amdx wrote:

that looks like a linear semiconductor controller - an incredibly
antiquated concept for a modern car.

well, you live and learn. apparently the reason they use a linear
controller is because it allows the fan to run near silently at low
speed. with pwm control the fluctuating magnetic fields in the motor
coils cause it to vibrate and make a humming noise at the pwm control
frequency.

that doesn't of course get around the fact that the unit in question
here is apparently badly under rated, but the above does at least
explain why it's used.

I see many Motor Speed Control Manufacturers upped their PWM frequency
to be between 16 K to 22 K to eliminate much of the noise.
Mikek
Sure, if you don't mind heating the motor up...

Jamie