Testing Capacitor On Ac Unit

5 min read Jun 26, 2024
Testing Capacitor On Ac Unit

Testing a Capacitor on an AC Unit


A capacitor is a crucial component in an AC unit, responsible for storing electrical energy and providing power to the compressor and fan motor. When a capacitor fails, the AC unit can malfunction or even stop working altogether. In this article, we will guide you through the steps to test a capacitor on an AC unit.


Before testing the capacitor, make sure to:

  • Turn off the power to the AC unit at the circuit breaker or fuse box.
  • Verify that the AC unit is completely shut down and cool to the touch.
  • Ensure that you are not standing on a conductive surface or wearing any metal objects that could cause electrical shock.

Tools and Materials Needed

  • A digital multimeter (DMM) with a capacitance measurement function
  • A capacitor tester (optional)
  • A wrench or pliers to access the capacitor

Step 1: Locate the Capacitor

The capacitor is usually located in the compressor compartment or near the fan motor of the AC unit. It may be held in place by a bracket or clip. Identify the capacitor and take note of its voltage rating and capacitance value, usually marked on the capacitor itself or on the AC unit's datasheet.

Step 2: Measure the Capacitance

Using a digital multimeter with a capacitance measurement function, set the meter to the capacitance mode (usually denoted by the "C" or "μF" symbol). Touch the multimeter leads to the capacitor terminals, observing the correct polarity (the red lead to the positive terminal and the black lead to the negative terminal). Take note of the measured capacitance value.

Note: If the meter shows an open circuit or infinite resistance, the capacitor is likely faulty.

Step 3: Measure the Capacitor's ESR (Equivalent Series Resistance)

Set the multimeter to the ohms (Ω) mode and measure the ESR across the capacitor terminals. A good capacitor should have a low ESR value, usually less than 1 ohm.

Step 4: Perform a Visual Inspection

Visually inspect the capacitor for signs of physical damage, rust, or corrosion. Check for swelling, bulging, or leaking electrolyte. If you notice any of these signs, the capacitor is likely faulty.

Step 5: Test the Capacitor using a Capacitor Tester (Optional)

If you have a capacitor tester, use it to test the capacitor's capacitance and ESR values. Follow the tester's instructions and compare the results with the manufacturer's specifications.


By following these steps, you can test a capacitor on an AC unit and determine if it's functioning properly. If you find the capacitor to be faulty, replace it with a new one of the same capacitance value and voltage rating. Remember to always turn off the power to the AC unit before attempting any electrical repairs.

Important Safety Reminder: Always exercise caution when working with electrical components, and consider consulting a professional if you're unsure or uncomfortable with the testing process.

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