Heat and A/C both work, but I select the dash vents and heat, almost no air is delivered. If I roll the temperature to the coldest setting, I get good air flow out the same vents. I pulled the panels from the driver and passenger side and I see a vacuum actuator on each side. If I move the air delivery **** on the dash from dash only to dash+floor to floor only to floor+defrost to defrost only, I see both of the actuators move and change the air delivery. I can also see the electric temperature actuator move when I change the temp from full cold to full hot. It's got three notches and they seem to correlate to full cold, full hot and a middle notch when the temp is set in the middle. I've also noticed that the air on the drivers side is slightly warmer than the air on the passenger side. This isn't a huge issue, but may be a symptom of the same problem. The only major repair I've had is the intake manifold gasket that seems to go bad on all of the v6 push rod Chevy's of this era. That particular repair was years ago. This issue is new. Any ideas?? Thanks, Al

 

My recently acquired 02 is the same way.

When I first got it there was no air flow either way, heat or A/C. It turned out that the cabin filters were severely plugged. Probably were never changed. You could hear all kinds of blowing going on under the dash but no air was coming out. New filters and the A/C is a bear but the heat is wimpy. Sounds the same, all kinds of blowing going on but no air coming out. Perhaps a restriction in the air supply to the heater core?