A/C Works in back, not front

[willsmith11111]

I have a 2008 97x. My A/C works fine in the rear but in the front it won't change between low and high. If it is blowing on low and I put it up to high and put it in neutral and restart the car, it sometimes starts blowing on high. Since the rear works I ruled out a compressor problem. I'm thinking maybe the blower motor but I'm hoping to get suggestions before I spend the money on a new one. Thanks for any help.

[Jc-place]

Check vacuum lines going to AC. i had this happen on a buick and found a worn spot pin hole leak in the hard plastic vacuum line under the hood(in my case under coolant tank!). Not sure how Gm does this in the SUV but it is worth looking into. The vacuum suction is required to switch vent from floor vents to upper vents. Car is impossible to cool stuck in floor vent setting. Good luck, let us know what you find.