Need to find the vacuum schematics for 2000 impala 3.8 A/C selector knob does not work, can't change air flow.

You don't need schematics, you need to find a vacuum leak. It could be within the climate control itself or in the feed line from the intake manifold. Either way, there's a couple of quick checks. One is to run the engine for about a minute, shut it down and without any interference(open windows, radio, blower fan running) listen near the control switch for a breathing sound as you swich from vent to defrost. If you hear this you're half way home. If you do not then you've got to find why there is no feed to the climate unit. Out side under the hood to the rear of the intake manifold there will be a series of vacuum lines connected to a "tree"one of these should veer off to a vacuum accumulator(colletor) this should be a large black, or white sometimes, ball with to spouts containing vacuum lines. One of these will go to the "tree" the other to the firewall. The latter is the feed for the climate control unit.Check to see if the one from the tree has suction by pulling it off the ball and touching it to your tongue. If it does not then check it's condition for cracks and check at the tree for blockage.This should leve nothing to question. If you have feed to the ball and out to the climate control and you hear the breathing sound when changing positions than you need to totally disassemble the heater box because the delector doors are hanging up somewhere.Best of luck my friend, Dana