Can I replace a dual run capacitor myself?

Yes, if you follow proper safety procedures — specifically discharging the capacitor before handling. Many HVAC technicians and experienced DIYers replace capacitors without professional help.

What does 45+5 MFD mean on a capacitor?

It means the capacitor has two separate ratings: 45 MFD for the compressor circuit (HERM) and 5 MFD for the fan motor circuit (FAN). The "+" separates two values, not digits of one number.

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

Yes. A 440V-rated capacitor is compatible with 370V systems — the voltage rating indicates the maximum the capacitor can handle, not the operating voltage.

How long does a dual run capacitor last?

Typically 10–20 years under normal conditions. Heat and electrical stress accelerate failure — capacitors in hotter climates tend to fail sooner.

Where can I buy a replacement dual run capacitor?

Cooling Parts Supply carries genuine dual run capacitors with verified specs, in stock and ready to ship same day.

How to Replace a Dual Run Capacitor (HVAC Step-by-Step Guide)

A failed dual run capacitor is one of the most common causes of AC system failure — especially during summer heat. The good news: it's one of the most straightforward repairs in HVAC. This guide walks you through how to safely identify, test, and replace a dual run capacitor.

What Is a Dual Run Capacitor?

A dual run capacitor is a single cylindrical component that serves two circuits simultaneously: one for the compressor (HERM terminal) and one for the condenser fan motor (FAN terminal). It's identified by two capacitance values printed on the label — for example, 45+5 MFD — separated by a plus sign. The first number (45 MFD) serves the compressor; the second (5 MFD) serves the fan motor. Both share a common terminal (C/COM).

Signs of a Failed Capacitor

AC unit turns on but fan doesn't spin
System hums but doesn't start
Compressor stutters or short-cycles
Visible bulging or oil leakage on the capacitor body
Multimeter reading outside ±6% of rated MFD

Tools You'll Need

Multimeter with capacitance function
Insulated screwdriver
Needle-nose pliers
Replacement capacitor (matching MFD and voltage rating)

Safety Warning

Capacitors store electrical charge even when power is off. Always disconnect power at the breaker AND discharge the capacitor before touching any terminals. Use an insulated screwdriver to short across the terminals through a resistor or discharge tool — never short directly.

Step-by-Step Replacement

Step 1 — Disconnect Power

Turn off the AC unit at the thermostat and disconnect power at the breaker. Wait at least 5 minutes before opening the unit.

Step 2 — Locate the Capacitor

Open the access panel on the condenser unit (outdoor unit). The dual run capacitor is a cylindrical metal can, usually located near the contactor. It will have 3 terminals on top: HERM, FAN, and COM.

Step 3 — Discharge the Capacitor

Using an insulated screwdriver, carefully short across the HERM-to-COM and FAN-to-COM terminals to discharge any stored charge.

Step 4 — Document the Wiring

Take a photo of the existing wiring before removing any terminals. Note which wire connects to HERM, FAN, and COM.

Step 5 — Test the Old Capacitor (Optional)

Set your multimeter to capacitance mode. Test each section: HERM-to-COM and FAN-to-COM. A reading outside ±6% of the rated MFD confirms the capacitor has failed.

Step 6 — Remove and Replace

Disconnect the terminals one at a time using needle-nose pliers. Remove the old capacitor from its mounting strap. Install the new capacitor and reconnect terminals to their matching labels: HERM, FAN, COM.

Step 7 — Restore Power and Test

Close the access panel, restore power at the breaker, and test the system. Fan and compressor should start within seconds.

How to Choose the Right Replacement Capacitor

Match these three specs exactly from the original capacitor label:

MFD rating (both values — e.g. 45+5 MFD)
Voltage rating (370V or 440V — a 440V capacitor can replace a 370V, but not vice versa)
Physical shape (round vs oval) — affects mounting fit

How to Replace a Dual Run Capacitor: Step-by-Step Guide