GMC Repair: GMC Sierra A/C Issue, gmc sierra, battery terminals

Question
Hey,
I know you said you prefer 99 or newer but i thought this may be a somewhat universal repair.  I have a 1995 gmc sierra and when i turn the a/c on it will only blow on my feet and from the defrost.  However, when the a/c is off and just the fan is on it will blow from all of the vents like its supposed to.  I have read several places to look for the door controls that are located somewhere in the dash.  So my first question is do you agree with this idea? and second how do i get my dash off so that i can access the areas i need to.  I have already taken off the protective cover that exposes the coils under the glove box, but that doesnt allow my to see what i need.  Also i have pulled the actual a/c controls out and that doesnt seem to help me find anything either.  Thanks a bunch.

Answer
Hi
Dont mind the older vehicles, just the schematics and location of items are getting harder to find.
On the drivers side is your mode door actuator and linkage.
Look up there and watch the movement of the linkage and the door.
I have replaced a few of the linkages.
I have also replaced a few of the actuators.
You MAY want to try this  trick first.
Unhook BOTH the positive AND negative battery terminals.
With them both off the battery, touch them both together for about 30 seconds.
Now rehook the negative first, then the positive.
Now give it a try. See if it works correct.
If so the controller was Logic Locked.
If not, then watch the movement of the actuator and linkage.
Just advice from experience.
I Hope this helps.
Good Luck
Pawl