Capacitor Wiring Diagram: Motor Connection Guide

Walk up to any single-phase motor — whether it’s an HVAC compressor, a condenser fan, a well pump, or an industrial blower — and behind the access panel you’ll almost always find one or two capacitors doing critical work. Understanding the capacitor wiring diagram for that motor is the difference between a clean repair job and a burned winding or a blown replacement part. This guide covers every common motor capacitor configuration, the terminal labeling system that trips up most first-timers, step-by-step wiring instructions, and the troubleshooting knowledge that comes from actually working on these circuits.

Why Single-Phase Motors Need Capacitors

Three-phase motors start themselves because the three staggered AC phases naturally create a rotating magnetic field in the stator. Single-phase motors don’t have that luxury — they receive only one alternating current, which creates a pulsating rather than rotating field. On its own, a single-phase motor cannot start; it needs a phase-shifted auxiliary winding current to generate the initial torque that gets the rotor moving.

Capacitors create that phase shift. By introducing a capacitor in series with the auxiliary (start) winding, the current in that winding leads or lags the main winding current by up to 90 degrees, producing enough of a rotating field to generate starting torque. Once running, either the start capacitor is switched out of the circuit by a centrifugal switch, or a run capacitor remains connected permanently to improve efficiency and power factor. The specific capacitor wiring diagram you need depends entirely on which of these configurations your motor uses.

For a solid overview of capacitor types — including the differences between electrolytic start capacitors and film-type run capacitors — PCBSync’s capacitor reference explains the construction differences that make each type suited to its specific role.

The Three Motor Capacitor Configurations

Before touching a single wire, you need to identify which configuration your motor uses. Getting this wrong is how windings burn.

Capacitor Start (CS) Motor

The capacitor start motor uses a large electrolytic capacitor in series with the start winding and a centrifugal switch. When power is applied, current flows through both the main winding and the start winding (via the capacitor), creating the phase shift needed for starting torque. Once the motor reaches approximately 75% of its rated speed, the centrifugal switch opens and disconnects the start capacitor entirely. The motor then runs on its main winding only.

Identifying features: One capacitor, typically cylindrical and rated 70–400µF at 125V or 250V AC. A centrifugal switch inside the motor housing.

Starting torque: High — typically 150–350% of full load torque.

Common applications: Compressors, pumps, large fans, machine tools.

Permanent Split Capacitor (PSC) Motor

The PSC motor uses a single run capacitor that stays permanently in circuit — there is no centrifugal switch. The capacitor lives in series with the auxiliary winding at all times, improving both starting and running characteristics, though starting torque is modest compared to a CS motor.

Identifying features: One capacitor, typically rated 2–70µF at 370V or 440V AC. Motor body will not have a centrifugal switch. Common in HVAC condenser fan motors.

Starting torque: Low to medium — 30–150% of full load torque.

Common applications: HVAC fan motors, small pumps, ceiling fans, refrigerators.

Capacitor Start Capacitor Run (CSCR) Motor

The CSCR motor uses both a start capacitor and a run capacitor. The large start capacitor provides high starting torque; once the motor is up to speed, the centrifugal switch disconnects the start capacitor and the smaller run capacitor remains in circuit permanently for efficient operation.

Identifying features: Two capacitors — a large electrolytic start cap and a smaller film-type run cap. Centrifugal switch present inside the motor.

Starting torque: Very high — up to 350–400% of full load torque.

Common applications: Air compressors, heavy-duty pumps, woodworking equipment, industrial blowers.

Motor Type Comparison

Motor Type	Capacitor(s)	Centrifugal Switch	Starting Torque	Common Use
Capacitor Start (CS)	1 start cap	Yes	High (150–350%)	Compressors, pumps
Permanent Split Capacitor (PSC)	1 run cap	No	Low–Medium (30–150%)	HVAC fans, small appliances
Capacitor Start Capacitor Run (CSCR)	1 start + 1 run cap	Yes	Very High (350–400%)	Industrial equipment
Split Phase (no capacitor)	None	Yes	Medium	Light-duty fans, tools

Understanding Motor Terminal Labels

This is where most wiring mistakes originate. The terminal labels on the motor and the terminals on the capacitor follow different naming conventions, and they need to be matched correctly.

