Ok Guncho, HVAC 101.
You need the same total input, as you do output.
3 bags O stuff in , 3 bags O stuff out. Your home should be a closed "balanced" system or it will work to hard tryin to push 1 bag out if it becomes unballanced. The adjustable vents are there to help fine tune the balance, you do not really touch those after they are set or it gets kind of "backed up" so to speak. Like if you where to cinch up your belt after eating a large pizza yourself.
And basements need airconditioning in the summer most of all, it keeps the humidity lower and helps the A/C unit to work better. Your actually making it work really hard when you close those vents in the summer to the basement.
That's why the pro's get the $$.They go to lots of school to figure these things out.
Hope the analogies helped.