Upon my search of the mixer door the only read was to remove the entire dash but I gave it a look, and found this may be true for a proper fix, but I have no one to impress, but myself, and found a way to shift the mixer door from heat to AC with a flick of my finger, by reaching under the dash where the passenger foot vent is, and moving the linkage aprox 1.5"

I thought I would add some photos to help out the next guy.

pschoggens

 

Cool.......I know the 5th gens (94-97) "have issues" with those cables.....I check/adjust mine twice a year - the manual calls this a Blend Door Adjustment.

Going into summer to be sure I get MAX AC performance. Then again in the fall so I can get MAX Heat.......I'm to the point I don't even put that cover back on, who is going to be looking at the underside of the dash from that pass seat besides me?