vacuum not switching at dash buttons

In my 65 barracuda the vacuum is not switching to the diff positions( defrost- heat). I verified I have 12 inches of motor vacuum going into the back of the button panel but nothing changes when I go from defrost to heat unless I move the the rods by hand. I also verified the vac diaframs work and do not leak. They will function with a hand pump using 7 inch vac. This car was once an AC car but all is removed. without removing the panel was there any AC vacuum attached to it? What is my possible issue and how to fix it.