I have searched for an answer to this problem since last year. The local repair shops are unsure of any fixes, so i thought i would put it out here on the forum.
I have a 94 325i convertible, with a dual ac system (different temp settings for passenger and driver). It is the analog (dial) system. When I place the air flow indicator on the footwell setting, air comes out toward the feet and toward the windshield (defrost). The trouble is that the air coming out of the passenger side is at full heat, no matter where the temp is set. If I use the dash setting for airflow, the temp is right. I assume there must be a mixing valve or ?, but i have no idea where to look. One shop said it required taking the entire dash apart to get to it, but even then, they were not sure that this would fix the problem.
Any ideas or suggestions will be greatly appreciated.