So just this past weekend the ac started to smell. The smell almost smells like the holding tank. The holding tank isn't anywhere near the ac until. I cleaned the air handler filters in the beginning of the season. What would be causing this smell and how can I fix it. I am going to treat the holding tank but I am not sure that's the cause of the smell, the engine room doesn't smell and that's where the ac unit is located. Could a dirty strainer cause this smell? I did a quick peak yesterday and the strainer looked clean it wasn't all dirty and black. Where would you guys start? It's definitely a foul smell.