SL1 Heater/Air Cond not blowing hard?

Hi all. The vents in my car do not blow as hard as they used to. This has actually happened before. It got to the point where they hardly blew at all, then one night, I heard something, I guess, push its way through whatever it was clogged in within the system, and then, magically, the air blew HARD.

Now I'm back to below maximum airflow. It blows hot, but the cabin takes forever to warm up (or cool down, depending on which season it is). This is especially problematic when my windshield is fogged over, and I need it to clear up.

Low and behold, I opened the hood, and, for the first time ever, noticed the screen on the air inlet hole right above the firewall (or whatever it is called, don't know the technical term for it). Sure enough, it wasn't even completely secured down to the surface of the car. So I'm assuming it wouldn't be too far-fetched to assume that something got in there and is clogging up the system.

So, finally to the point - where should I start in trying to fix this problem? Will I need to take the dash completely off and troubleshoot from there? If I need to do this, can someone link me to a diagram showing how this is done?

Thank you very much in advance for your help with this matter.

Jake