What is a Capacitor and Why Do They Break on Air Conditioners?

Living in the desert presents many challenges, but none are as difficult to overcome as the intense heat of the summer. Fortunately, modern air conditioners are constructed with just a few parts, which makes them incredibly reliable.

You can count on your AC unit to keep trucking for years with very little maintenance, but if your air conditioner suddenly refuses to start up one day despite your best care, the capacitor is probably to blame. Though small, capacitors play a big role in your air conditioner’s daily functioning.

What is a Capacitor?

A capacitor is a clever device composed of two metal conductors separated by an insulating material. On an air conditioner, they often look like large, cylindrical batteries with two or three posts sticking out of the top.

The main job of capacitors is to store electrons to provide start-up energy for your air conditioner. When electricity runs through them, they build up a charge by swapping electrons between the two conductive plates inside.

Because of their capacitors, air conditioners do a little magic trick every time they start up. Your A/C unit requires a great deal more start-up energy than is available through your home’s wiring, so the capacitor is added to the circuit to give an electrical jumpstart when the system draws power from the electrical grid. Together, these two electrical sources provide the right amount of juice to your air conditioner. The capacitor’s job is over until an air conditioning cycle is complete. Then the compressor must start up again.

Your air conditioner may contain several different capacitors, including the compressor motor run capacitor, the outside fan motor run capacitor, the indoor fan motor run capacitor and the start capacitor. The most common to fail is the compressor motor run capacitor. It has a big job and an even bigger footprint on your AC system since it’s a dual capacitor with three terminals instead of just two.

Why Good Capacitors Go Bad

Capacitors fail often—they do a tough job, and their work takes a toll. A few factors play heavily into the lifespan of AC capacitors, including:

• Heat exposure. In Phoenix, heat may be one of the most damaging elements for air conditioner capacitors. Unfortunately, exposing these units to high heat for extended periods greatly shortens their lives and can cause significant damage to your unit. Make sure you shade your air conditioner. Keep it clean and the air circulating to maximize your capacitor’s lifespan.
• Voltage rating. All capacitors have a voltage rating, which informs air conditioner technicians exactly which capacitor matches which air conditioner. Unfortunately, homeowners may try to cut costs by replacing the AC capacitors themselves without understanding how to choose the right one. An undersized capacitor won’t hurt your air conditioner but will significantly shorten the capacitor’s life. If you decide to DIY this job, remember that bigger is better. If your air conditioning system is a 370-volt unit, bumping up to a 400-volt capacitor will ensure you get enough power and that your capacitor comes closer to reaching its maximum life span.
• Age. Like all things, capacitors have a limited life span. Most are designed to last approximately 20 years, but several factors can cause them to wear out more quickly. Suppose your air conditioner cycles much more rapidly than average. In that case, your capacitor is undersized (as mentioned above) or built from problematic parts, and the estimated life span may be greatly reduced. Fortunately, these parts are relatively inexpensive to have replaced, so even if your capacitor wears out before your air conditioner does, it won’t break the bank.

How to Know If Your AC Needs a New Capacitor

Below are some telltale signs indicating you have a defective AC capacitor and tips on addressing this issue to restore your cooling system’s performance:

• Your air conditioner is not blowing cold air. Try resetting your system by turning it off and on again. If the issue persists, it may indicate a faulty capacitor or other malfunction requiring professional attention. Contact a qualified technician to diagnose and repair the problem for optimal cooling performance.
• High energy bills. A defective capacitor can cause your air conditioning unit to work harder than necessary to cool your home, increasing electricity consumption and higher utility costs.
• Humming noise. If you hear a humming sound or your AC takes minutes to start, you likely have a failing AC capacitor.
• Your HVAC system is old. Over time, wear and tear can take a toll on your AC unit, leading to performance issues and component failures. Consider contacting a technician to inspect your system and recommend a capacitor replacement if necessary.
• Your AC will turn off on its own. A problematic capacitor can cause your air conditioning system to cycle on and off repeatedly, disrupting its performance and efficiency.
• AC won’t turn on immediately or won’t turn on at all. Suppose you’re experiencing long delays or a complete lack of response when powering your air conditioner. In that case, it’s time to have your capacitor inspected and potentially replaced by a professional technician.

How to Manage AC Capacitor Problems

If you have a problem with your AC capacitor, it is recommended that you have a skilled and qualified HVAC professional to diagnose and fix it. However, you can do a few things to manage capacitor issues until a professional arrives.

• Turn off the power. Before troubleshooting an AC capacitor problem, turn off your unit’s power first to ensure safety from injuries or electrical shocks.
• Check for any sign of damage. Examine your capacitor and look for any visible signs of bulges or cracks. If you see any damage, ensure you replace the capacitor immediately.
• Test your capacitor. Use a multimeter to test if the AC capacitor is working accordingly. If it has lost its capacitance, you need to have it replaced.
• Clean your AC unit. Debris and dust can accumulate on the capacitor, reducing its efficiency and causing damage in the long run. Ensure your unit is cleaned regularly to prevent similar problems.
• Schedule routine maintenance. Regular maintenance by a skilled HVAC professional can help keep AC capacitor problems at bay. Routine maintenance can also help identify and address issues before they require costly repair or replacement.

Keep Your AC Running with a Healthy Capacitor

A capacitor is a crucial component of your air conditioning system. If you suspect your AC’s capacitor is malfunctioning, having it inspected and replaced as soon as possible is important to prevent further damage and ensure efficient operation.

If your air conditioner is refusing to start, running with little enthusiasm, making weird noises, or just isn’t cooling right, call Precision Air. Our technicians are NATE certified and trained to handle any problem your air conditioner can throw at them. Remember, we don’t charge weekend fees or add trip charges to your bill; we’ll come out when it’s convenient for you. A quick call to 602-349-6922 is all it takes to schedule your appointment, 24 hours a day, seven days a week!