Start vs Run Capacitors: What’s the Difference?

Not all air conditioning system capacitors are the same. There are different types of capacitors in air conditioning systems, including start and run. If either of them fail, you could be left with an uncomfortably hot home during the summer. Start and run capacitors provide an initial jolt of electricity so that your air conditioning system can cool your home.

What Is a Start Capacitor?

A start capacitor is a device that’s designed to store and supply electricity to an air conditioning system so that it will turn on. Air conditioning systems are powered by electricity. Your home’s electrical system, however, may struggle to provide a sufficient amount of electricity during startup. Therefore, a start capacitor will help to power up your air conditioning system.

What Is a Run Capacitor?

A run capacitor is a device that stores and supplies the necessary electricity to keep the fan motor running. Most air conditioning systems have a single start capacitor and a single run capacitor. Alternatively, they may have a dual capacitor that functions as both a start and run capacitor.

Run capacitors are designed to maintain the charge needed to keep air conditioning systems running. Your air conditioning system will switch from the start capacitor to the run capacitor after it turns on.

Differences Between Start and Run Capacitors

Start and run capacitors are energy-storing devices. They store electricity in conductors, which they supply to air conditioning systems. What’s the difference between start and run capacitors?

Start capacitors operate before run capacitors. Your air conditioning system will require electricity from a start capacitor to begin its cooling cycle. The start capacitor will provide a jolt of electricity so that your air conditioning system’s electrical components – blower fan, condenser fan, compressor, etc. – will turn on.

Run capacitors operate after start capacitors. Your air conditioning system will draw electricity from the run capacitor after it turns on. It will use the start capacitor, after which your air conditioning system will use the run capacitor.

Capacitor Failure: What You Should Know

Capacitors can fail. They are one of the most common parts of a typical residential air conditioning system, in fact, that needs to be replaced. If your air conditioning system has a bad capacitor, it may not turn on. Alternatively, it may turn off unexpectedly or experience poor cooling performance.

While you can’t always prevent capacitors from failing, you can get them replaced. Swapping out a bad capacitor with a new capacitor will restore your air conditioning system.