One good thing owning three 9k's (at one time four) is I can swap parts from one car to another. The downside is I cannot always tell you why even if it worked. I am telling you from my experience with my 94 cs turbo, wife's daily ride.
At the start of the heating season last year she complained there was no heat. She can control the fan speed but there was no heat. I was busy with my auto to 5 speed conversion on the 94cde and had no time. So I simply push the rod on the flap so she gets nothing but heat. This went on until in December when I wrecked my 94cs n/a, at which time I removed the fan speed control on the 94 cs n/a to install on her 94 cs turbo.
Problem solved. The ACC went back to normal again, heat or AC. Her 94 cs turbo still has the fan speed control from my wrecked 94 cs n/a.
I can only say the fan speed control is also involved in the decision making of the flap movement together with the ACC. The details are too complicated for my simple head. I am just happy to have the AC and heat working. I'll let someone wiser to decipher what is going on.