The temp sensor control is a simple thermistor arrangement as I understand it, implying that fan speed vary with the temp of the air flow that goes through the fan when connected to a fan header that supplies constant 12V.
Naturally, I can only guess about the design of the original fan due to lack of documentation but this seems consistent with observations during my attempts to get the supplied fan to work.
I can see no use whatsoever for a crude thermistor-based fan speed control in a cpu cooler for a high powered system where intelligent fan control is almost mandatory.
A possibly complicating factor:
on my MB (asus a8n sli) there are only three-pin fan headers: ground, voltage and rpm sensing. Maybe that can partly explain my problems getting the supplied fan to do what I expected it to. As I said, no fan speed regulating utilities could control the fan speed of the supplied fan.
The pins on four-pin fans are supposed to be used in a way that doesn't seem entirely backwards compatble with three-pin fan headers: http://www.andigilog.com/newsp...%20vs%20DC%20fan3.pdf
Especially not if a temp sensor is included in the circuit.
It would be really nice if one of the AMD technicians could butt into one on the numerous threads on the subject of overheating Opterons and explain how the stock cooler was designed to prevent it.