Motor Winding Terminals

Motor Terminal Label	Meaning	Notes
M or MAIN	Main winding	Carries current during running
S or START or AUX	Start / auxiliary winding	Carries current only during starting (CS) or always (PSC/CSCR)
C or COMMON	Common connection for both windings	Connected to one side of the power supply
R	Run winding	Alternate label for main winding on some motors

Capacitor Terminal Labels (HVAC Dual Run Capacitor)

Capacitor Terminal	Meaning	What Connects Here
C or COM	Common	Line voltage from contactor; bridges the two motor circuits
HERM or H	Hermetic compressor	Start winding lead from the compressor motor
FAN or F	Fan	Start winding lead from the condenser fan motor

The critical thing to understand about HVAC dual run capacitors is that one capacitor serves two separate motors simultaneously — the compressor and the condenser fan. The C (common) terminal is the shared connection point. When you disconnect all three wires and don’t label them first, you’re looking at a puzzle with no solution other than the wiring diagram inside the unit’s access panel.

Capacitor Wiring Diagram: Single Run Capacitor (PSC Motor)

This is the simplest configuration and the most common in HVAC condenser fan motors and small appliance motors.

Connections:

• One terminal of the capacitor connects to the start/auxiliary winding lead of the motor
• The other terminal of the capacitor connects to the common winding lead (and to one side of the supply line)
• The main winding connects directly to the supply line (both terminals, bypassing the capacitor)

In practice, the capacitor sits across the auxiliary winding, with both the motor’s common terminal and the supply line sharing the capacitor’s second terminal through the motor’s internal wiring. This is why, when you look at a PSC motor’s lead configuration, you typically see three external wires: two for the main winding (going directly to line voltage) and one from the auxiliary winding that connects to the capacitor, with the other side of the capacitor returning to the common line.

Wire color conventions for HVAC condenser fan motors (verify against your specific unit’s diagram):

Wire Color	Connection
Black	High voltage supply (contactor to motor)
White	Common (often connects to C terminal on dual cap)
Brown	Fan terminal on run capacitor
Brown/White	Unused in 3-wire connection; cap off safely
Purple	Compressor start winding (to HERM terminal)
Orange or Red	Common from contactor to C terminal

Note: wire colors are conventions, not standards. The equipment’s own wiring diagram, usually found inside the unit’s access panel, is the authoritative source. Never assume based on color alone.

Capacitor Wiring Diagram: Dual Run Capacitor (HVAC Compressor + Fan)

The dual run capacitor is the configuration that generates the most confusion in the field. Here’s how the connections work, systematically:

Step 1: Identify the three terminals on the capacitor — C (common), HERM (compressor), FAN.

Step 2: Connect the wire coming from the contactor (line voltage) to the C terminal. This feeds both motor circuits through the common.

Step 3: Connect the compressor’s start winding wire (often purple or the wire labeled HERM on the compressor) to the HERM terminal.

Step 4: Connect the fan motor’s auxiliary winding wire (often brown) to the FAN terminal.

The fan motor’s main winding connects directly back to the contactor for line voltage — it does not go through the capacitor. The capacitor is only in the auxiliary winding path.

Dual Run Capacitor Terminal Connection Summary

Capacitor Terminal	Wire Source	Notes
C (Common)	Contactor output (L2 or line voltage)	Shared power input for both motor circuits
HERM	Compressor start winding	Typically purple wire from compressor
FAN	Fan motor auxiliary winding	Typically brown wire from fan motor

Capacitor Wiring Diagram: Capacitor Start Capacitor Run (CSCR) Motor

In a CSCR motor, the start capacitor and run capacitor are both in the start winding circuit during startup, but the start capacitor gets switched out once running speed is reached.

