As far as explaining "passages" for the EGR:
The passages that get clogged ar actually part of the Throttle Body's mating surface. You remove the TB, and clean the little "grooves" in the TB, they get filled with gunk.
You'll need a new TB Gasket when performing this task, though.
Also, vacuum problems can affect your A/C, though I don't think the two are tied (but they may be!!) When you have only defrost mode, that is "no vacuum" operation (the default of the car). Search behind the console, by getting on the passenger side, and looking behind the HVAC area for the vacuum lines (hard plastic.. be careful they may be brittle) I suspect you'll find one that popped off the connector behind there.
Ray
