to get the mold out is to disassemble part of the A/C unit, physically clean out and disinfect the unit and then add some other part that drain or dry the unit so moisture never sits in there and starts the molding process. Is that the best way to deal with this problem?