How to Test Fan Motor Starting Capacitors

Problems with motors may actually be within the start capacitor rather than the fan motor itself. Many motors use start capacitors to regulate the electrical components of the motor during the start process. Testing the start capacitor before you throw away the motor saves the expense of purchasing another motor as compared to the cost of replacing the start capacitor. Replacing the capacitor usually doesn't require calling a professional electrician.

Things You'll Need

  • Phillips screwdriver
  • Slotted screwdriver
  • Analog volt meter
  • Safety glasses
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Instructions

    • 1

      Disconnect the wires that supply power to the motor with appropriate screwdrivers. Let the wires that run from the capacitor to the motor connected for the time being.

    • 2

      Switch the analog volt meter from ohms to volts. Create a parallel circuit by placing the leads on the meter onto the wires of the capacitor. Hold these leads until the reading from the voltage meter is zero.

    • 3

      Disconnect the wires that run from the capacitor to the motor. Switch the volt meter to the ohm setting. Place the leads of the ohm meter on the wires that run from the capacitor to the motor. Count to three while the leads on the meter charge the capacitor. Reverse the leads on the capacitor. Look for movement of the needle on the meter toward infinite ohms. If the meter doesn't move toward infinite ohms, the capacitor is bad.

    • 4

      Look for movement of the needle on the meter toward infinite ohms. Repeat this step three times. Replace the capacitor if this step fails at any time.

Tips & Warnings

  • Safety glasses should be free of dust and debris to protect your eyes during the testing and changing of the capacitor while at the same time preventing vision from becoming obstructed.

  • Observe all electrical codes when working with any electrical wiring.

  • Shorting the capacitor across the terminals could cause an explosion.

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References

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