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What You Should Know about Air Conditioning Start-Run Capacitors

There are many reasons why an air conditioner won’t cool, but some causes are more common than others.

One such common problem is the failure of your air conditioner’s start-run capacitor.

This component is integral to the functioning of a central air conditioning system, and if it stops working, your air conditioner will not produce cold air.

Below is more information about the start-run capacitor, including its function and how you can know if your system’s start-run capacitor has failed.

How Air Conditioners Utilize Compressors for Cooling

Air conditioners are somewhat complex pieces of equipment, but their overall function is elegant and simple.

In fact, all air conditioners work by transferring heat from interior air to the atmosphere outside.

No matter the system size or specific design, air conditioners convert hot, and often humid, air into cool, dry air that is much more comfortable for occupants.

To accomplish this task, air conditioners utilize refrigerants, such as the name-brand compound Freon, which are special chemicals that absorb heat from the passing air. A refrigerant passes through the air conditioner in an endless loop and continually absorbs, then releases heat in a never-ending cycle.

To make heat absorption a possibility, a refrigerant must first be pressurized within the air conditioner, and the system’s compressor is key to this happening. This heavy-duty component is located in the outside unit of the air conditioner and is powerful enough to convert the refrigerant gas into a liquid.

Undoubtedly, air conditioning compressors are strong, but they also require a lot of energy to get started and to keep running.

Conventional household electric current lacks the necessary power to get the compressor started, so a booster in the form of a start-run capacitor is needed.

How the Start-Run Capacitor Works

The start-run capacitor functions like all capacitors do by holding an electrical charge until needed.

Capacitors are fairly simple components that store electricity in a similar manner to batteries, however, unlike batteries, capacitors release their charge in a sudden surge of energy when needed.

Capacitors can maintain voltage that well-exceeds the typical current found in a residential setting. For example, a start-run capacitor may output hundreds of volts of alternating current (AC).

In the case of the start-run capacitor, the accumulated electrical charge enters the compressor motor upon start-up and during operation, which provides sufficient energy to overcome the substantial inertia that keeps the compressor at-rest, and provides extra power so the compressor can run efficiently.

What Happens When a Start-Run Capacitor Fails

A start-run capacitor undergoes countless cycles of charging and discharging, and the cumulative effects of handling large voltages can cause the unit to fail.

Failure may be more likely during hotter times of the year, as hot external temperatures can stress the capacitor.

If the start-run capacitor fails:

  • It may swell or burst open
  • The compressor will no longer operate
  • The interior unit may still function and cause the blower fan to activate, but the passing air will not be cooled
  • The inside fan will continue blowing indefinitely as the indoor temperature will not be lowered

In many cases, it is fairly easy to tell if your air conditioner’s start-run capacitor has failed:

  • If the indoor blower continues to run a lengthy period of time with no discernible temperature drops, then you should suspect a bad start-run capacitor is the source of trouble.
  • There is a complete absence of noise while standing next to the outdoor unit – in some cases, an audible humming noise can be heard, but no other activity is visible

Can a start-run capacitor be replaced?

Fortunately, replacing a start-run capacitor isn’t difficult for trained personnel. However, the potential for serious electrical shock is a big reason that this job should be left up to the professionals.

Our Air  Conditioning Repair experts can replace your start-run capacitor and can get your air conditioner up and running, and your home cool again in no time.

Simply Contact Us at (651) 294-7798 today and tell us how we can help you.

Schedule a HVAC repair anywhere in the Minneapolis or St. Paul area today by calling (651) 294-7798 or by requesting an estimate online.


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