How do you know if start capacitor de-energized after start up?

You can determine if a start capacitor has de-energized after startup by checking for a voltage drop across the capacitor terminals using a multimeter. If the voltage is close to zero or significantly lower than the rated voltage after the motor has started, the capacitor has likely de-energized. Additionally, some systems have built-in indicators or relays that disconnect the capacitor once the motor reaches a certain speed. Lastly, a visual inspection for signs of overheating or damage can also indicate proper function.