How to use a salvaged brushless motor
Based on the datasheet, it seems to me the /DEC pin needs to be high (in addition to /ACC being low) for the motor to start. Anywhere between 2.2V and 5V seems fine for /DEC to register as high. Leaving it open-circuit won't do that though.

The reason why it does nothing with no voltage to /DEC is that this chip it has internal pull-down. Possibly other chips of this kind have internal pull-up instead.



And don't apply 24V, you'll fry it. The top limit voltage is given by the VREG pin (which you could measure, but 5V seems safe).