What Does an AC Capacitor Do?

When it comes to AC breakdowns, one of the most common causes is a faulty AC capacitor. Capacitors are an essential part of every air conditioner’s electrical system. For this reason, we recommend checking your capacitor when your air conditioner is giving you trouble. But before you attempt to fix an AC capacitor, it’s best you know the answer to, “what does an AC capacitor do?”

AC capacitors are small cylindrical objects that can store energy (in other words: a short-term battery). They send electrical signals that power the motors and in turn the rest of the unit. There are multiple capacitors within a given AC unit. For instance, there are “start” capacitors (which send signals to start up the motor), and “run” capacitors that regularly send signals to keep the motor running. Typically, there is a capacitor assigned to each compressor, outside fan, and blower motor.

There are multiple capacitors within a given AC unit. For instance, there are “start” capacitors (which send signals to start up the motor), and “run” capacitors that regularly send signals to keep the motor running. Typically, there is a capacitor assigned to each compressor, outside fan, and blower motor.

How to Diagnose an AC Capacitor Problem

When your AC capacitor is failing, you’ll likely be able to diagnose it yourself. If you hear your unit humming but the fan is not running, the capacitor is likely the culprit. This happens most often during the summer when the hot weather combined with the heat of the motor generates more wear-and-tear on the capacitors.

There is a test to help you verify this. Take a long, skinny stick and gently push one of the fan blades to see if it will spin. If it does and it keeps going, you likely have a failing “start” capacitor. That capacitor isn’t supplying enough power to set the cogs of the wheel in motion, so to speak.

How to Repair an AC Capacitor

If you’re up for a DIY start capacitor repair, give these instructions a look:

1. Disconnect power at either the disconnect or breaker panel: This is important! You’ll risk injury otherwise. If you’re unsure of how to do this, don’t process with this repair.

2. Locate your capacitor: Remove the service panel off of your AC unit and locate your start capacitor. Here’s an example of what yours will likely look like:

AC Capacitor

3. Discharging the capacitor’s power: For this step, proceed with caution! Even though you’ve turned off the power to the unit, there’s still power contained within the capacitor. For this reason, never touch the terminals with your bare hands. Your capacitor will need to be discharged. Watch this video closely to know how (Courtesy of Richard Lloyd/YouTube):

After the capacitor has been discharged, dismount the capacitor. You’ll likely have to remove a screw from a metal band.

4. Make note of how its wires connect: This is important to do before disconnecting the wires, as it’ll make the installation of the new one significantly easier. We suggest taking a picture of them, so you have it for reference.

5. Disconnect the old capacitor: With needle-nose pliers, use a slow rocking motion to pull the wires from the old capacitor.

6. Install new capacitor: The most important things to keep in mind when looking for a new capacitor are the micro-farads and the voltage rating. The size doesn’t have to be identical to your previous capacitor.

Note: If you live in the Tampa Bay, FL area stop by Appliance & A/C Parts Today. We carry a large inventory of A/C appliance parts, including capacitors. Contact us today!