Defroster does not work

On my 94 GA the heater controls are stuck in the vent position. ( The control rotates but the air only comes out of the vents. No defrost, floor, etc.) This is vacumn controlled. Took apart the control and tested for vacumn in each of the six lines. Only one has a slight reading (moves the gauge). Is this the normal state? Should one of the lines have full vacumn all the time? Will replacing the switch solve the problem?

Any advice and guidance is appreciated.

While you were in the dash did you see a black line to the control ? Thats the one you need to follow out of the firewall. Or look under the hood near the A/C lines to see if you can follow it from there I've even seen a few that the vacuum line goes in with the main wiring harness. 99% of the time the problem is under the hood.