93 fleetwood - bought new - sounds like water sloshing around behine the radio in the a/c ducts. also when fan is on, it blows out fog, like moisture in vents/ducts. is this a water drain/hole plugged up allowing water to flow where it isn’t suppose to. i can picture water flowing out of the vents in a heavy rain
There is an AC drain located on the firewall, passenger side just above where the firewall bends to an angle to the floor boards. It is a short rubber tube that makes a 90 degree bend downward right after it comes through the firewall. You can blow some compressed air up the tube or use a flexible rod of some kind, I use a nylon cable tie to clear mine out.