How To Test And Replace The Run Capacitor On A Central AC That Isn't Running

Posted on: 3 May 2016

Has your central air conditioner's condensing unit suddenly stopped running without any clear cause? If you have already checked to make sure the breaker or fuses haven't popped and that the thermostat is set correctly, the problem could be a failed run capacitor.

A capacitor is essentially a tiny helper part that carries an electrical charge. The run capacitor carries a charge to help ensure the compressor, which pumps out the gas refrigerant that cools the system, has a steady supply of electricity. A failed capacitor won't give the compressor the electrical boost it needs and the system can then stop running.

You can test the run capacitor for functionality using a multi-meter and replace the part yourself, if necessary. Remember to use caution because the capacitor does store electricity even once the breaker is off. If the idea of working near electricity worries you, call in an air conditioning repair service to perform the task.

Things You Need:

  • Socket wrench
  • Insulated screwdriver
  • Multi-meter
  • New run capacitor, if needed

Step 1: Discharge the Run Capacitor

Turn off the electrical supply to the condensing unit by pulling out the fuses in the fuse box located on the wall near the unit. If you don't have a fuse box, simply turn off the power at the main circuit breaker.

Locate the access panel door on the exterior of your condensing unit. Remove the fasteners with either a screwdriver or socket wrench, depending on the type of fasteners. Pull off the panel door and set the door aside somewhere out of the way but accessible for later.

Find the run capacitor inside using your owner's manual for help, if needed. Note that there might also be a start capacitor inside so you want to make sure you are working on the right capacitor. Do not touch the run capacitor until you have discharged the electricity inside.

Place the end of the insulated screwdriver flat over the top of both terminals on the run capacitor. Hold the insulated screwdriver in place for a long moment or two to discharge the electricity. Now you can proceed to unhooking the wires from the terminals.

Step 2: Test the Run Capacitor for Ohms

Set your multi-meter to the Ohms reading setting. Attach the probes for the meter to each of the terminals on the run capacitor. Make sure the returned Ohms figure matches the Ohms range printed directly on the side of the capacitor. If the numbers don't' match, or no reading shows up at all, you need to proceed with replacing the run capacitor.

Unhook the probe wires and set the meter aside before continuing.

Step 3: Replace the Run Capacitor

Use a screwdriver to loosen the mounting screws on the retaining bracket that supports the capacitor. Pull the capacitor up to free the capacitor from the bracket then discard the capacitor.

Place the new capacitor in the retaining bracket. Secure the bracket screws. Attach the capacitor wires to the right terminals.

Put the access panel door back on the condensing unit then secure with the door's fasteners. Restore the electricity to the unit then turn on your interior thermostat to see if the unit kicks on. If you still don't' have a running air conditioner, call in an HVAC tech like for help.


Working with an HVAC Contractor to Care for Your System

As a homeowner, you know how important your HVAC system is for comfort throughout the year. If the air conditioner or heater is not working properly, it can result in higher energy costs as the system struggles to keep your home temperatures in a comfortable range. Working with an HVAC contractor will help you maintain your system for reliable use long term, and possibly help you cut your power bills enough to notice the savings at the end of the year. Check out the pages on this website to learn more about how to find the perfect HVAC contractor to work with and how you can be of assistance to them when it comes to keeping your system in tip-top shape.