Has anyone yet been sucessful in solving the GM issue with the a/c switching around to the defrost/floor etc instead of the vents when put under load such as uphill,etc?

A friend of mine had a Lumina that is doing the same thing my Bonne' is and we refuse to pay dealer labor for the fix..........Thanks

mine does that at start up each time for about 30 seconds or so and then blows through the regular vents, haven't noticed it doing that on hills or under stress though. Not sure why it does it but it'* consistent.

I have a 96 Dodge pickup that had the same problem, it would go from vent to defrost when under a load, after some careful searching it turned out to be a vacum leak in one of the hoses. Hope this helps.