How To Check Ac Capacitor With Multimeter

5 min read Jun 26, 2024
How To Check Ac Capacitor With Multimeter

How to Check an AC Capacitor with a Multimeter

A capacitor is an essential component in many electrical circuits, including air conditioning systems. Over time, capacitors can deteriorate or become damaged, leading to system failures or inefficient operation. In this article, we will guide you on how to check an AC capacitor with a multimeter, a simple and effective method to ensure your capacitor is functioning properly.

Why Check an AC Capacitor?

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

  • System Efficiency: A faulty capacitor can reduce the overall efficiency of your air conditioning system, leading to increased energy bills and reduced cooling performance.
  • System Failure: A damaged capacitor can cause system failure, resulting in costly repairs and downtime.
  • Safety: A malfunctioning capacitor can pose a safety risk, as it can lead to electrical shocks or even fires.

Tools Required

To check an AC capacitor with a multimeter, you'll need the following tools:

  • A digital multimeter (set to capacitance measurement mode)
  • The AC capacitor to be tested
  • A pair of test leads (optional)

Step-by-Step Guide

1. Disconnect Power

Before starting the test, ensure the power supply to the capacitor is disconnected. This is crucial to avoid any electrical shock or injury.

2. Identify the Capacitor

Locate the AC capacitor in your air conditioning system. It's usually a cylindrical or rectangular component with two terminals.

3. Set the Multimeter

Set your digital multimeter to capacitance measurement mode (usually denoted by the symbol "C" or "Cap"). Consult your multimeter's user manual if you're unsure.

4. Connect the Test Leads (Optional)

If your multimeter has test leads, connect them to the capacitor terminals. Ensure the leads are securely attached to prevent any electrical shock.

5. Take Readings

Touch the multimeter's probes to the capacitor terminals. The multimeter will display the capacitance value in microfarads (μF). Take note of the reading.

6. Compare with Manufacturer's Specifications

Compare the measured capacitance value with the manufacturer's specifications, usually found on the capacitor's label or in the system's documentation. A significant deviation from the specified value indicates a faulty capacitor.

7. Perform a Simple Inspection

Visually inspect the capacitor for signs of damage, such as:

  • Swelling or bulging
  • Leaks or cracks
  • Burn marks or discoloration
  • Loose or corroded terminals

Any signs of physical damage or wear indicate a faulty capacitor.

Interpreting the Results

  • If the measured capacitance value is within the specified tolerance, the capacitor is likely functioning properly.
  • If the measured value is significantly lower than the specified value, the capacitor may be faulty or deteriorated.
  • If the measured value is significantly higher than the specified value, the capacitor may be faulty or damaged.


Checking an AC capacitor with a multimeter is a simple and effective way to ensure your air conditioning system operates efficiently and safely. By following these steps, you can identify faulty capacitors and replace them before they cause system failures or safety hazards. Remember to always disconnect power supply before starting the test and exercise caution when handling electrical components.