In emailing Noctua I found out the FC-1 will not control the fan speed at High Speed - it will slow the fan, and stop it (if the no-stop button is not pushed) - but the controller will not run the fans at 2000 RPM.  Noctua writes.. after several emails: "Right now everything heavily suggests that the problem is the motherboard. Our products defect rate is very low, and they are very reliable. Hence, why we offer a 6-year warranty. You are using a Dell system with an OEM motherboard. These motherboards often cause undefined behavior since they don't follow any specifications. ​So, what you are experiencing seems to be normal and what seems to happen is that the motherboard does not supply enough voltage for the fan to spin at its full rated RPM."  If others using the 8940 and the FC-1 have this working I'd sure like to know. Scott  
Yes, lots of posts on Noctua fans and the FC-1 (controller). I've replaced the 2 standard fans in the 8940 with the Noctua fans - like many have. All working fine, connected to the MB fan headers. I wanted to try the FC-1 thinking that I would be able to increase the fan speed to my desired RPM and then forget it. That's still the plan but here's my question: I have both lights on the controller on (green and orange). I have the CPU fan connected to the controller (only), not the exhaust fan. I have no BIOS errors. In controlling the CPU cooler fan, I was expecting some indication that the fan was really running fast if I turned it up all the way with the controller. The controller is up as high as it will go and the fan doesn't appear to be spinning very fast. I can push the NO STOP button and turn knob to stop the fan, so it seems the potentiometer (speed control knob) is working and the orange light dims as I turn the knob counter-clockwise - but I was just expecting a much louder, higher speed, on the CPU fan when the knob was turned up full (full clockwise). The knob should control the pulse width to the fan and as the duty cycle gets near 100%, the fan should be spinning very fast. Now, maybe it is, but I can't hear it and I don't notice tons of air coming from it - so I assume it's not spinning that fast. Yes, I have the power connected to the SATA cable.  Thoughts?.. thanks 
XPS 8940, Noctua NA-FC1, connected, fan speed seems slow