Test Ac Run Capacitor With Digital Multimeter

6 min read Jun 26, 2024
Test Ac Run Capacitor With Digital Multimeter

Testing an AC Run Capacitor with a Digital Multimeter


AC run capacitors are an essential component in many electrical circuits, including air conditioners, refrigerators, and pumps. They help to improve the efficiency and performance of the motor by providing a boost to the starting torque. However, like any other component, AC run capacitors can fail, and when they do, it can cause the motor to malfunction or not start at all. In this article, we will discuss how to test an AC run capacitor with a digital multimeter.

What is an AC Run Capacitor?

Before we dive into the testing process, let's quickly understand what an AC run capacitor is. An AC run capacitor is a type of capacitor that is designed to provide a high voltage and high current to the motor windings during startup. It helps to improve the power factor of the motor and reduce the current drawn from the power supply.

Why Test an AC Run Capacitor?

Testing an AC run capacitor is crucial to ensure that it is functioning properly. A faulty capacitor can cause a range of problems, including:

  • Motor overheating: A faulty capacitor can cause the motor to overheat, leading to premature failure.
  • Reduced motor efficiency: A faulty capacitor can reduce the motor's efficiency, leading to increased energy consumption and higher electricity bills.
  • Motor failure: In severe cases, a faulty capacitor can cause the motor to fail completely, leading to costly repairs or even replacement.

Tools Required

To test an AC run capacitor, you will need the following tools:

  • Digital multimeter: A digital multimeter is a versatile tool that can measure voltage, current, resistance, and capacitance.
  • Capacitor tester (optional): A capacitor tester is a specialized tool that is designed specifically for testing capacitors.

Testing an AC Run Capacitor with a Digital Multimeter

Step 1: Disconnect the Power Supply

Before testing the capacitor, make sure to disconnect the power supply to the motor. This is an essential safety precaution to avoid any accidental starts or electrical shocks.

Step 2: Identify the Capacitor Terminals

Identify the terminals of the AC run capacitor. Typically, the terminals are marked as "C" for the common terminal and "F" for the fan terminal.

Step 3: Set the Multimeter to Capacitance Mode

Set the digital multimeter to capacitance mode (usually denoted by the "C" or "Cap" symbol).

Step 4: Connect the Multimeter Leads

Connect the multimeter leads to the capacitor terminals. Make sure to connect the leads correctly, with the positive lead connected to the "C" terminal and the negative lead connected to the "F" terminal.

Step 5: Take the Reading

Take the capacitance reading on the multimeter. The reading should be close to the rated capacitance value of the capacitor.

Step 6: Check for Leakage

Check for any leakage in the capacitor by setting the multimeter to ohms (Ω) mode. A good capacitor should show a high resistance reading (usually in the megaohms range).

Step 7: Check the Capacitor Voltage Rating

Check the voltage rating of the capacitor using the multimeter. The voltage reading should be close to the rated voltage of the capacitor.

Interpreting the Results

If the capacitance reading is significantly lower than the rated value, it may indicate a faulty capacitor. Similarly, if the leakage reading is low or the voltage rating is not within the specified range, it may indicate a faulty capacitor.


Testing an AC run capacitor with a digital multimeter is a relatively simple process that can help you identify any faults or issues with the capacitor. By following the steps outlined in this article, you can ensure that your motor is running efficiently and safely. Remember to always follow safety precautions when working with electrical circuits, and if you are unsure about any aspect of the testing process, it is always recommended to consult a qualified electrician.

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