Everything You Need Is Printed on the Can
The label on a run capacitor tells you exactly what to buy as a replacement — if you know how to read it. Most of the confusion around capacitors comes from three or four numbers that look technical but mean something simple. Here is what each one says.
The Capacitance: 45+5 µF
Capacitance is measured in microfarads, written µF or MFD (they mean the same thing). A label reading 45+5 µF describes a dual run capacitor — two capacitors sealed in one can:
- 45 µF — the larger section, which starts and runs the compressor
- 5 µF — the smaller section, which runs the condenser fan motor
Both numbers have to match your original. A 45+5 is not a substitute for a 40+5, even though the fan side is identical. CoralVolt dual run capacitors run from 5+5 µF up to 70+7.5 µF, which covers the large majority of residential and light commercial condensing units.
The Tolerance: ±5%
No capacitor is exactly its rated value. The tolerance tells you how far it is allowed to drift from the label and still be in spec. A 45 µF section rated ±5% may legitimately read anywhere between 42.75 and 47.25 µF on a meter. Below that range, the capacitor is weak and the compressor is working harder than it should. If you want to check yours, our guide to testing a capacitor with a multimeter walks through it.
The Voltage: 370/440 VAC
This is the maximum working voltage the capacitor is built for — not the voltage of your house. Older capacitors were rated 370 V; most modern ones are dual-rated 370/440 VAC, which means one part replaces either. The rule is simple: voltage can go up, never down. A 440 V capacitor is a correct replacement for a 370 V original. A 370 V part fitted where 440 V was specified will run hot and fail early.
CBB65 and the Other Small Print
- CBB65 — the construction type: a metallised polypropylene film capacitor in a sealed metal case, the standard for HVAC run duty
- 50/60 Hz — the line frequencies it is rated for; US mains is 60 Hz
- -40°C to +70°C — operating temperature range, which is why a capacitor tucked beside a hot compressor in July is the one most likely to fail
- 10,000 AFC — the available fault current the safety design is tested against
- UL or UR mark — the component has been evaluated by Underwriters Laboratories
The Terminals: HERM, FAN and C
On top of a dual run capacitor you will find three clusters of spade terminals, each marked:
- C — common. Connects to the contactor and is shared by both sections.
- HERM — hermetic, meaning the compressor. This is the larger µF section.
- FAN — the condenser fan motor. This is the smaller section.
When you replace a capacitor, each wire goes back to the terminal with the same marking. Photograph the old one before disconnecting anything.
Round or Oval
The shape is a mounting decision, not an electrical one. Round and oval capacitors with the same ratings are interchangeable; pick the one that fits the strap already in your unit.
Safety
A capacitor holds a charge after the power is off. Before touching the terminals, isolate the unit at the breaker and the outdoor disconnect, and discharge the capacitor properly — see our guide on safely discharging an AC capacitor. If you are not confident doing that, this is a job for a licensed HVAC technician.
Buying more than one? The same sizes are available in multi-packs of 4, 6 and 10 at a lower unit price.