Rear A/C Problems

I have a 2000 Chevrolet Tahoe. My front A/C works fine, but my rear A/C doesn't blow at all. Whenever, I turn on the front A/C and then turn on the rear A/C, I hear a loud whinning noise and then the rear a/c shuts off and their is no air blowing at all. Where are some places I could check to see what the problem is? Thanks a lot.

Coop