What is a capacitor?

Essentially a capacitor is a battery. It regulates voltage amp and keeps them in check so to speak. Imagine a heartbeat monitor, you see on the monitor the wavy line that is your heartbeat. Electricity is exactly like that and a capacitor puts a line or bar above and below so that the amps cannot go beyond a certain point. This prevents the voltage from putting excess strain on all the electrical parts in your AC. You may also have them in your furnace for your blower motor.
Capacitors are filled with mineral oil and like any other sealed liquid once heated, it turns to gas and the gas expands. This causes a “pop can” effect and weakens your capacitor which can cause a unit not to perform properly or not at all. With most manufacturers only putting a 1 year warranty on capacitors, you can see why it is important to have them checked every year to ensure optimal performance, preventing breakdowns of your ac unit.
Why only a year you may be asking yourself? Well here in Kansas especially, we have crazy weather. It could be 30 in the morning and 100 in the afternoon. With weather like that, this type of part can not keep up with the harshness. Yes, us Kansans are used to it but the US average temperature (for 2017) is 54.54° Fahrenheit, so you can see how 110° or -5 could be harsh (statista.com).
Another cause of failure is over amping. Over amping can be caused by a multitude of things, but in most cases a unit is plugged up from dirt and debris. This causes a lot of strain on your compressor and that in turn will over amp the capacitor and unit. Running an air conditioner with a weak capacitor also causes premature failures and loss of parts such as fan motors and compressors. Most manufacturers tell you compressors are bulletproof. A compressor failure indicates a serious issue or a prolonged period of strain on the compressor. It’s also imperative to have the right size capacitor that and meets the manufacturer specifications.