What is the monstrosity that sits under my dash that manages, diverts and controls the flow of air, heat, ac into the cabin? What is this called? It is a seeming self contained unit. How do I remove it? Is there something in this housing that might interfere in any way with the free spinning ability of the blower, heater fan? My fan stopped and a bump would get it started [not an electrical short]. Soon it would start but a tap on the housing with a small hammer would free up something and it would spin up to speed. But now nothing will get it going. I am preparing to just replace the motor but access on in the engine compartment. What is inside this monstrosity that might be causing this symptom>? Thanks for your time and help.

You have a 20 year old car. The motor may just be worn out. Also dirty commutator or bad brushs on the motor.