Dual Run Capacitor Symbol

The Dual Run Capacitor symbol (IEC 60617 / ANSI Y32.2).

Definition: The Dual Run Capacitor symbol represents two motor-run capacitors sharing one can and one common terminal — drawn as a round can outline with two capacitor plate pairs inside and three top terminals labelled C (Common), FAN, and HERM — used to phase-shift the start windings of an HVAC condenser's compressor and fan motors, per IEC 60252-1 (AC motor capacitors) and drawn with standard IEC 60617 / ANSI Y32.2 capacitor plate symbols.

Also known as: dual capacitor, run capacitor, dual round capacitor, HVAC capacitor, condenser capacitor, 45/5 capacitor, CBB65 capacitor, motor run capacitor.

What the Dual Run Capacitor symbol means

The Dual Run Capacitor symbol denotes a single metal can containing two independent run capacitors that share one common terminal. In a residential air-conditioner or heat-pump condensing unit it replaces two separate capacitors: the larger section (HERM, for 'hermetic compressor') serves the compressor motor and the smaller section (FAN) serves the condenser fan motor. Both sections connect on one side to the C (Common) terminal, which is fed from one leg of the 240 V contactor.

Electrically, each section is a run capacitor permanently in series with its motor's start (auxiliary) winding. It shifts the current in that winding roughly 90 electrical degrees out of phase with the main winding, creating the rotating magnetic field a permanent split capacitor (PSC) motor needs to develop torque and run efficiently. Unlike a start capacitor, a run capacitor stays in the circuit the entire time the motor operates, so it is built as a low-loss metallized polypropylene film capacitor in an oil-filled can rather than a short-duty electrolytic.

How to identify the Dual Run Capacitor symbol

In condenser-unit wiring diagrams the dual run capacitor is drawn as a round or oval can outline with three terminals across the top labelled C, FAN, and HERM, and two capacitor plate-pair symbols inside the outline — one for each section. The physical part matches the drawing: a round can with three multi-tab quick-connect terminal groups on top, each stamped with its letter.

Using pure schematic conventions, each section is just the standard capacitor symbol — two parallel plates (IEC 60617 and ANSI Y32.2 draw the non-polarized capacitor identically) — with one plate of each section tied to the common node. Some OEM diagrams draw the two sections as separate capacitors and note 'dual cap' beside them; the giveaway is the shared C node and the HERM/FAN labels, which are unique to HVAC practice rather than any IEC/ANSI lettering standard.

Function in a circuit

The dual run capacitor gives both PSC motors in a condensing unit their phase-shifted auxiliary current. Power flow: the contactor's load side feeds Common on the capacitor and the run windings of both motors; the HERM terminal connects to the compressor's Start (S) terminal, and the FAN terminal connects to the fan motor's start-winding lead (commonly the brown wire). When the contactor pulls in, current through each capacitor section leads the main-winding current, producing the rotating field that starts and runs each motor.

Because the capacitor is always energized while the unit runs, its microfarad value directly affects motor performance. A section that has drifted more than about 6–10% below its rating causes hard starting, low fan speed, compressor overheating, and high amp draw; a shorted section usually trips the breaker or stalls the motor. The bulged or domed top of a failed can is the classic visual symptom, caused by the internal pressure interrupter disconnecting the element.

Standards: IEC vs ANSI

IEC 60617	IEC 60252-1 is the governing standard for AC motor run capacitors, defining voltage classes, capacitance tolerance (commonly ±5%), temperature classes, and safety classes (P0/P1/P2 — P2 requiring a fail-safe disconnect mechanism). The schematic symbol is the standard IEC 60617 non-polarized capacitor (two parallel plates). CBB65 is the common Chinese-market designation for the round metal-can oil-filled type built to this standard.
ANSI/IEEE 315	In North America run capacitors are recognized under UL 810 (capacitors) and applied per the motor manufacturer's listing; EIA-456 historically covered motor capacitor practice. Diagrams use the ANSI Y32.2 / IEEE 315 capacitor symbol. The HERM/FAN/C terminal lettering is an HVAC industry convention rather than an ANSI standard, but it is universal on US equipment and replacement parts.
Key difference	There is no meaningful difference in the capacitor plate symbol between IEC and ANSI for non-polarized capacitors. The practical difference is in ratings culture: IEC 60252-1 parts are marked with safety class (P2) and duty class, while US parts emphasize the dual microfarad rating (e.g. 45/5 µF) and dual voltage rating (370/440 VAC). Terminal identification (C, FAN, HERM) is identical worldwide on HVAC dual caps.

Terminals / pins

Pin	Name
herm	HERM
fan	FAN
c	C (Common)

Typical values

Dual run capacitors are specified as two microfarad values — compressor section first — such as 35/5, 40/5, 45/5, 55/7.5, 60/5, up to about 80/10 µF. Voltage ratings are 370 VAC or 440 VAC (modern parts are usually dual-rated 370/440 V, and a 440 V part can always replace a 370 V part of the same µF). Capacitance tolerance is ±5–6%; replace when a section reads more than about 10% low. Operating temperature class is typically –40 °C to +70 °C, and design life ratings run from 10,000 to 60,000 hours per IEC 60252-1 duty classes.

