2001 Buick Park Avanue - HVAC intake

I'm wanting to fog the HVAC system (without taking it apart), so as to get rid of any mold/mildew that may be inside.

This might not be a good idea because fogging will put water vapor into the system and may short something out, but I'm willing to take that chance. So it blows a fuse - replace it, wait until it dries, and all will be good (?). Anyway....

First though, I fogged the interior carpets and the trunk, and I"m letting them dry.

Here's the problem: When I first start up the car in the morning, there's a pretty strong mold/mildew smell, and because I'm allergic to them, I need to find out where it's coming from and then eliminate it.

If it comes down to fogging the HVAC system (as a last resort), where are the intake vents for the system? I think they are under the windshield on the engine side of the firewall for normal operation. But what if I put it on "Recirc"? Where does it pull the cabin air from in that case?

And where in the air-flow circuit is the cabin filter? (Whoever designed the cabin filter was insane.... it's under the dash and behind the gas pedal in an almost inaccessible place, and the way it's designed, and how it's replaced is the craziest piece of engineering I've ever seen.) I'm wondering if the cabin filter may be mildewy or moldy. I replaced it not long ago, and it seemed to help for a little while, but not permanently.