1998 Buick Century Air flow

Does changing the fan speed do anything? Can you hear the fan speeding up and slowing down?

Yes, there is a cabin pollen filter. I have attached a picture showing where it is and how to remove and replace it. Don't leave it out as doing so can cause other problems with the HVAC system.

Yes, fan changes speed and air flow, but it is like it is restricted regardless of speed.

You might want to pull the blower motor to see if there are any obstructions there. If not, use a vacuum and some sort of flexible hose to see if you can vacuum anything out of both the inlet and outlet. Do the same from the cabin filter side. Be careful though. You may have had a critter crawl up there to die. Do you have any weird smells in the cabin at all?

No smells, fan changes speed. etc. Just does not have the output volume it should or like most other cars.

Well, before we go tearing deeply into it, pull the blower and pollen filter and make sure there aren't any obstructions.

Changed cabin filter for small gain. The problem seems to be that the air flow does not change to mid, floor or windshield. The indicator on the dash control says it changes, but it does not. Putting it on re-circulate does not speed it up nor does vent.

Can you hear anything coming from the airbox (sounds of movement, etc) as you move the selector switch around lowly?

Not sure what air box is. Any diagrams available to send me?

The airbox is under the dash. It's what contains the heater core and the heat exchanger for the AC. Easier to get to are the blower motor and the blower case. I've got screenshots of the written procedure for taking these apart but our reference has no images of it.

Check to see if air is coming out of multiple outlets instead of just one set. Look for levers and actuating rods under the dash and see if they move freely and have complete range of motion.