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HVAC Capacitor Size Chart

Published by HVACProSales Team on Mar 16th 2026

Quick Answer Box

What size capacitor do I need for my HVAC unit?

The correct HVAC capacitor size (measured in microfarads, MFD or µF) is determined by the compressor and fan motor specifications. A 2-ton AC typically uses a 35/5 MFD dual-run capacitor, a 3-ton uses a 40/5 MFD, and a 5-ton unit often requires a 60/5 MFD capacitor. Always verify the exact size on the unit’s data plate or the old capacitor’s label.

As an HVAC technician, you know that a failed capacitor is one of the most common reasons for an AC or heat pump to stop working. Replacing it is a quick fix, but only if you have the right part. Using the wrong size capacitor can lead to premature motor failure, increased energy consumption, and a callback from an unhappy customer.

This guide provides a comprehensive HVAC capacitor size chart and explains the critical factors to ensure you select the correct replacement every time.

How to Read HVAC Capacitor Ratings

Before consulting the chart, it’s essential to understand the information printed on the capacitor itself. You will typically find two key ratings:

  1. Microfarad (MFD or µF): This is the capacitance rating and the most critical value. It indicates the capacitor’s ability to store an electrical charge. On dual-run capacitors, you will see two numbers, such as 40/5 MFD. The larger number is for the compressor motor, and the smaller one is for the condenser fan motor.
  2. Voltage: This rating indicates the maximum voltage the capacitor can safely handle. A common rating is 370/440 VAC. When replacing a capacitor, you can use one with the same or a higher voltage rating, but never a lower one.

Diagram showing how to read HVAC capacitor ratings A diagram illustrating where to find the MFD and Voltage ratings on a standard dual-run HVAC capacitor.

HVAC Capacitor Size Chart by AC Tonnage

While the most reliable method is to check the specifications on the unit or the old part, this chart provides common capacitor sizes for standard residential AC and heat pump condensing units.

| AC Unit Size (Tons) | BTU | Common Dual-Run Capacitor Size (MFD/µF) | | :--- | :--- | :--- | | 1.5 Ton | 18,000 | 30/5 MFD | | 2 Ton | 24,000 | 35/5 MFD | | 2.5 Ton | 30,000 | 40/5 MFD | | 3 Ton | 36,000 | 40/7.5 MFD or 45/5 MFD | | 3.5 Ton | 42,000 | 45/5 MFD or 50/5 MFD | | 4 Ton | 48,000 | 50/7.5 MFD or 55/5 MFD | | 5 Ton | 60,000 | 60/5 MFD or 70/5 MFD |

Disclaimer: This chart is for reference only. Always confirm the required capacitor size with the manufacturer's specifications for the specific unit you are servicing.

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Verifying Capacitor Size with a Multimeter

If the capacitor’s label is worn off or unreadable, you can use a multimeter with a capacitance setting to determine the correct MFD rating.

  1. Disconnect all power to the HVAC unit.
  2. Safely discharge the capacitor by shorting the terminals with an insulated screwdriver.
  3. Set your multimeter to the capacitance (µF) setting.
  4. Measure the capacitance between the HERM (compressor) and C (common) terminals, and between the FAN and C terminals.

The readings should be within +/- 6% of the rated MFD. If they are outside this range, the capacitor needs to be replaced.

HVAC technician using a multimeter to test a capacitor An HVAC technician uses a multimeter to safely test the microfarad rating of a dual-run capacitor.

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Expert Summary: Key Takeaways for Technicians

  • Always Match MFD: The microfarad (MFD) rating must match the original equipment specifications.
  • Voltage Can Be Higher: You can replace a capacitor with one of a higher voltage rating, but never lower.
  • Dual-Run vs. Single-Run: Understand the difference and use the correct type. This guide focuses on dual-run capacitors, the most common type in residential units.
  • Check for Physical Damage: A bulging, leaking, or cracked capacitor is a clear sign of failure.
  • When in Doubt, Verify: Use the unit’s data plate or a multimeter to confirm the correct capacitor size.

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FAQ Section

Q: Can I use a 40/5 MFD capacitor instead of a 35/5 MFD? A: No. Using a capacitor with a higher MFD rating than specified can cause the motor to overheat and fail prematurely. Always use the exact MFD rating.

Q: What does the +/- 6% tolerance mean? A: This indicates the acceptable range for the capacitor's actual capacitance compared to its rated value. A capacitor rated at 40 MFD is acceptable if it measures between 37.6 and 42.4 MFD.

Q: Does the brand of the capacitor matter? A: While OEM capacitors are always a safe bet, a quality aftermarket capacitor with the same MFD and voltage ratings will work correctly. Focus on quality brands known for reliability.

Blog Tags: * HVAC Repair * HVAC Tools * HVAC Capacitors * Troubleshooting * HVAC Parts