<VV> Need some more non-corvair advise

[Grant Young]

I am trying to avoid a nasty GM repair bill if possible, so if you are saavy in the ways of late model GM air conditioning controls please drop me a private reply. My daughter's '04 Tahoe with dual automatic climate control air has decided to only blow hot air out the two vents on either side of the driver. The other vents in the front and the rear air work fine. Oh, for the days of a lever that went back and forth for heat and air! If you can point me toward the offending soleniod or control or whatever, I would deeply appreciate it. 
Thanks,
Grant