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Everything You Need to Know about Capacitors

Capacitors are an essential component of HVAC systems that help to start up and maintain the motor and compressor. As the system cycles on and off, the capacitor stores and releases electricity to ensure proper functioning. There are various types of capacitors used in HVAC systems, including single run capacitors, dual run capacitors, hard start kits, and soft start capacitors. We will go over each of these types of capacitors in detail and provide you with useful information that can help you select the right capacitor for your system! 

What exactly is a Capacitor

A capacitor is like a battery that helps to start up the Motor and/or Compressor because it takes a bit more energy than just the home electricity. As your Unit cycles on and off the Capacitor is also in use storing and releasing electricity. When replacing a motor that uses a capacitor it is a good idea to also replace the capacitor so there is less chance of having to do so in the future. A bad or old capacitor can damage a new motor or compressor.

Single Run Capacitor

Single run capacitors are commonly used for indoor blower motors, and they come in both round and oval shapes. They typically have a single microfarad rating and two terminals on top, which do not have specific polarities. You will also find that some large roof top units on the condenser side that have multiple fan motors will use single run capacitors for the motors as opposed to a dual run capacitor for the motor and compressor. The last place you may find these are in very old condensing units. They will have a single run capacitor for the fan motor listed and another single run capacitor (with a higher MFD rating) for the compressor.

Most people have moved away from having two separate capacitors to having one dual run capacitor as it cuts down on costs and space when building the units. 

Some single run capacitors will have a voltage of 370 and some will say 370-440. Most manufacturers are moving away from 370V and moving to 440V as it has better durability and longer life span. You can always use a 440 in a 370 application as you can go up in voltage but not down.

Most motors will tell you what capacitor is required on the motor tag: 



Dual Run Capacitors

Dual run capacitors are essential components of outdoor units, heat pumps, and condensers. They have two microfarad ratings—one for the fan motor and one for the compressor—and three terminals that must be hooked up according to their polarity. Understanding how to select and install the correct dual run capacitor is crucial for optimal system performance.

  • C = Common
  • Fan = Fan Motor
  • Herm = Compressor (Hermetic compressor)

Most dual run capacitors will be round, there are some that are oval but they are not really common. To be able to determine the correct dual run capacitor for a unit we will need the model number to find the parts breakdown:



Hard Start Kit - Start Capacitor

A hard start kit, also known as a start capacitor, is an accessory that helps to store energy and assist the compressor and fan motor during startup. This is crucial because HVAC systems require a significant amount of energy to start up, and without a hard start kit, this can put a strain on the system and the house's electrical system. A Start Capacitor is not the same as a single or dual run capacitor. Hard start kit stores energy and uses it to help the compressor and fan motor initially start up where as the single and dual run capacitors help to keep them running after start up.

Example: when your air conditioner starts up in the summer and your lights in the house dim for a second. The hard start kit will help take that load off the houses electrical system and keep your lights from dimming.

These will have a range of microfarads that they work in and also different voltages. Kits will come sometimes with a relay included.

These are most often considered an accessory or aftermarket item and most times will show up in a parts breakdown.

Soft Start Capacitor 

A soft start capacitor works similarly to a hard start kit, but instead of sending the full voltage to the unit to jumpstart it, the soft start capacitor reduces the in-rush current by up to 60% and slowly starts up the compressor. This not only minimizes any damage that can be caused by the jolt of voltage but also reduces the size of the generator needed to start the system by up to 60%, making them a popular option for RVs and other systems that use generators.

Capacitors play a critical role in the operation of HVAC systems. Choosing the right capacitor for your system is important to ensure optimal performance and avoid damage to your motor or compressor. Whether you need a single run capacitor, dual run capacitor, hard start kit, or soft start capacitor, understanding the differences between each type can help you make an informed decision. By following the guidelines outlined in this post, you can keep your HVAC system running smoothly and efficiently. If you need any help, contact our Parts Department, we'd be happy to assist you! 

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