One idea to check if the vacuum system checks out.
Once the engine is shut off, the vacuum bleeds down and the HVAC defaults to defrost. On quite a few cars I've discovered the foam seal on the diverter flap has degraded, leaving the sticky glue to effectively glue the door shut. If you are lucky, you might be able to pull out the center vents and pry open the door with a small flat file or dental pick. I ended up inserting a temperature probe in the vent to prevent the door from closing, I haven't gotten the energy to pull the dash apart to do a proper fix.