Home » Guides » How to Test a Run Capacitor With a Multimeter? Guide Of 2023

How to Test a Run Capacitor With a Multimeter? Guide Of 2023

By Arslan Ash

How to test a run capacitor with a multimeter

As an electrical engineer, I love explaining how things like circuits and electronics work. I write on my blog to share simple explanations, reviews, and useful tips about the latest technology.

Various electrical appliances and HVAC systems rely on run capacitors for efficient operation. To help motors start quickly and run smoothly, these small but vital components store and release electrical energy. Run capacitors can deteriorate over time, leading to malfunctions and reduced performance in your appliances. To ensure the optimal functioning of your equipment, it's essential to know how to test a run capacitor with a multimeter. You should first learn about run capacitors, and then move on to testing.

What is a Run Capacitor?

A run capacitor serves a specific purpose in the operation of many electrical devices, and is an essential component. Capacitors are used to store electrical energy temporarily and release it in a controlled manner to assist in starting and running motors. Various appliances rely on them to maintain their efficiency and performance.

What is a Run Capacitor

HVAC (heating, ventilation, and air conditioning) systems, electric motors, and other equipment that depends on motors commonly use run capacitors. Together with the motor, they provide the necessary boost for a smooth startup and ensure steady operation. The role of run capacitors is crucial to diagnosing and resolving issues in these devices, making it a valuable skill for anyone dealing with electrical equipment.

Signs of a Faulty Run Capacitor

Run capacitors are crucial components, but like any part, they can develop issues over time. Recognizing the signs of a faulty run capacitor is vital for prompt diagnosis and repair. Here are the common symptoms to watch out for:

1. Motor Hard Startin

When a run capacitor starts to fail, one of the most noticeable signs is the motor's difficulty in starting. The motor may take longer to kick into action, and you may hear a noticeable hum or buzz as it struggles to get going. This can lead to increased wear and tear on the motor, potentially causing it to fail prematurely if the issue is not addressed.

2. Reduced Motor Performance

A decline in the overall performance of the motor is another indication of a faulty run capacitor. You might observe decreased power output, slower rotation, or even instances where the motor shuts off unexpectedly. These issues can disrupt the operation of the appliance or equipment in which the motor is installed.

3. Overheating

Signs of a Faulty Run Capacitor

Faulty run capacitors can lead to overheating of the motor or the capacitor itself. This can cause safety concerns and may even result in system shutdowns to prevent damage. If you notice excessive heat around the capacitor or the motor, it's a clear signal that something is amiss.

4. Audible Clicking or Hissing Sounds

Sometimes, a damaged run capacitor can produce unusual sounds, such as clicking or hissing. These noises are often due to internal arcing or electrical discharge within the capacitor. They can be an early warning sign that the capacitor is failing and may need replacement to prevent further damage.

5. Motor Humming Without Starting:

faulty sign of bad capacitor

In some cases, a motor may only emit a constant hum without actually starting. This is a strong indicator that the run capacitor is no longer providing the necessary boost for motor operation. It's essential to address this issue promptly to avoid motor damage and further complications.


How to Test a Run Capacitor with a Multimeter?

The test of a run capacitor can now be performed after you know the signs of a faulty run capacitor. The following is a step-by-step guide:

Step# 1: Safety Precautions

Before you start testing a run capacitor with a multimeter, it's crucial to prioritize safety. Ensure that the equipment is disconnected from the power source to prevent electrical shocks. Always wear appropriate personal protective gear, such as insulated gloves and safety glasses, when working on electrical components. Remember, capacitors can hold a charge even when disconnected, so it's essential to discharge them before testing to avoid accidents.

Step# 2: Select the Right Multimeter Setting

how to set multimeter on capacitance mode

Choose the appropriate setting on your multimeter for capacitance measurement. Look for the Greek letter "μ" symbol, which represents microfarads (μF). This is the unit of measurement for capacitance. Set your multimeter to the μF range suitable for the expected capacitance of the run capacitor you are testing. Usually, run capacitors in HVAC systems have capacitance values between 2μF to 80μF. Ensure that your multimeter is functioning correctly and its probes are in good condition.

