I have a Lennox split system in my 1200 sq. ft. old house in Austin, TX. There is one return air grate in the middle of the house that seems to sit directly under the air handler, which is in the attic. When I bought the house last year, I seem to remember swinging that grate open and pulling out a 2-piece metal tray that I took out back and washed. Later I had someone else do some work on the ceilings and yesterday I pulled the grate open again and was shocked to see that the 2-piece tray unit was not there and that someone had laid some charcoal filter strips (for my portable HEPA unit) on top of the grate and left it at that. Does anybody out there know what the metal tray was and if it is necessary? It does appear that a filter with rigid sides could slide into the slot where the tray(s) used to be. The split unit is not really, really old, I don't believe (less than 15 years, I think) and the grate is about 36" by 15" in size. So, should I try to find a replacement metal tray thingy or should I just stick a filter up there where it used to be?

Thanks!

Mike