Originally Posted by Trevelyn1015
it does re-route to the defrost...
so, what do i need to look at to fix this?
Originally Posted by rwenzing
If it does, it probably means that you either have a vacuum leak somewhere from the vacuum reservoir to the AC servo diaphragms or the check valve in the reservoir is not working.
Look for a cracked vacuum reservoir (plastic sphere under the air cleaner), melted/cracked vacuum lines between the reservoir and the HVAC plenum or leaks in any vacuum lines or servos under the dash. There's also a small chance that the check valve in the reservoir isn't doing its job.
It would help if you had a hand vacuum pump (Mityvac) or could borrow one.