Air not blowing out of vents
Blower motor resistor pack is likely bad. It works on its highest setting as that setting skips the resistor pack and applies full voltage to blower motor. So replace the resistor pack and you should be good to go.
Shana, to access the blower motor resistor (pretty simple job), need to take the plastic kick panel off below the glove box. After it's off, you can look up and see the big resistor with 2 small screws holding it in. Then drop the glovebox door completely down, need to release the spring on the side to access the resistor electrical connector that goes into the fan. Very common problem on our platform. I would recommend replacing the female pigtail that plugs into the resistor too. They tend to melt.
Search Chevrolet TrailBlazer Questions
Chevrolet TrailBlazer Experts
Related Models For Sale