Capacitor Problem on an Air Conditioner

Capacitor Symptoms

• Your air conditioner will show a few different symptoms that may indicate a bad capacitor. If your outdoor condensing unit’s fan will not operate, it could be the motor capacitor for that fan. The indoor blower motor will stop working if the indoor capacitor is faulty. In addition the compressor on your air conditioner, which is necessary for creating cold air by compressing the refrigerant, will not function if its capacitor has gone bad. If you physically inspect the capacitor, you may see that the part itself, generally a cylindrical component, is swollen and oil may have leaked out of the part. This is a sure sign the capacitor needs replacement.

Testing

• You can test your air conditioner’s capacitors by using a standard multimeter. Connect the probes on the meter to the terminals on the capacitor to check for the proper level of microfarads – the standard for measuring its storage capacity. This rating is generally listed as a certain number of MFD/uf or microfarads. In a run capacitor, you connect a probe to each of the terminals and set your meter to the “MFD” setting. See if the reading is close to the MFD/uf rating on the capacitor. If it’s close, then the capacitor works. If it’s not close, then you need to replace it.

Replacing the Capacitor

• Replacing a capacitor is not difficult and since generally you can't repair a bad capacitor, replacement is the best option. Turn off the service switch to your outside unit and turn off any breakers assigned to the air conditioning system. You may wish to confirm that there is no power to the unit using your voltage meter. You’ll have to remove the main panel of the outside unit to reach the capacitor. This is usually the panel marked with a voltage warning sticker. Find the cylinder and locate the wires connected to the top of it. You will need to disconnect the wires and connect them to the new capacitor using the proper terminals for each wire. The terminals are typically marked “C,” “Fan” and “Herm” on a dual-run capacitor. These labels stand for “common,” “fan” and “compressor” respectively. A single-run capacitor will only have two of the three. Make sure the wires go back on the correct terminals on the new capacitor and put it back in the place where the old one was stored. The new one may not look exactly like the old one, but it should have comparable storage ratings. Replace the panel and turn the power back on.

If Air Still Runs

• Just because your capacitor is bad doesn’t mean you will see the obvious symptoms. You may have to test it if you suspect a problem, because the compressor or fans may run regardless in some cases. The problem with ignoring a bad capacitor is that a weak capacitor will make the motor or compressor run more amps and use much more electricity. The system will run hot and the life expectancy of your air conditioner will likely be shortened.