HVAC Run & Start Capacitors

Find the exact replacement capacitor for your AC, heat pump, or furnace. Look up by equipment model number or shop by specs — every order ships same day before 3 PM CST.

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MFD Rating check your old cap

How to Choose the Right HVAC Capacitor

Every air conditioner and heat pump uses capacitors to start and run the compressor and fan motors. A run capacitor stays in the circuit continuously to keep the motor efficient and running smoothly. A start capacitor provides the burst of torque needed to get the compressor spinning during startup, then disconnects once the motor reaches operating speed.

Understanding MFD Ratings

The MFD (microfarad) rating is the most important specification when choosing a replacement capacitor. Dual run capacitors show two values like 35+5 MFD, where the larger number powers the compressor and the smaller number powers the fan motor. Single run capacitors show one value like 45 MFD. Always match the MFD rating exactly to your old capacitor, as the wrong rating can damage your compressor or cause it to overheat.

Voltage Ratings: 370V vs 440V

HVAC capacitors come in 370V and 440V ratings. A 440V capacitor can safely replace a 370V unit because the voltage rating is a maximum, not an exact requirement. However, a 370V capacitor should never be used to replace a 440V unit. At National HVAC Parts, most of our universal capacitors are rated 370/440V for maximum compatibility.

OEM vs Universal Capacitors

OEM capacitors are manufactured for specific equipment models and carry the original brand name. Universal capacitors are built to the same electrical specifications but fit a wide range of HVAC systems. Both types deliver the same performance when the MFD and voltage ratings match. Universal capacitors from National HVAC Parts are UL-listed, feature oil-filled construction, and carry our fitment guarantee.

Signs Your Capacitor Needs Replacement

Common symptoms of a failing capacitor include: AC hums but the compressor will not start, outdoor fan spins slowly or not at all, system short-cycles on and off, higher than normal electricity bills, or a visibly swollen, bulging, or leaking capacitor. If you notice any of these signs, replacing the capacitor promptly can prevent more expensive compressor damage.

Finding Your Replacement

Check the label on your existing capacitor for the MFD rating and voltage. Use our Look Up by Model Number tool above to find the exact OEM replacement for your unit, or use Shop by Specs to browse by MFD size. Every order placed before 3 PM CST ships same day from National HVAC Parts.

Frequently Asked Questions

Can I use a 440V capacitor to replace a 370V?

Yes. The voltage rating on a capacitor is a maximum, not an exact requirement. A 440V capacitor can safely replace a 370V unit with the same MFD rating. However, a 370V capacitor should never be used to replace a 440V unit, as it may fail from overvoltage. Most universal capacitors at National HVAC Parts are rated 370/440V for maximum compatibility.

What does a dual MFD rating like 35+5 mean?

A dual run capacitor has two capacitors in one housing. The larger number (35 MFD) powers the compressor motor and the smaller number (5 MFD) powers the condenser fan motor. Both values must match your existing capacitor exactly. Using the wrong MFD can cause motors to overheat, run inefficiently, or fail to start.

Where do I find my equipment model number?

The model number is printed on the equipment data plate, usually a silver or white metal tag attached to the unit. For condensing units, check the access panel on the side. For furnaces, check inside the blower compartment door. The model number typically starts with letters followed by numbers, like 24ACC636A003 or PG9MAA024060AEKA.

Are universal capacitors as reliable as OEM?

Yes. Universal capacitors are built to the same electrical specifications and UL safety standards as OEM parts. When the MFD and voltage ratings match, performance is identical. Universal capacitors from National HVAC Parts are oil-filled for longer life and carry our fitment guarantee. The only difference is the brand label on the housing.

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