Air conditioning and heating not working

So I’m having trouble with my ac and heating system in my car it just blows whatever air is outside and I wanted to see if it could be a easy fix what I’ve done to it already is I’ve taken the fan out and replaced it so that it blows we have tried to put Freon in the system and that didn’t work I’ve replaced the cabin air filter but that did nothing and what I’m looking at now is the engine bay air filter which is filthy I was wondering if it could be that’s somehow stopping it from working or if it’s something else