AC Capacitor Wiring Colors: Complete Color Code Guide for Dual Run Capacitors (C, FAN, HERM)

AC capacitor wiring uses a standard color-coding system to connect three main terminals on a dual run capacitor: brown for the FAN terminal, yellow for the HERM (compressor) terminal, and red, orange, or black for the C (Common) terminal. Understanding these wire colors is essential for any AC capacitor installation, maintenance, or replacement, as correct wiring ensures the safe and efficient operation of the compressor and fan motors in an HVAC system.

This guide covers the standard AC capacitor wire color code, the types of capacitors used in AC systems, how to identify and connect each wire, how to read a dual run capacitor wiring diagram, common wiring issues, safety precautions, testing procedures, and best practices for proper installation.

Quick reference — AC capacitor wire colors:

Brown → FAN terminal (fan motor)
Yellow → HERM terminal (compressor)
Red / Orange / Black → C (Common) terminal (power source)
Green / Green-Yellow → chassis ground (never connects to capacitor terminals)

Introduction to AC Capacitor Wiring Colors

AC capacitors are essential components in air conditioning systems, serving as energy storage units that power the compressor and fan motor — the key components for system operation. These devices store electrical energy and release it on demand to start and run these motors efficiently. A malfunctioning capacitor or incorrectly wired connection can significantly degrade the overall performance of an air conditioning system.

Proper wiring of AC capacitors is critical, as it ensures the safe and effective transfer of electrical energy to the system’s operational components. The wires are color-coded not merely for identification but to indicate specific functional connections. Understanding this color coding is important for anyone performing installation, maintenance, or repair on an AC unit. Correct application of the color code ensures that each connection is made properly, aligning all components for optimal function and reducing the risk of electrical faults or equipment damage.

Types of AC Capacitors

AC capacitors used in air conditioning systems are categorized into three main types, each with its own wiring configuration:

Start Capacitor

A start capacitor provides a high-energy pulse needed to overcome the motor’s initial static resistance when the system first powers on. This burst of energy helps the motor begin rotating, and once the motor reaches operational speed, the start capacitor is disconnected from the circuit by a potential relay. Start capacitors typically have a higher capacitance value (usually 70 µF and above) and are designed for short-duration use only.

Run Capacitor

A run capacitor remains active throughout the motor’s operational cycle, providing a steady electrical current that helps maintain motor speed and stability. Run capacitors have a lower capacitance value than start capacitors (usually 3-60 µF) and are built for continuous operation. They are commonly used in both the compressor and fan motor circuits.

Dual Run Capacitor

A dual run capacitor combines the functions of two run capacitors into a single unit, supporting both the compressor and the fan motor. This is the most common type of capacitor found in modern residential AC systems. A dual run capacitor has three terminals (C, FAN, HERM) and is labeled with two capacitance values, such as 45/5 µF, where the larger value serves the compressor and the smaller value serves the fan motor.

Each capacitor type has specific wiring requirements based on its role in the system. Understanding which type is installed is the first step in correctly interpreting the wire colors connecting to it.

Common AC Capacitor Wire Colors and Their Meanings

Each wire color connecting to an AC capacitor corresponds to a specific terminal and function within the HVAC system:

Brown Wire

The brown wire connects the capacitor to the fan motor. It supplies the phase-shifted current needed to start and run the condenser fan motor. A correct brown wire connection to the FAN terminal is essential for proper air circulation through the outdoor unit. A loose or incorrect brown wire connection can prevent the fan from starting or cause it to run inefficiently.

Yellow Wire

The yellow wire connects the capacitor to the compressor. It supplies power to the compressor’s start winding, which is necessary for the refrigeration cycle that produces cooling. A correct yellow wire connection to the HERM terminal ensures the compressor starts reliably and runs at the correct speed. An incorrect connection can prevent the compressor from starting or cause it to draw excessive current, potentially leading to overheating or motor failure.

