Auto Air Conditioning & Heater Repair: air conditions 1997 tahoe, dash vents, dash panels

Question
My 1997 tahoe air condition dont come out the dash vents when on high when on low its fine you turn up you hear it shut and all goes to defroster.Put new controls and didnt fix do you have any suggestions.And by the way does come out on floor

Answer
Craig,
Inside your ducting in the dash, there are several doors that open and close sending the air to wherever you want to as set by the control head. Being that you have already replaced the control head, that rules out the wrong signals being sent from it.
There are two systems that car manufacturers use to operate these doors. I am unsure of which type your truck uses.
The first is a vaccuum type system in which the control head sends electrical systems to a vaccuum control manifold. This vaccuum control manifold then translates these signals into vaccuum being pulled on a series of vaccuum lines. These lines lead to the door actuators themselves and open the appropriate ones. If this is the type of system your truck uses, then it is very possible that the actuators are receivign a weak vaccum signal and with the pressure created by the high speed air, it is unable to keep the doors open. This could be several things. A dry-rotted vaccuum line may be losing some of its vaccuum through a crack or pinhole, or it may be the connection at the actuator itself or at the VCM is loose and losing its vaccum from there. Or it may even be that your vaccuum control manifold is going bad. The diaghrams inside it may be worn out.
If you have the all electrical system, that would lead me to zero in on the actuator or motor itself weakening and closing as the high speed air passes over it.
Either way, I highly recommend you taking this to a reputable A/C shop or even the dealer to troubleshoot. It is a fairly in-depth process finding a fault inthese systems, the largest part being the disassembly of the dash panels and ductworking. They should also have the appropriate diagnostic equipment that would make this job much easier and quicker than one person in his garage.
Thank you for the question, and I hope that I was able to help you out just a bit. If I can be of any more assistance now or in the future pleaselet me know.