2008 Audi TT Question mildew smell

Very likely you are right about the vents. If you have been using the air conditioning recently, it's job is only to lower air temperature around 20 degrees. The real comfort comes from removing the humidity. The moisture condenses on the cold evaporator in the dash and drips into a drain pan. There is a drain tube to take the water outside where it drips onto the ground. It's fairly common for the rubber drain tube to become blocked with debris and the water builds up inside. Often that water spills out when turning a corner.

The air conditioning also runs in the defrost mode to dry the air before blowing it onto the windshield. That prevents moisture from condensing on the cold windshield.

Look under the hood on the passenger side firewall for a 3" to 4" rubber tube with a right angle bend hanging down. Squeeze it to open it up and free and debris. If nothing comes out, there is usually a wire ring you can squeeze to remove the hose. Then you can carefully poke a pencil into the plastic tube to dislodge any leaves, dirt, or mouse nest parts.

Dealer's parts departments, and most auto parts stores have sprays to eliminate the mildew smell.

caradiodoc

Thank you for your suggestion. However, I am unable to locate the hose. Is 3-4" the length of the hose or the diameter? If it's the length, what is the diameter? Also, the smell is very noticeable in the trunk as well as inside the car. Does that change your diagnosis?

The hose is normally about 3/4" in diameter and 3-4" long with a right angle bend in the middle, but the Germans do everything different.

The smell can travel throughout the car. Look on the trunk floor too for signs of leaking weatherstrip.

caradiodoc