I had dirty sock in the fall when my system was first installed last year. It was treated by cleaning and spraying the coils with a mold killer. No more problems....until this fall. It re-occurred. Tech called Trane and got a new product that contains a polymer and acetone. He cleaned the coils again and spayed them with this product. When dry, it feels like a plastic coating. Have any of you used this method and is it safe for the machine and humans? I suppose so but other opinions never hurt.