Where the Dual Run Capacitor symbol is used

Residential central air-conditioner condensing units, serving the compressor (HERM) and condenser fan (FAN) motors
Heat-pump outdoor units, where the same dual capacitor runs the compressor and fan in both heating and cooling modes
Package/rooftop units (RTUs) on small commercial buildings using PSC condenser fans and hermetic compressors
Mini-split and window air conditioners (often with smaller dual or single run capacitors on the same C/FAN/HERM scheme)
Pool heat pumps and refrigeration condensing units using PSC fan motors and single-phase hermetic compressors
Replacement/service work — the dual run capacitor is among the most commonly replaced parts in HVAC service

Example

In a typical split-system condenser wiring diagram, the 240 V contactor load side feeds the compressor's R (Run) terminal, the fan motor's black lead, and the dual run capacitor's C terminal. The capacitor's HERM terminal wires to the compressor's S (Start) terminal, and the FAN terminal wires to the condenser fan motor's brown start-winding lead. A 45/5 µF, 440 VAC capacitor here means 45 µF between C and HERM for the compressor and 5 µF between C and FAN for the fan motor.

Key facts

A dual run capacitor is two run capacitors in one can with a shared Common terminal — HERM serves the compressor, FAN serves the condenser fan motor.
Common ratings are written compressor-first (e.g. 45/5 µF) with a 370 VAC or 440 VAC voltage class; a 440 V part can replace a 370 V part of equal microfarads, never the reverse.
Run capacitors stay in the circuit continuously while the motor runs, unlike start capacitors, so they are low-loss metallized polypropylene film types, not electrolytics.
The capacitor phase-shifts the start-winding current of a PSC (permanent split capacitor) motor by roughly 90°, creating the rotating field needed for starting torque and efficient running.
A section reading more than about 10% below its rated microfarads causes weak fan speed, hard compressor starts, and high amp draw; a bulged can top means the internal fail-safe has operated.
IEC 60252-1 governs motor run capacitors (tolerance ±5%, safety classes P0/P1/P2); UL 810 covers them in North America.
Always discharge a run capacitor across a resistor (or an insulated screwdriver blade in field practice) before handling — it can hold a charge at hundreds of volts after power-off.
Replacing a failed dual cap with two single capacitors (one for HERM, one for FAN, commons tied together) is electrically equivalent and a common field fix.

Frequently asked questions

What do C, FAN, and HERM mean on a dual run capacitor?

C is the Common terminal, fed from one leg of the contactor's load side and shared by both capacitor sections. HERM (for 'hermetic') is the compressor section terminal, wired to the compressor's Start terminal. FAN is the fan section terminal, wired to the condenser fan motor's start-winding lead (usually the brown wire). Each terminal is a group of multiple quick-connect tabs so several wires can land on it.

What does 45/5 µF mean on a capacitor?

It is the rating of the two sections: 45 µF between C and HERM for the compressor, and 5 µF between C and FAN for the fan motor. The compressor value is always listed first. A replacement must match both values (within tolerance) and have an equal or higher voltage rating — for example a 45/5 at 440 VAC can replace a 45/5 at 370 VAC.

What is the difference between a run capacitor and a start capacitor?

A run capacitor stays in the motor circuit continuously, so it is a low-loss oil-filled film capacitor with modest microfarads (typically 3–80 µF). A start capacitor is a high-value electrolytic (typically 88–400 µF) that is only in the circuit for a fraction of a second during starting and is disconnected by a potential relay or centrifugal switch. Leaving a start capacitor energized destroys it; the dual run capacitor on a condenser is purely a run capacitor.

How do I test a dual run capacitor?

Kill power at the disconnect, discharge the capacitor across a resistor, pull the wires (photograph them first), and measure each section with a multimeter's capacitance function: C-to-HERM should read the first number on the label, C-to-FAN the second. A reading more than about 10% below rating, an open section, or continuity between a terminal and the metal can means the capacitor should be replaced.

Can I replace a dual run capacitor with two single capacitors?

Yes — it is electrically identical. Use one capacitor matching the HERM value between the common feed and the compressor Start terminal, and another matching the FAN value between the common feed and the fan start lead, with both capacitors' common sides tied to the same contactor leg. Match microfarads and use equal-or-higher voltage ratings (370 or 440 VAC).

Why did my capacitor bulge on top?

Modern round-can capacitors have a pressure-sensitive interrupter: when the element overheats or fails internally, gas pressure pushes the can lid up, which physically tears the internal connections and safely disconnects the capacitor (IEC 60252-1 safety class P2 behavior). A domed or split top is definitive evidence of failure — replace the capacitor and check for causes such as overvoltage, excessive heat, or a failing motor.

Related symbols

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