I use a Mitsubishi fan controller from a Legnum VR-4 on my Link ECU. The fan controller "fails safe" - if the PWM signal fails (such as with a loose connection), the fan comes on at 100%. The more Duty Cycle, the slower the fan goes - with 100% being fully off. I am actually running mine at 20Hz, and that seems to actually work OK for me - not sure what impact it would have being driven at a higher frequency?   Here's an example of my PWM output table. As I have a chargecoole