Connections:

• Run capacitor: Connected permanently in series with the auxiliary winding, between the auxiliary winding terminal and the common terminal. Both motor terminals and the capacitor form a closed loop here.
• Start capacitor: Connected in parallel with the run capacitor (across its terminals), but in series with the centrifugal switch. When the switch opens at running speed, the start capacitor is disconnected, leaving only the run capacitor in circuit.

In practice, the start capacitor and its centrifugal switch are sometimes located inside the motor housing, with only the run capacitor as an external component. In external configurations, three terminals are typically accessible: the main winding, the auxiliary winding, and the common. The run cap connects between auxiliary and common; the start cap (in series with a relay or switch) connects across the run cap.

Step-by-Step: Replacing a Motor Capacitor Safely

Whether you’re replacing a failed run capacitor on an HVAC unit or swapping a blown start cap on an industrial compressor, the process follows the same safety-critical sequence.

Before you touch anything:

Turn off power at the breaker, not just at the unit switch. Use a multimeter to verify that voltage is absent at the motor terminals. Even after power is removed, capacitors can hold a dangerous charge — a 370V run capacitor or a 250V start capacitor can deliver a shock capable of causing serious injury. Discharge the capacitor before handling: use an insulated screwdriver to short each terminal to the capacitor’s case, or on a dual cap, short from C to HERM and from C to FAN.

Replacement process:

Step	Action	Notes
1	Photograph all wiring connections	Critical — before removing a single wire
2	Label each wire with tape	Especially if wires are the same color
3	Disconnect wires one at a time	Record which terminal each came from
4	Remove the failed capacitor	Note its µF and voltage rating
5	Match replacement rating exactly	Never substitute a lower µF or voltage value
6	Reconnect wires per your photograph/notes	Match terminal labels exactly
7	Verify all connections are secure	Loose spade connectors cause arcing
8	Restore power and test	Check for proper startup and running operation

On matching replacement specifications: A run capacitor rated 35µF/5µF at 440VAC for an HVAC unit cannot be substituted with a 35µF/5µF at 370VAC part if the supply voltage reaches 380–400V. 440VAC-rated parts are always acceptable substitutes for 370VAC-rated ones; the reverse is not safe. On µF values: an incorrect run capacitor value causes the motor to draw incorrect current, run hot, and fail prematurely. A ±5% tolerance on µF rating is generally acceptable; more than that requires a correctly rated replacement.

Troubleshooting Motor Capacitor Problems

Capacitor failure is one of the most common reasons a motor fails to start or runs poorly. Knowing what to look for saves diagnostic time.

Symptom	Likely Cause	Diagnostic Step
Motor hums but won’t start	Failed start capacitor or centrifugal switch stuck closed	Test capacitor with capacitance meter; check switch operation
Motor starts but runs hot and slow	Failed or wrong-value run capacitor	Measure run capacitor µF; compare to nameplate value
Motor trips overload on startup	Start capacitor shorted, or too-low µF value	Test capacitor; check for shorts to case
Capacitor body bulging or leaking	Internal failure — electrolyte degradation	Replace immediately
Burning smell from motor area	Overloaded winding due to absent capacitor	Inspect both capacitor and winding resistance
AC not cooling — compressor won’t run	Dual capacitor failure on HERM side	Test both sections of dual cap
Fan doesn’t run — compressor runs normally	Dual capacitor failure on FAN side	Test FAN section of dual cap specifically

Testing a capacitor with a multimeter (capacitance setting): Measure the actual µF value against the nameplate. A run capacitor measuring more than 10% below its rated value is degraded; replace it. A reading of near-zero or OL on the capacitance setting indicates an open or shorted capacitor. An ESR meter adds further diagnostic resolution but is less commonly available in field kits.

