A window air conditioner has been unplugged from the wall and the technician is about to work around its start and run capacitors. What has to happen before those terminals are touched?
Correct Answer
B) The capacitors must be discharged through a resistor, since they hold a charge unplugged
A capacitor stores energy and keeps storing it after the appliance is disconnected. On a window unit or a refrigerator the stored charge is enough to give a violent shock, and it can persist for a long time because a failed bleed resistor is one of the reasons the capacitor was suspected in the first place. The correct procedure is to short the terminals through a resistor, using an insulated tool, before anything else is touched. Shorting with a bare screwdriver works but welds the tip and destroys the capacitor, so it is a last resort rather than the method.
Why This Is the Correct Answer
Capacitors retain a stored charge after power is removed, and nothing about unplugging the appliance drains them. Discharging deliberately through a resistor bleeds that energy away in a controlled manner without the arc flash and pitting that a direct short produces. It takes a few seconds and it is done before any terminal or wire on the capacitor is handled.
Why the Other Options Are Wrong
Option A: The unit must be plugged in briefly so the capacitors can bleed off through the motor
Reapplying power to bleed a capacitor puts the technician back into a live circuit and does not reliably drain anything once the unit is switched off again.
Option C: The capacitors must be left overnight, which is the only reliable way to drain them
Time is not a reliable discharge method. Many capacitors have no bleed resistor at all, or a failed one, and can hold a dangerous charge for a very long time.
Option D: The capacitors must be taken out of their brackets and stored terminal side down
Removing a charged capacitor means handling it by the case with live terminals exposed, which is more hazardous than discharging it in place.
Memory Technique
Pulling the plug stops the supply. It does not empty the tank.
Reference Hint
Capacitors hold a charge after the appliance is unplugged. Discharge them through a resistor before touching the terminals.
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