Heater & A/C control

The earlier mechanical over vacuum push buttons jambed, broke, failed to provide defrost or heat so the user beat the button assembly to death.
Blend doors get hard to move with age and tempature change. Most to the point a cable cant move it the full travel let alone a vacuum servo. Hope this explains why the later is a combination of both vacuum and mechanical doors, thus better. I do like the look of the lighted push buttons.