Here's the pictures I promised on how to disassemble the ACC unit...
remove the temperature unit and the cover off the fan buttons so can remove the buttons by psuhing from behind. Plastic tabs are delicate after 20 years, so careful not to break. Use penknife to slip between plastic tabs so they can be gently popped apart (ie. don't cut the plastic with it). With fan button unit cover removed, pop three fan buttons off from behind.
Pop front loose. One tab on top, two on bottom (circled in blue in previous two pictures). The front can't come off because the buttons hold it on. I couldn't figure out how to pull them off, so I did this in order to...
Reach in behind the front with a penknife so can et behind each button and pop it forward off its switch.