You cannot replace the digital climate control with the analog unit without replacing the whole heater box, which requires taking apart half the interior. Total headache... To me, it sounds like your CC head unit (control module) is dead, and it isn't just a fuse or final stage unit. I'd look at replacing it with a used unit.
1998 BMW 328is
1966 Pontiac GTO
2007 Subaru Impreza 2.5i 5-door
View my photos: Caught in the Wild