Awful smell from ventilation ducts

[billschroeder5842]

Originally Posted by A26B

Humidity will condense on the exchange & drain through a pipe onto the ground. Almost always visible after stopping for a bit. If you do not see a puddle near the firewall on the passenger side, then condensation may be accumulating in the air box. it will smell very musty. The drain pipe is usually a rubber and somewhat flattened on the end.

This would be my bet as well.