How To Test A Motor Start Capacitor? EASY GUIDE

A motor start capacitor is an essential part of an electrical system. It helps to regulate the flow of electricity, and it also has to be tested regularly to ensure it is functioning correctly. Testing a motor start capacitor is easy but requires specialized equipment. Here’s how to test a motor start capacitor in your home or business. 

How To Test A Motor Start Capacitor | Step By Step Guide 

Things You Will Need

The first step in testing a motor start capacitor is to gather the appropriate tools and materials.

You’ll need a multimeter, which measures voltage, current, and resistance

Make sure that all electrical connections are disconnected before beginning the testing process. Once you have the proper tools, you can start testing the capacitor. 


Step 1: Unplug your motor from the wall outlet before doing anything else. This is an important safety measure that must be noticed. 

Step 2: Locate the capacitor on the motor. It should be cylindrical, with two electrical terminals coming from one end and a rubber cover on the other. The rubber cover will need to be removed to access the terminals. 

Step 3: Use an ohmmeter to measure the resistance between each terminal and the ground (the capacitor’s body). The reading should show infinite resistance—in other words, no connection—between each terminal and the ground. If there is any connection, this indicates a short circuit within the capacitor, and it needs to be replaced. 

Step 4: With your ohmmeter still connected, measure the resistance between each terminal and one another. The reading should be lower than 500 ohms, but not zero or infinity (if it’s either of those, then again, you’ll need to replace the capacitor). If this reading is too high, it could indicate too much capacitance in the system, which can cause excessive current draw when starting up your motor. 

What Are The Indicators If The Capacitor Is Not Working?

Identifying a capacitor that is not working can be tricky. Generally, it is difficult to tell whether a capacitor is broken by looking at it. To accurately diagnose the issue, you need to use an ohmmeter or multimeter. If the component isn’t working correctly, the meter will measure no resistance, which indicates a short circuit in the unit. In this case, it’s been damaged and needs to be replaced. Another possible indicator of non-functioning capacitors is a change in capacitance when tested. Whenever this occurs, it’s inevitable that the component has gone bad and must be replaced for normal operations to resume.

What Causes A Motor Start Capacitor To Fail?

Motor start capacitors are electrical devices that help motors draw a high current when starting. They are commonly used in air conditioners, refrigerators, and other large appliances. While these capacitors can last for many years, they will eventually fail due to wear and tear. Let’s take a closer look at what causes motor start capacitor failure and how it can be prevented. 


The most common cause of motor start capacitor failure is age. Over time, the electrolyte inside the capacitor loses its ability to hold a charge, resulting in the loss of power that enables the motor to run efficiently. This type of wear-and-tear is simply unavoidable; even if you take excellent care of your capacitor, there will come a time when it needs to be replaced due to age alone. 

Corrosion Or Oxidation On The Terminals

Another common cause of motor start capacitor failure is corrosion or oxidation on the terminals or connections. This can occur due to moisture from condensation or exposure to corrosive gasses and liquids such as those found in specific industrial environments. Corrosion can prevent the capacitors from connecting effectively with the circuit board, resulting in reduced performance and eventual failure. 

Overvoltage Or Undervoltage

Finally, one of the most damaging causes of motor start capacitor failure is overvoltage or Undervoltage conditions in the power supply line. Too high or too low voltage can cause arcing or sparks within the capacitor, which damages its internal components and leads to premature failure. It is essential to ensure that your power supply voltage remains within acceptable limits to prevent this catastrophic damage. 

Bottom Line: 

Now you have an idea about how to test a motor start capacitor. Testing your motor start capacitor is a reliable way to determine whether or not any issues are causing the inefficient performance of your motor system. By taking a few simple steps with an ohmmeter, you can quickly diagnose problems with your capacitor so they can be fixed quickly and easily – saving you both time and money! Whether you’re a DIY enthusiast or an experienced professional, this guide will help make testing a breeze so you can get back up and running as soon as possible!