Designing Heating and Cooling Systems in Large Buildings
About Me
Designing Heating and Cooling Systems in Large Buildings

Have you ever wondered what goes into a heating or air conditioning system for a large office building or another large building like a mall or a school? My name is Evelyn, and I am an HVAC architect. I design heating and air conditioning systems for large, corporate buildings. Making sure that a large building with many rooms or offices is efficiently heated and cooled is a very large job and is much more complicated than simply heating or cooling a home. This blog will educate the reader on how heating and cooling jobs this large are designed and completed.


Designing Heating and Cooling Systems in Large Buildings

Why Are AC Run Capacitors Such Common Failure Points?

Nicole Jacobs

Central air conditioning systems can fail for many reasons, ranging from relatively minor to catastrophically expensive. Like any sophisticated mechanical system, many air conditioner failures result simply from normal wear and tear and usage. The run and start capacitors are two common failure points that can affect even relatively "young" air conditioners.

Fortunately, replacing a capacitor usually isn't an expensive or time-consuming job, but what causes them to fail in the first place? Keep reading to learn a little more about why your system's run capacitor may be failing and what you can do to prevent additional failures in the future.

Understanding Your Air Conditioner's Capacitors

If you didn't take an introductory electronics class in school, you might not be too familiar with the concept of capacitors or capacitance. Like batteries, capacitors store energy. Unlike batteries, they don't use a chemical reaction for storage and instead utilize electric fields to maintain a voltage potential.  All residential air conditioning systems contain two capacitors: a run capacitor and a start capacitor.

Your AC's run capacitor helps to ensure a smooth flow of current. Imagine you have a mechanical water pump that occasionally turns on and off. If you store the water from the pump in a tank, you can get a smooth flow without worrying about interruptions from the pump. The run capacitor serves a similar role — it stores energy and then releases it as a smooth and consistent current.

The run capacitor is a critical part of your AC system, and it helps protect expensive components such as your compressor from inconsistent power levels. A faulty run capacitor may cause your system to shut down suddenly, run poorly, or produce noticeable and disturbing vibrations and noises.

Common Causes of Run Capacitor Failure

Capacitors are incredibly simple electronic components, and they'll typically only fail for three reasons:

  • Heat
  • Excessive voltage
  • Age

You'll rarely see voltage high enough to damage your air conditioner's run capacitor outside of specific situations, such as a nearby lightning strike causing a transient. In most cases, run capacitors fail due to age or heat exposure. Most capacitors should last the system's life under ideal conditions, but yours may fail if your air conditioner is particularly old.

Heat is a more common cause of failure. High ambient temperatures can, over time, reduce the lifetime of a capacitor. As a result, your run capacitor may fail long before the rest of your system wears out. Likewise, other problems with your AC system that cause it to short cycle can work the capacitor harder, causing its temperature to increase and reducing its lifespan.

In general, replacing a run capacitor once during your system's life is not a cause for concern. If you are frequently replacing these components, you should rely on a service technician to determine if your system is suffering from excessive voltage or heat build-up. Reach out to a professional if you need air conditioning repair services.