If you're a new homeowner and your air conditioning system trips the circuit breaker, stops working or makes strange humming sounds, you may not know where to look for the problem. One of the things you can do is check the outdoor condenser unit's dual capacitor for problems. The dual capacitor, or start/run capacitor, is a small electrical device needed by most air conditioners to help fan motors and compressor motors start up and remain running without any power fluctuations. Sometimes, capacitors experience problems that interfere with one or all of its functions. Here are more things to know about a start/run capacitor and how you can see if the part has issues to replace or repair.

What Happens When the Capacitor Has Problems?

A bad capacitor may not have enough voltages or power to help the compressor turn on properly when you turn on your cooling system. The lack of power may cause the compressor to operate poorly, or the part may make a humming or buzzing sound as it tries to start up. If the compressor continues to struggle to come on, it may trip the circuit breaker.

The fan may also show signs of struggling by spinning very slowly or not at all. If the compressor does manage to come on when the fan's off, it can overheat. The fan is designed to keep the outdoor condenser unit cool, including the compressor. If the compressor fails, you may need to replace it or the unit itself.

To avoid the expensive problems above, check the capacitor to see it's damaged.

How Do You Check and Troubleshoot the Capacitor?

Before you do anything to the outdoor unit, cut the AC system's power off at the circuit breaker and at the power box located outside the house. The power box usually sits right near the unit. Simply pull the fuses out of the box and set them on a dry surface. Now, locate the capacitor.

The capacitor looks similar to a silver soda or beer can and sits securely behind the corner paneling of your unit. Use a screwdriver to remove the paneling to reveal the capacitor but don't touch it or its wires yet. You want to discharge the capacitor of any electrical currents it may still have running through it with an insulated screwdriver to avoid harming you or anyone in the vicinity. 

On the very top of the dual capacitor sits three distinct terminals with colorful wiring attached to them. The wires connect the terminals to a relay device that leads to the fan and compressor. Holding the screwdriver by its insulated handle only, touch or lay the metal end of the tool across all three terminals to discharge the capacitor. Use a non-contact tester to ensure that the capacitor is discharged. The tester should produce a light or make noise if picks up any electrical currents. If at any time you feel uncomfortable with the process, stop and contact an air conditioning specialist to check the capacitor for you.

If you wish to proceed, use the end of the screwdriver to check the electrical connectors to see if they came loose from the terminals, which may cause problems with the unit. Use insulated pliers to reposition the connectors on their terminals. You can see if this solves your problem by turning the air conditioning system's power back.

You want to see three things happen:

  1. The fan spins fast and smoothly
  2. The compressor motor comes on quietly without stalling or tripping the circuit breaker
  3. The house feels cool and comfortable

If none of the things above occur in a reasonable amount of time, contact an HVAC contractor, such as those at Wright Total Indoor Comfort, to replace it and to check the rest of the condenser unit. The capacitor may have caused additional problems with the fan and compressor.