How to test electric motor capacitors

Written by daniel ray
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How to test electric motor capacitors
Learn to test the electric capacitor before operating your air conditioner. (Jupiterimages/Comstock/Getty Images)

Testing the starting capacitor on a motor is a good first step to getting a motor to run. If the capacitor turns out to be defective, you'll need to replace it.

Skill level:
Moderately Easy

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Things you need

  • Ohm meter
  • Screwdriver

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  1. 1

    Disconnect power to the electric motor. Locate the motor's starting capacitor. It's often mounted to the motor case.

  2. 2

    Inspect the capacitor. If the capacitor is leaking, it is considered bad and must be replaced. Make sure the wiring is correctly connected and isn't damaged. If damage is found, repair the wiring or replace the capacitor.

  3. 3

    Use a screwdriver to short the two capacitor leads. Disconnect the capacitor and remove it.

  4. 4

    Set the ohm meter to a high resistance range, at least "x100." Connect the meter leads to the capacitor leads. Once the leads are connected, the meter needle should move toward the low, or "0 ohm," side of the scale. Next, slowly move toward the high, or infinity, side of the scale.

  5. 5

    If the capacitor does not test as described above, short out the capacitor leads one more time in case residual voltage is in the capacitor. Retest the capacitor with the meter. Replace the capacitor if it fails the test again.

Tips and warnings

  • If possible, consult a schematic of the motor circuit to help with your troubleshooting.
  • To prevent electrical shock, always make sure that power is removed from the motor.

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