Same exact scenario I found in my '98...

 

I recently changed the cabin air filter in our 1996 Lexus ES300. I found a YouTube video that showed me how to access the cabin air filter compartment by pulling back the carpet by the gas pedal. It does seem ridiculous that it is in such a tight space difficult to access. I too, realized that the vehicle did not have a cabin air filter installed. I bought a new one from auto zone. Before installing I had to vacuum out the compartment as best as I could because it was filled with debris. You can't really see in the compartment, even with a flashlight because of the angle. There are actually two filters. I didn't know which side the filter should face (didn't know if it mattered) so I just put the first one in and pushed it up the best I could and then had to figure out how to slide the next one into the grooves of the one that was already pushed up so that it would go in properly. I still don't know if it's installed correctly but they are in there. I noticed that after the filters were installed the pressure of the air coming out of the AC vents was no where near what it was before the filters were installed so maybe I have them in backwards or maybe that's the way the AC should have been blowing all along. I will likely stop by a mechanic so that they can look and see if it's installed the way it should be. Hopefully, since I already did the work they can just give some friendly advice and not charge.