[tucsonjwt]

Here are some things I have experienced with my 83 C20:

Make sure that all of the air ducts are seated in their adjoining duct (one slips into the other). My ducts have often been dislodged somewhat and that messes up the airflow. Start from the center air box below the dash and go from there.

I like the air to blow directly on me, not the floor, so make sure that the ducts going to the outboard dash vanes and the center vane are intact. I got some HVAC shinny silver tape (not duct tape) and taped the duct joints to seal them and prevent air loss under the dash. It is a real pain to get these ducts in place and stay there, especially the outside vanes and the center vane. I had to remove the dash to do mine right. Also, make sure that the air hose going from the center under dash distribution box to the right side dash vane is in place - you can remove the glove box and get at this somewhat.

I close the passenger side dash vane and point the other dash vanes at my face.

If you do these things you should get about the same amount out of the bottom as the top (for the driver's side).

When I had my square bodies converted to 134 from R12, I noticed a significant drop in cooling - still cool but not like R12. With the R12, the A/C cooled so much that the defects I described above didn't seem to make much difference. Of course, it is 115 degrees in the shade in the Arizona desert, so we notice marginal cooling right away.

I know this duct sealing is a pain, but I found it was worth the effort. Good luck.