Hello, you don't mention which floorplan View you have, but it's pretty irrelevant since the ceiling plan is near the same across all Views/Navions. The factory just bores a hole in the foam-molded plenum for wherever a diffuser is supposed to go. You should have a ceiling diffuser just behind the forward facing vent for the overhead cab. Does that diffuser blow air? If so, it could be a blocked or partially blocked plenum to that vent. It is easy to check for obstruction by removing the vent grill.
If the diffuser mentioned above doesn't have airflow, then the problem is likely at the fan plenum. This requires removal of the interior A/C filter, trim, and A/C metal plenum plate. Once in that plenum, it is easy to see the "port" and "starboard" plenums that run front to back in the ceiling. Check each plenum opening with a light. You are primarily interested in the "port" (drivers) side. Look for loose/lodge foam chunks within the plenum. You can place a flashlight in the vent that serves the overhead. You should see the light at the fan plenum or even at the diffuser drop behind that vent.
Good luck!
B~
