Please read before posting that it is a vacuum leak.
My '00 JGC Laredo had air moving only out of the defrost vents. I traced the leak to a hole drilled in the vacuum tank done by the dealer when they put in a new fan relay. (A$$holes.) I fiberglassed the hole and reinstalled everything.
However; the A/C light only comes on when the mode selector is on defrost or blend defrost/floor. If you turn the knob to floor, recirc, panel vents, etc, the A/C light shuts off. Here's the interesting part. If i push the rear window defrost button in hard enough, I can make the A/C light come on regardless of the position of the mode knob.
I've got the dash apart right now, and have located the power/ground for the HVAC panel, but without a diagram, i'm not sure what i should be looking for. I have read of other people having this problem, but none of them have posted a solution.
Please help !