Thanks very much for the reply. The bottom return isn't blocked for sure. I can see my fingertip through it.
But I wondered about a blockage in the freezer. I had the ice maker motor out to check the evap motor to see with my own eyes that it was working. What could block it. Or, alternatively, the blockage could be the closed damper. Any harm if I prop it open to see if that cools the refrig side?