I have a problem with the air control defaulting to the defrost position, I cant find any visible vacum leak. Is there something that can help me track down this problem.

First place I would look is under the hood.
Trace all vacuum hoses coming through the firewall.
Chances are it is rotted.
It could possibly be in the switch that regulates vacuum as well.
Just be thorough and you'll find it.

Fordman123