I have a 2002 Thor 18DT with a Dometic 57915C a/c unit, which I believe is the original. Recently, there has been a musty smell when I turn on the a/c. The interior filter seems OK. Is there a filter that needs to be changed from the roof?
Kodachrome Time Machine, my vintage photo collection from the 1940s to the 1970s: https://www.youtube.com/channel/UCff0z54NyAfuAjUST896l6g
My truck does that sometimes. Condensation grows mold and such. Try leaving just fan on for a few minutes with A/C off. Cleaning coils will probably clear it for awhile but will come back.
Recently cleaned the cooling coil on roof. Have to take it apart to the point you can see inside camper from roof. Used a foaming cleaner and rinse with water from spray bottle. Used towels to keep water from entering camper. Smells lemony fresh now!