Temporary loss of air flow inside cabin

My new-to-me '93 is my daily driver and I run the AC almost every day in stop-n-go and short freeway driving with no issues.

But on my first long trip (SD to LA) somewhere between 50 and 100 miles in, I suddenly noticed there was no air flowing through any of the vents (dash, floor nor windshield). As I usually do, I leave the fan speed set to its lowest setting when at highway speeds. I stuck my little finger inside the vent and could still feel cold air seeping through (AC system still working). Naturally, I turn the fan speed up and can then hear air blowing around inside the dash...kinda sounded like a wind tunnel...but still nothing coming into the cabin. I slid the selector all the way to off until I reached a rest area. As I was coasting into the area, I re-engaged the AC and by the time I parked all was working normally again. Back up on the freeway, I'm guessing another 50 miles, problem returned.

I had something somewhat similar happen with my '87 CE and that turned out to be a vacuum leak. But do I understand by '93 the ventilation system was electrically controlled rather than by vacuum? Anyone ever experience this and have an idea what my issue might be? Thanks in advance!

Since you have the Caprice, it has a manually operated heater valve. The rest is vacuum controlled. Check your "mode" actuator valve. It is the only one with the two hoses to it. The multi vacuum connector or hose from it could also be your issue. Check for flow from the bottom "heater" vents when it is not blowing air from the dash vents. If you are getting airflow from them your mode valve is not functioning properly.

Was this in AC mode? Your evaporator might be icing up due to low charge or bum pressure switch.