What cap value to use for window “box” fan?
I presume torque and speed are max at one value and reduced at others?

Increasing the capacitor value above the &quot;correct&quot; capacitor value, may result in increasing the torque and speed but the incremental speed increase will decline. Make sure that the current drawn does not exceed the rating marked on the fan. Lower capacitor values result is less speed and torque. Below some minimum capacitor value, the fan will not have enough torque to start and the speed may vary a lot.