MY AIR ONLY WORKS ON SETTING 4 BUT WHEN I WANT TO TURN IT OB HIGH #5 IT STOPS?

you mean the blower motor only works on one speed?same thing happens with the heat on,only one speed?if so suspect blower motor resistor is bad.there are a few different ones for your vehicle!6 cylinder,or 8 cylinder,automatic temp. control,manual temp. control?

I had the same problem before you mess with the blower motor resistor try checking the wiring harness that goes to the resistor if that don't fix it try replacing the resistor if problem still exist try replacing the control switch but I had a Colorado that done same thing I spent a bunch of money on new resistor and blower motor and control switch and my problem still existed so I tried a new wiring harness and problem solved had same problem on my trailblazer wiggled the wiring harness around and high #5 started working again