How to Diagnose an Air Conditioner Capacitor Problem

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How to Test Your Air Conditioner Capacitor

Are you having air conditioning problems in your home and suspect it may be an air conditioner capacitor problem? Below I have laid out a step-by-step guide on how to test your AC capacitor to see if it is good or if you have a capacitor problem.

First – before I go any further I need to lay out this disclaimer! WARNING – This procedure involves a risk of shock – do not attempt this unless you are familiar with high-voltage safety.

Ok, here are the tools you will need:

  • Screw Driver with an insulated handle
  • Insulated Gloves
  • Meter with micro farads or meter with resistance (ohms)

Steps:IMG_20130722_135348_123[1]

  1. If you are unfamiliar with high voltage in your outdoor unit, do not attempt this procedure!!!!!
  2. Remove the disconnect or turn off the circuit breaker this should turn off the 240 volts to the outside unit
  3. Turn your thermostat down below room temperature and select cooling (this will still send 24 volts to the outside unit but the 240 volts required to run the compressor and fan should be off from the disconnect or circuit breaker)
  4. Check that the outdoor unit is not running (you will hear a hum but the unit is not running)
  5. Turn thermostat to OFF (this will turn off the 24 volts to unit and the humming will stop)
  6. Remove the panel covering the electrical components
  7. Put on your insulated gloves
  8. Get your screwdriver with an insulated handle
  9. Take the screwdriver and touch both the “C” (common) connection and the “HERM” (compressor) tabs on the top of the capacitor to discharge the HERM side of the capacitor.
  10. Take the screwdriver and touch both the “FAN” and the “C” common tabs on the top of the capacitor to discharge the FAN side of the capacitor
  11. Make a note which wire is connected to which terminal (ex. Brown to Fan, red to C, Purple to C, Yellow to HERM) each brand of system may vary slightly, so write down the terminal-wire connection
  12. Remove the wires from the capacitor
  13. (opt1) Take the leads from the meter, with the meter set on micro-farads and check the reading with one lead on C and the other on either the HERM or FAN tabs
  14. (opt1) if the reading is in the operating range written on the side of the capacitor then the capacitor is good
  15. (opt2) with the meter set on ohms, check the reading with one lead on C and the other on either the HERM or FAN tabs
  16. (opt2) watch the reading rise from zero (0) to its max and then fall back to zero (you are charging and discharging the capacitor on the resistance setting) if the maximum reading is in the operating specification on the side of the capacitor, then the capacitor is good.
  17. Replace the wires exactly as they were taken off in step 9 using your notes
  18. Replace the electrical cover on the unit
  19. Replace the electrical disconnect

Always call an experienced HVAC professional to check your capacitor.

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About Author

Frank Alexander is an experienced engineering professional who holds a Master of Engineering degree from North Carolina State University and an MBA from the University of South Carolina.

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