Useful Resources for Motor Capacitor Wiring

Resource	What You’ll Find	Link
InspectAPedia Motor Capacitor Guide	Comprehensive HVAC and motor capacitor wiring instructions and color code tables	inspectapedia.com
Dreisilker Electric Motors	Condenser fan motor 3-wire and 4-wire wiring guide with diagrams	dreisilker.com
Electricalsphere CSCR Motor Guide	Technical wiring diagram and theory for CSCR induction motors	electricalsphere.com
HVAC How-To — Start and Run Capacitors	Field-focused guide covering capacitor types, ratings, and wiring	hvachowto.com
Mouser Electronics	Capacitor inventory with parametric search by µF, voltage, and type	mouser.com
DigiKey	Full capacitor database for sourcing replacement run and start capacitors	digikey.com
PCBSync Capacitor Guide	Capacitor types, construction, and selection fundamentals	pcbsync.com/capacitor

5 Frequently Asked Questions About Capacitor Wiring Diagrams

Q1: How do I know which wire goes to which terminal on my dual run capacitor if nothing is labeled?

Start with the wiring diagram on the inside of the unit’s access panel — it will show the capacitor schematically with terminal labels and wire colors for that specific model. If the diagram is missing or unreadable, use a multimeter in continuity or resistance mode to identify the motor windings. On the compressor, measure resistance between the three terminals (if accessible): the lowest resistance reading identifies the run winding (R to C), the slightly higher reading identifies the start winding (S to C), and the highest reading is the sum of both (R to S). The start winding terminal goes to HERM on the dual cap. On the fan motor, the auxiliary winding lead goes to FAN, and the common goes to C. When in doubt, trace each wire from its motor connection point back to the capacitor rather than assuming based on color.

Q2: Can I replace a dual run capacitor with two separate single run capacitors?

Yes, and in a pinch this is a legitimate field repair. The compressor’s run capacitor value (in µF) equals the HERM rating of the dual cap, and the fan’s run capacitor equals the FAN rating. Connect each single cap’s terminals between the relevant motor’s start winding and the common supply line, the same way the dual cap’s HERM-to-C and FAN-to-C sections were wired. Voltage ratings must meet or exceed the original dual cap specification (typically 370V or 440VAC). Keep both capacitors in the same general location and ensure they’re secured against vibration.

Q3: What happens if I wire the start capacitor where the run capacitor should be?

The motor will likely fail quickly. Start capacitors are electrolytic types rated for intermittent duty — typically 1–3 seconds of energization at a time. Leaving a start capacitor permanently in circuit (where a run capacitor should be) causes it to overheat and fail within minutes. The reverse — placing a film-type run capacitor in the start position — usually means the motor won’t start at all, or starts very weakly, because run capacitors have much lower µF values than start capacitors. Always use the correct type in each position.

Q4: My replacement capacitor has the same µF rating but a different voltage rating. Is it safe?

If the voltage rating of the replacement is equal to or higher than the original, it’s safe to use. A 370VAC capacitor replacing a 370VAC original is fine; a 440VAC replacing a 370VAC original is also acceptable — the higher voltage rating simply means the component is built to a more robust specification and will operate safely at the same supply voltage. Never install a capacitor with a lower voltage rating than the original. The risk isn’t just gradual degradation; a capacitor operating above its rated voltage can fail catastrophically.

Q5: After replacing the capacitor, the motor starts but the fan runs in reverse. What happened?

Reversed fan rotation after a capacitor replacement typically means the run capacitor is connected to the wrong winding terminal. On a PSC motor, swapping which winding the capacitor leads are connected to reverses the phase shift direction and therefore reverses the direction of rotation. Check the motor’s wiring diagram for the correct terminal assignment and swap the auxiliary winding lead if the direction is inverted. Some motors have a labeling convention where swapping the run cap connection is actually the documented method for changing rotation direction — worth checking the motor nameplate or spec sheet before assuming something is wired incorrectly.

Wrapping Up

The capacitor wiring diagram for any motor is really a story about phase relationships: which winding gets phase-shifted by the capacitor, for how long, and how the circuit changes between starting and running conditions. Once you understand that underlying logic — and know how to read the terminal labels on both the motor and the capacitor — the physical wiring becomes straightforward. The most important habits are photographing before disconnecting, matching replacement capacitor ratings exactly (both µF and voltage), and always discharging capacitors before handling. Get those right and motor capacitor work is one of the more approachable repairs in the electrical service toolkit.