Common Wire (C)

The common wire connects the capacitor to the power source through the contactor. This wire is often colored red, orange, or black, depending on the manufacturer. The common wire completes the electrical circuit between the capacitor and the contactor’s T2 terminal, providing the line voltage feed that powers both capacitor sections. Correct identification and connection of the common wire is essential for the entire capacitor circuit to function.

Accurate identification of these three wires and their corresponding terminals is the foundation of AC capacitor wiring. Always verify each connection against the wiring diagram printed on the unit’s access panel before powering the system.

AC Capacitor Wiring Color Code

The standard AC capacitor wiring color code identifies each wire by its function and destination terminal. The following summary table covers the most common wire colors found on North American AC capacitors:

Wire Color	Terminal	Connected Component	Notes
Red (R)	C (Common)	Power source / Contactor T2	Common connection for both fan and compressor circuits
Brown (BR)	FAN	Condenser fan motor	Standard wire for the condenser fan start winding
Brown with White stripe	FAN	Fan motor (secondary lead)	Often paired with solid brown on some units
Yellow (Y)	HERM	Compressor	Powers the hermetically sealed compressor start winding
Blue (BL)	C or HERM	Common or Compressor	Alternate color on certain systems
White (W)	C or Neutral	Common / Power supply	Sometimes used as neutral or alternate common
Orange (O)	FAN or HERM	Fan or Compressor	Common in Goodman/Amana units
Black (BK)	L1 / C	Main power line or Common	Often comes from the contactor
Purple (P)	FAN or HERM	Fan or Compressor	Less common; consult wiring diagram
Green (G)	Ground	Chassis / Earth ground	Never connects to any capacitor terminal

Following this color code during installation or replacement is essential. Miswiring can lead to system malfunctions including motor failure, reduced efficiency, increased wear on components, or electrical hazards. Each wire must be connected to its designated terminal according to the wiring diagram.

Additional Wiring Colors

In addition to the standard color code, AC systems may include additional wire colors depending on the manufacturer and system design:

Black: Commonly used as the common wire on many capacitor installations, completing the electrical circuit to the power source.
Red: Often used as an alternative color for the common wire, or in some systems as a start winding connection.
Orange: Sometimes used for the common wire connection, particularly in certain brand configurations.
Purple: Occasionally used for the compressor’s start winding, providing the initial energy required to start the compressor.
White: Sometimes connected to the compressor’s common terminal in certain system configurations.
Blue: May be used for the common wire on imported systems or specific manufacturer configurations.

Understanding these variations is helpful when working with units from different manufacturers. Always consult the manufacturer’s wiring diagram when colors deviate from the standard to ensure each wire is connected to the correct terminal.

Standard and Non-Standard Color Codes

Most AC capacitor installations follow the standard color code described above, but variations can arise from differing manufacturing processes, regional electrical standards, or previous repair work. When encountering non-standard wire colors:

Consult the manufacturer’s wiring diagram, typically printed on the inside of the unit’s access panel or available in the service manual.
Reference authoritative guidelines such as the National Electric Code (NEC) for North American installations.
Verify each wire’s endpoint by tracing it to the motor or component it connects to, rather than relying solely on color.

This ensures the AC unit is wired correctly and reduces the risk of misconnections that could lead to equipment failure or safety hazards. When a previous technician has replaced wires with non-standard colors, tracing each wire back to its source is the only reliable identification method.

AC Dual Capacitor Wiring Diagram

Dual capacitors integrate the functions of two run capacitors into a single unit with three terminals. Understanding the wiring setup for a dual run capacitor is essential for correct installation and replacement:

C (Common): Connects to the power source through the contactor’s T2 terminal. The wire is typically red, orange, or black. This terminal serves as the shared electrical junction for both the fan and compressor capacitor sections.
FAN: Connects to the fan motor’s start winding. The wire is typically brown.
HERM: Connects to the compressor’s start winding. The wire is typically yellow.

