99 Sentra GXE Blower Motor

My blower began making a terrible racket (as though the fins were hitting a bunch of marbles)and eventually stopped completely. Are the motor and fan easily accessible? Is there a diagram available?

It depends on what you call “easily accessible” - most often you will find this up under the dash behind the glove box. It can require some acrobatics to get to it and work on it, but its not unreasonable.

You may be able to get the basics from Autozone’s online repair manuals - register at their site, plug in the car info and go to repair info. For $20 you can also pick up a Haynes or Chilton’s manual for it.