Diagnosis
The air filter on the FFAD7033R1 is a simple foam panel behind the front grille. It gets clogged with dust and can get wedged in there if it hasn't been cleaned in a while.
How to Fix It
Unplug the unit. Look at the front grille—there are two plastic tabs on the top-back edge. Press them inward (toward the center of the unit) and pull the entire front grille toward you. It should hinge open. The foam filter is right there. Gently pull it out. Rinse it under lukewarm water until the water runs clear, squeeze out excess water (don't wring it), and let it air dry completely before putting it back.
If That Didn't Work
If the grille still won't budge, check if there's a buildup of dust or mold along the bottom edge acting like glue. Use a flat plastic tool (like a guitar pick) to gently pry along the seam, being careful not to snap the plastic tabs.
Heads Up
Never run the dehumidifier without the filter. It'll coat the evaporator coils in dust incredibly fast, which kills efficiency and can lead to the 'freezing up/no water' problem. Also, make sure the filter is bone-dry before reinserting it to prevent mold.