Filter was optional on earlier models then became standard, I think. If you do not have a filter, then it's safe to assume that you need the retaining bracket and the filter. They are easy to install. I don't recall but I think the retaining piece just fits in the opening and the filter snaps in place somehow. Sorry I can't be any clearer. I installed one in mine a couple years ago when folks thought this would prolong the evaporator. I don't know if it made a difference but I still have the original evap.