I've got a '96 Olds LS with the manual climate controls.
When I'm cruising down the highway getting my 30.5 mpg with the air on, sometimes the vents seem to close, and no air some out anywhere, and just barely out of the vents, so the interior starts to get warm. I've figured out that if I shut off the a/c (it'* a seperate button on mine) in a few minutes, the air starts flowing full force out of the vents, and I can turn the a/c back on. On a long trip, I have to repeat this little procedure throughout the day.
It'* almost like the flap closes inside the system.
It only happens in the summer running the a/c.
Some have suggested a vacuum leak, but I don't know. I'm wondering if the coil is freezing up, and turning off the a/c lets it thaw the ice off and flow air through it again.
What'* weird is I use to have an '84 Olds 88 (rwd) that did the exact same thing, and i had to move the lever to vent and in a few minutes air would start flowing again, then I could put it back on a/c for awhile.

Suggestions?

No air coming out of the defrost vents or floor vents when this happens?

Nope.
It sounds like the doors closed inside the system. I suppose it'* vacuum related.

Yeh my friend had this happen on his Cutlass and needed a new vac ball... Maybe this is your problem it sounds as if it is.

I'm not convinced it'* vacuum. Usually a lack of vacuum directs air to the defrost and floor. Try pulling the vacuum source from the tank to see if you can duplicate the problem.

I think your evaporator is becoming clogged. Either by ice or wet oily stuff. Is the freon line back to the compressor freezing up? You may want to have the pressures checked on your A/C.

Yeah I suppose if you charged it yourself maybe and put to much poundage of freon in the system it could cause this problem? Yeh definatly get the pressure checked. The correct pressure should be on a sticker under the hood somewhere I think. :?:

2.2 to 2.5 times ambient temperature on the high side

This is what I was thinking. I'll get it checked.

Thanks doods.