How to Check a HVAC Capacitor


A capacitor is an electrical device used to store power for appliances that need an extra surge of energy to begin working. Commonly found in refrigerators and heating, ventilation and air conditioning equipment, a capacitor is dangerous to work with. Even with the appliance unplugged, the capacitor can still hold an active charge. Touching it while charged can be lethal. Once it's discharged, checking the capacitor to find out whether it's bad is easy.

Things You'll Need

  • Digital multimeter with a capacitance setting
  • Screwdriver
  • Unplug the appliance and open the unit to gain access to the capacitor.

  • Visually check the capacitor. If it bulges, is discolored or leaks fluids, there is no further need for any testing. Replace the capacitor since it is bad and will soon fail.

  • If the capacitor looks OK, then short it out out by holding an insulated screwdriver by the grip and placing the shank across the two terminals. This drains the capacitor of any charge and makes it safe to work with. If you are not sure the capacitor is drained, then short it several times.

  • Disconnect the capacitor from the appliance wires.

  • Set the multimeter on capacitor reading and connect the two leads to the capacitor terminals.

  • Read the meter to determine whether the capacitance is within 6 percent of the rating of the capacitor. The rating is found on the capacitor. If it is within 6 percent, then the capacitor is not bad and is working. There may be other internal problems within the capacitor that will cause future problems, but these require specialized technical equipment to diagnose.

Tips & Warnings

  • The easiest way to handle a capacitor that you suspect is failing is simply to replace it.

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  • Photo Credit Polka Dot Images/Polka Dot/Getty Images
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