In the living room area, in the ceiling are 2 small rectangle grills that have the filters in them.
You will need to go to Lowes, Home Depot, etc. and buy window A/C replacement filters. They are a flat sheet of foam material. Cut to size, which on mine is cut the sheet into 1/2 or 1/3, I forget.
While you have the grills off, look at the foam returns. There have been reports of the returns sucked almost closed.
2012 Ram Laramie 3500 DRW 4x4 3.73 Tow Max Pkg B&W Companion 60 gal RDS aux fuel tank. 2014 Montana 3150RL, 2 A/C's, Leather, 6 Point Jacks, Splendede WD2100XC, Mor/ryde X-Factor, Duravis 250 tires with TST 507RV monitors. 2 x Honda EU2000's