I had the same problem last year.. but I heard the servo motor turning (takes about 20 secs to turn all the way). I then started troubleshooting with the help of some members on this board, and it turned out to be the microswitch inside the assembly. I replaced that and my fans (footwell blowers) came on right away.. and voila.. toasty toes!
Question for '86 911 Turbo owners: footwell fan operation