I am in the middle of replacing all inside. 1979 L82.
Problem with vents only. Blower working fine. I unhooked the control valve plugs and air lines. Transferred over to a new unit. Turned on to test. Only blowing out of the floor heater vents left and right. Switch to vent, defrost and both AC stops, and no luck, keeps blowing out of floor with these on.
I went back to the factory unit. Same thing. There is only one way to plug these in on the control unit.
The lever on the box behind the glove compartment is working fine, full throw each way.
Would starting the engine do something to the vacuum lines here ?
I have gone back and read all forum questions and answer's with similar requests, but no help here.
If someone gets me an answer, I will send you a fish.
Thanks,
Boatman in south Florida

It's Fixed. I should have known. I had unhooked all of the air lines from the control unit. When you hook them back up, start the engine, this will fill the lines with air again. All working fine now.
Thanks anyway. No fish today.