Step# 3: Discharge the Capacitor

how to discharge a run capacitor

Before testing, discharge the run capacitor to ensure there's no residual charge that could give you an inaccurate reading or potentially shock you. To discharge the capacitor, use a resistor-equipped screwdriver with insulated handles. Simply bridge the terminals of the capacitor with the resistor for a few seconds. This should safely discharge any stored energy.

Step# 4: Locate and Access the run Capacitor

how to locate run capcitor in motor

In most cases, the run capacitor is located within the HVAC unit, often near the fan or compressor. Depending on your equipment, you may need to remove a cover or panel to access it. Make sure to consult the manufacturer's instructions or a wiring diagram if you're unsure about its location. Once accessed, visually inspect the capacitor for any signs of physical damage or leakage before testing.

Step# 5: Testing Procedure

How to test a run capacitor with a multimeter

Using your multimeter, carefully touch one probe to the "C" terminal (common) and the other probe to the "Herm" terminal (hermetic) on the capacitor. Make sure the probes are firmly connected to the terminals. The multimeter will display a capacitance reading in microfarads (μF). Compare this reading to the capacitor's labeled capacitance rating. If the reading is significantly different from the labeled value, it may indicate a faulty capacitor that needs replacement.

Step# 6: Interpret the Results

Good readings have microfarads within 10% of the labeled specification. However, if the reading is significantly lower or higher than the labeled value, it suggests a faulty capacitor that needs replacement. It's crucial to ensure the replacement capacitor has the same capacitance rating, voltage rating, and physical size as the original one.

Step# 7: Measuring Resistance of run capacitor

For a capacitor to be in good health, it must be tested for resistance. Identify if it is good or bad by checking its resistance with a multimeter.

Step# 8: Setting up the Multimeter

how to set multimeter on resistances mode

To begin, switch your multimeter to the "Resistance" or "Ohms" setting. This setting is typically represented by the Ω symbol. Ensure that the multimeter is set to a high resistance range, which usually reads "1K" or "10K" ohms. Setting it to a higher resistance range allows for more accurate readings.

Step# 9: Measuring Resistance with the Multimeter

After setting up the multimeter, discharge the capacitor if you haven't already, and then disconnect the capacitor's wires. Place the multimeter probes on the capacitor terminals. It's important to connect the red probe to the "C" or "COM" (common) terminal on the multimeter and the black probe to the "Ω" or "resistance" terminal. Now, take the reading on the multimeter. A healthy run capacitor should show a low resistance value, which gradually increases as the capacitor charges. If the multimeter shows no change or infinite resistance, it indicates a faulty capacitor.

Step# 10: Interpreting Multimeter Readings

The multimeter reading will provide you with valuable information about the capacitor's health. If the resistance reading starts at zero and gradually increases, it means the capacitor is functioning correctly. However, if the multimeter reads infinite resistance from the start and doesn't change, the capacitor has likely failed. Always cross-check the reading with the manufacturer's specifications to confirm if it falls within the acceptable range.


Tips for Accurate Testing

After knowing how to test a run capacitor with a multimeter, it is important to follow some tips for safely testing it. Here are some tips to ensure precise and reliable testing:

Use a High-Quality Multimeter

Invest in a good-quality multimeter with a reputation for accuracy and reliability. A high-quality multimeter not only provides accurate readings but also ensures safety during the testing process.

Discharge the Capacitor Safely

Always discharge the capacitor before testing it. This eliminates any residual charge, reducing the risk of electrical shocks or damage to the multimeter. Use an appropriate resistor or a specially designed capacitor discharge tool for this purpose.

Follow the Manufacturer's Specifications

Consult the manufacturer's specifications for the run capacitor to determine the expected resistance and capacitance values. This information serves as a reference point to compare your test results and identify any discrepancies.

Temperature Considerations

Keep in mind that temperature can affect capacitance readings. Some capacitors may display variations in capacitance with temperature changes. When possible, perform the test at room temperature or within the specified range for accurate results.

Avoid Handling Capacitors with Bare Hands

To prevent contamination of the capacitor, which can affect readings, avoid touching the terminals with your bare hands. Use clean, dry gloves or a suitable tool when handling capacitors.


Summary

I hope you know now how to test a run capacitor with a multimeter. Take action immediately if you notice any signs of a faulty run capacitor. Safety should be the top priority throughout the process. In testing run capacitor, my additional tips for accurate measurement will be very helpful.