I have an '82 and have an interesting a/c related problem.

I can only get air to come out of the center vent below the dash and out of the defroster slots on top of the dash no matter what setting is on. I know there is a leak somewhere but I thought somebody might have had the same problem and be able to help point me to where it might be.

You need to check and verify your vacuum source to your a/c heater control switch. Just below the blower motor housing you should see two vacuum lines exiting the firewall, one will be attached to the heater control valve on one of your heater hoses, and the other will be attached to the intake manifold, (this is the one to check.)

Thats part of the problem i have two one is a faded dirty purple and the other is black and i'm not sure which one goes where. That and the original lines are so brittle and kind of hard to work with.

The black one is vacuum source from the vacuum bottle to the a/c selector switch. The purple one is for the heater control valve and goes from the switch to the heater control valve. You need to replace you brittle lines, probably your problem right there.

are these lines something I can pick up local auto store or do I need to get some made for this application. I remember looking for lines fore something else and don't remember seeing any this small.

You can purchase it at most parts houses.

I basically had the same problem. I replaced both vacumn switches on the A/C head which I got at the local parts store. Works like new switching from heater to defrost, etc.