How To Check A Start Capacitor With A Digital Multimeter

6 min read Jun 26, 2024
How To Check A Start Capacitor With A Digital Multimeter

How to Check a Start Capacitor with a Digital Multimeter

A start capacitor is a crucial component in many electrical devices, including air conditioners, refrigerators, and washing machines. Its primary function is to provide a high-voltage electrical burst to start the motor, ensuring a smooth operation. However, like any other component, start capacitors can fail, leading to motor malfunction or even complete failure. In this article, we will guide you on how to check a start capacitor with a digital multimeter.

Why Check a Start Capacitor?

Before we dive into the checking process, it's essential to understand why checking a start capacitor is crucial:

  • Identify faulty capacitors: A faulty start capacitor can prevent the motor from starting, leading to device malfunction or breakdown.
  • Prevent motor damage: A failing start capacitor can cause the motor to overheat, leading to premature wear and tear, or even complete motor failure.
  • Ensure efficient operation: A healthy start capacitor ensures the motor operates efficiently, reducing energy consumption and prolonging its lifespan.

Tools Required

To check a start capacitor, you'll need the following tools:

  • Digital multimeter: A digital multimeter is an essential tool for measuring electrical parameters, including voltage, current, and capacitance.
  • Multimeter probes: Ensure you have the appropriate multimeter probes for measuring capacitance.
  • Start capacitor: The start capacitor you wish to test.

Step-by-Step Guide

Step 1: Disconnect Power

Before starting the test, ensure the device is disconnected from the power source to prevent any accidental starts or electrical shocks.

Step 2: Identify the Capacitor

Locate the start capacitor in your device. It's usually a cylindrical or oval-shaped component with two or three terminals.

Step 3: Set the Multimeter

Set your digital multimeter to the capacitance measurement function (usually denoted by the "C" or "Cap" symbol). Ensure the multimeter is set to the correct range for the capacitor's rated capacitance value.

Step 4: Connect the Probes

Connect the multimeter probes to the capacitor terminals. For a two-terminal capacitor, connect the probes to the two terminals. For a three-terminal capacitor, connect the probes to the two outer terminals.

Step 5: Take Readings

Take note of the capacitance reading on the multimeter display. A healthy start capacitor should read close to its rated capacitance value, usually indicated on the capacitor casing or in the device's documentation.

Step 6: Check for Leakage

To check for leakage, set the multimeter to the ohms (Ω) function. Connect the probes to the capacitor terminals, and take a reading. A healthy start capacitor should show infinite ohms or a very high resistance value (>10MΩ). Any reading below this indicates leakage or a faulty capacitor.

Step 7: Verify the Capacitor's Integrity

Perform a visual inspection of the capacitor for signs of physical damage, such as cracks, bulges, or rust. A damaged capacitor is likely to be faulty and should be replaced.

Interpreting the Results

  • Capacitance reading close to rated value: The start capacitor is likely healthy and functioning correctly.
  • Capacitance reading significantly lower than rated value: The start capacitor is likely faulty and should be replaced.
  • Leakage or low resistance reading: The start capacitor is likely faulty and should be replaced.


Checking a start capacitor with a digital multimeter is a relatively simple process that can help you identify faulty capacitors and prevent motor damage. By following these steps, you can ensure your devices operate efficiently and prolong their lifespan. Remember to always follow safety precautions when working with electrical devices and to consult a professional if you're unsure about the testing process.

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