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Capacitor Identification Chart

How to tell run, dual-run and start capacitors apart by case style and terminals, and how to read the label fields that must match on a replacement.

Ref HV-0046EIA-456-A

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

HVAC motors and compressors use two kinds of capacitors. Run capacitors are metallized film units that stay in the circuit while the motor runs. Start capacitors are electrolytic units that are only in the circuit for a moment at start-up. A dual run capacitor combines two run capacitors in one can, usually one for the compressor and one for the outdoor fan. EIA-456-A covers metallized film motor run capacitors.

How to identify

Case: Run capacitors usually have a metal can, round or oval. Start capacitors usually have a black plastic case, almost always round.
Terminals: A single run capacitor has two terminals, often with several tabs each. A dual run capacitor has three: C (common), HERM (compressor) and FAN.
Label: Read the full label before removing the old part. Take a photo.
Discharge first. Capacitors can hold a charge after power is off. Discharge safely with a proper tool before handling.

Label fields chart

Label field	What it means	Replacement rule
µF or MFD	Capacitance in microfarads	Match the rating. Dual units show two values, such as 45+5
Tolerance (for example ±5% or ±6%)	Allowed spread from the rated µF	Use for testing; replacement tolerance should be equal or tighter
VAC	Rated AC voltage, such as 370 or 440	Same or higher voltage rating
Hz	Rated frequency, usually 50/60	Match the supply
Temperature range	Allowed operating temperature	Same or wider range
Protected or P-marking	Has an internal pressure-sensitive interrupter	Use a protected unit where the original was protected
HERM / FAN / C	Terminal functions on dual units	Connect each wire to the same terminal
Start capacitor range (for example 88–108 µF)	Start caps are rated as a range	Match the range and voltage

Key points

Never swap a start capacitor for a run capacitor, or the reverse. Electrolytic start capacitors are not built for continuous duty.
A higher voltage rating is fine. A lower one is not.
A bulging top or leaking case means the capacitor has failed. Check the motor or compressor too.
Test with a meter that reads capacitance, with the capacitor out of the circuit and discharged.

Common mistakes

Swapping HERM and FAN wires on a dual capacitor.
Choosing a replacement by case size instead of µF and voltage.
Handling a capacitor without discharging it.

Governing standards: EIA-456-A (metallized film motor run capacitors); UL 810 (capacitors); the equipment wiring diagram and the motor or compressor manufacturer's data.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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