How To Test Capacitor On Ac Unit With Multimeter

5 min read Jun 26, 2024
How To Test Capacitor On Ac Unit With Multimeter

Testing a Capacitor on an AC Unit with a Multimeter: A Step-by-Step Guide

Why Test a Capacitor on an AC Unit?

A capacitor is a crucial component in an AC unit, responsible for storing energy and providing a boost to the compressor and fan motors. A faulty capacitor can cause a range of issues, including reduced airflow, increased energy consumption, and even complete system failure. Testing the capacitor regularly can help identify potential problems before they become major issues.

What You'll Need

  • A multimeter (digital or analog)
  • The AC unit's capacitor
  • The capacitor's specifications (voltage and capacitance ratings)

Step 1: Prepare the Multimeter

Set the Multimeter to the Capacitance Mode

  • Switch the multimeter to the capacitance mode (usually denoted by the "C" or "μF" symbol).
  • Ensure the multimeter is set to the correct range for the capacitor's capacitance rating.

Step 2: Disconnect the Capacitor

Shut Off the AC Unit

  • Make sure the AC unit is powered off before attempting to test the capacitor.
  • Verify the unit is completely shut down before proceeding.

Disconnect the Capacitor

  • Locate the capacitor and disconnect it from the AC unit's electrical circuit.
  • Take note of the capacitor's polarity (if applicable).

Step 3: Test the Capacitor

Measure the Capacitance

  • Connect the multimeter's leads to the capacitor's terminals (following the multimeter's instructions).
  • Take a reading of the capacitance value in microfarads (μF).

Compare the Reading to the Specification

  • Check the capacitor's specification sheet or manufacturer's documentation for the rated capacitance value.
  • Compare the reading from the multimeter to the specified value.

What to Look For

  • A reading significantly lower than the specified value may indicate a faulty capacitor.
  • A reading significantly higher than the specified value may indicate a capacitor that is about to fail.
  • A reading close to the specified value indicates a functional capacitor.

Additional Tests

Leakage Test

  • Set the multimeter to the ohms (Ω) mode.
  • Measure the resistance between the capacitor's terminals and the surrounding metal casing.
  • A reading close to infinity (open circuit) indicates a good capacitor. A low reading may indicate a faulty capacitor.

ESR (Equivalent Series Resistance) Test

  • Use a multimeter with an ESR function or a dedicated ESR meter.
  • Measure the ESR value according to the multimeter's instructions.
  • A high ESR value may indicate a faulty capacitor.


Testing a capacitor on an AC unit with a multimeter is a relatively simple process. By following these steps, you can identify potential issues with the capacitor and take corrective action to ensure the AC unit operates efficiently and effectively. Remember to always follow proper safety precautions when working with electrical systems, and consult a professional if you're unsure about any aspect of the testing process.

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