Start Capacitors vs Run Capacitors: What’s the Difference?

One of the most common reasons why an air conditioner stops working is a failed capacitor. In an air conditioning system, the capacitor is the energy storage device that holds the electrical charge needed to power the fan motor. Therefore, the failure of the capacitor means that your air conditioning system will stop blowing cold air, and a replacement is required.

The Two Types of Capacitors

There are two types of capacitors: run capacitors and start capacitors. Run capacitors are more common. They store the energy that is needed to keep the fan motor going so that the air conditioner continues to cool down your house. In contrast, the start capacitor specifically provides the energy needed to start up your air conditioner. As you might expect, it takes more torque to start the motor than to keep it running, so the capacitance — that is, the energy storage capacity  — of a start capacitor must be higher than that of a run capacitor. To understand why, think about the fan motor like a push-powered merry-go-round on a playground — it can take considerable effort to get it started, but once it gets going, you don’t need to push as much to keep it running. Therefore, the capacitance rating for most run capacitors is between 5 and 80 Microfarads (MFD), while it typically ranges from 430 MFD to 516 MFD for start capacitors.

Deciding What to Do When Your Capacitor Gives Out

When the capacitor in your AC system gives out, you are faced with a decision: Should you replace the capacitor or replace the entire system? That may depend on whether the problem is with the start capacitor or the run capacitor. If the problem is with the run capacitor, replacing the capacitor often makes more sense. Depending on the MFD, the price of a run capacitor can range between less than 10 and 100 dollars, so it’s a safe investment. In most cases, replacing your run capacitor can get your system back up and running in no time!

However, if the problem is with the start capacitor, you may want to consider replacing the system altogether. Start capacitors are larger and more expensive, and they are a lot harder to find, since most AC systems today do not have a separate start capacitor. If your system is getting old and its parts are giving out, it may be time to consider an upgrade.

 
Whether you are looking for a replacement run capacitor, a new AC system, or any other HVAC equipment, National Air Warehouse can help you find what you need. Contact us today to learn more about all of our products!