My 92 Bonnie has poor airflow from the vents. I did the evap core cleaning and it did not help. I have digital climate control. I noticed that with the A/C on I get an excessive amount of air flow from the bottom vent behind the center console. It is almost as if the A/C is on bi-level but it isn't. I took off the piece of plastic behind the center console on the floor to investigate. I noticed one big vent hole I can reach up into and this is where the air is coming from. When I turn on the heater I get all the airflow from this area. I know there is a TSB related to changing the exhaust vent gaskets but this involves a lot of time and requires dismantling the entire dash and I'm not even sure this is my problem. Is there some vent door that is not opening/closing when it should? Has this happened to anyone else? Are there any further ways to troubleshoot this before I commit to removing the entire dashboard?

Does the temperature display on the climate control unit blink?

No...it does not blink and it indicates that all the air is flowing from the upper vents when the A/C is on.

Sounds like a vacuum leak. Have you recently done any engine work? If so, you may have knocked off the vacuum supply hose from the vacuum reservior to the left of the brake master cylinder. It has two vacuum lines leading to it. Make sure they are both there.

Both vacuum lines are present and properly attached.

Many times the vacuum leak will cause the air to come out only the defrost and floor vents... In your case I might suspect problems with the dampers inside the ducts, possibly a buildup of dirt or poor operation and seals.