In order to make an AC unit more energy efficient, engineers will try to reduce energy consumption. For example, a fan requires more electricity to start than to continue running once in motion. Thus, if you use a motor that is strong enough to start your fan, you are wasting electricity running the motor once it starts. Engineers will use a capacitor to store electricity while the fan is running. This capacitor can then be used to give a quick burst of electricity to start your fan. Unfortunately, if your capacitor goes bad, it can cripple your system. 

Recognizing Capacitor Problems

Because it is exposed to high heat outside, the capacitor to your condenser fan is the most likely to go bad. When it does, the fan to your condenser unit will not start. Without the current of air your fan creates, your condenser coils will be unable to cool the refrigerant coming from the evaporator unit in your house, and the fan to your evaporator unit will blow warm air into your home. If you stand by a vent and feel warm air coming from it, go outside and check the fan on your condenser unit. If it is not moving, you have a problem with your capacitor.

Troubleshooting a Blown Capacitor

If you have some experience with electronics, you can remove the top of your condenser unit, locate the blown capacitor, remove, and replace it. A capacitor will look like a tiny soda can, and a blown capacitor will be discolored and will have bulges in it. Once you have removed the damaged capacitor, take it to an electrical supply store so they can see what size and capacity it is and then give you a replacement. If you don't feel comfortable working on your own AC unit, you'll need to call an air conditioning repair technician for help. 

A capacitor is a small but essential component of the modern AC unit. At the very least, you can confirm on your own that you have a blown capacitor and pass that information on to your repair professional. While you are waiting for repairs, you can stick a long stem screwdriver into your condenser unit, put the bottom of the screwdriver against the fan blade, and flick your wrist to give your fan motor the push it needs to get started. This will at least get cool air flowing into your house, so you can stay somewhat comfortable while you wait for repairs.