{{INSERT_DIAGRAM: dual run capacitor wiring diagram showing C, FAN, HERM terminals with wire colors and connections to contactor, compressor, and fan motor}}

The wiring diagram typically shows the following connections:

[Power Source] → [Contactor L1/L2]
    ├── L1 → Compressor RUN winding → Fan Motor RUN winding
    └── L2 (T2) → C terminal on Dual Capacitor
                    ├── FAN section → Fan Motor START winding (brown wire)
                    └── HERM section → Compressor START winding (yellow wire)

[Chassis Ground] → Unit frame (never to capacitor terminals)

Each wire must be connected to its correct terminal to avoid operational failures. Before powering the unit, verify each connection by comparing it to the wiring diagram and performing continuity checks with a multimeter.

How to Read an HVAC Wiring Diagram

An HVAC wiring diagram uses standardized symbols to represent each component in the AC unit. Understanding these symbols helps trace each wire from the capacitor to the correct motor or control:

Capacitor: Shown as two parallel lines (sometimes one curved) labeled with its microfarad value. A dual run capacitor shows three terminals labeled C, FAN (or F), and HERM (or H).
Motor: Drawn as a circle with an “M” inside, often labeled “Comp” for the compressor or “Cond Fan” / “CFM” for the condenser fan motor.
Contactor: Shown as a rectangle with internal switches, labeled L1, L2 on the line side and T1, T2 on the load side.
Wires: Represented by lines. Colors are typically abbreviated: BRN for Brown, YEL for Yellow, RED for Red, ORN for Orange, PPL for Purple, BLK for Black, BLU for Blue, GRN for Green.
Terminals: Small dots or labeled connection points on each component.

To interpret the diagram, trace each wire to and from the capacitor:

The wire to the FAN terminal should connect to the condenser fan motor, typically labeled BRN.
The wire to the HERM terminal should connect to the compressor motor, typically labeled YEL.
The wire to the C terminal should connect to the contactor’s T2 terminal, typically labeled RED, ORN, or PPL.
Line voltage (L1, L2) enters the contactor and feeds the motor run windings and the capacitor C terminal.

Before working with any wiring, confirm that the diagram matches the specific model number of the unit. Older or revised models may use slightly different layouts.

AC Capacitor Terminal Labels vs. Wire Colors

The labels on the capacitor itself (C, FAN, HERM) are the definitive reference for where each wire connects. Wire colors serve as a visual guide that helps speed up identification, but terminal labels take priority in every case.

Matching Wires to Capacitor Terminals

C (Common): Connect the wire that provides power from the contactor’s T2 terminal. This wire is usually red, orange, or purple, though it can be other colors. The terminal label must be C.
FAN: Connect the wire that runs to the condenser fan motor. This wire is usually brown. The terminal label must be FAN (or F).
HERM: Connect the wire that runs to the compressor. This wire is usually yellow. The terminal label must be HERM (or H).

When Wire Colors Don’t Match the Standard

Wire colors serve as a strong indicator for quick identification — approximately 95% of the time, brown connects to FAN, yellow to HERM, and red/orange/purple to C (Common). However, several situations may cause colors to deviate:

A wire has faded due to sun exposure and is no longer clearly identifiable.
The unit is older or uses a less common brand with different color conventions.
A wire was replaced during previous service with a non-standard color.
The C (Common) wire in particular has the most color variance across manufacturers.

In any of these cases, rely on the terminal labels as the final authority, verify the wire’s destination using the wiring diagram, and use a multimeter to trace wires when needed.

Tips for Identifying Faded or Miscolored Wires

When wire colors are unclear, the following methods help confirm each wire’s function:

Continuity test with a multimeter: Check where a wire runs by testing continuity between its two ends.
Voltage test: With the system powered (and handled safely), measure voltage between wires to confirm which is hot (L1/L2), which is common (C), and which connects to the fan or compressor.
Check the manufacturer’s manual: The wiring diagram on the access panel or in the service manual identifies each wire by color and terminal.
Trace to the motor: Physically follow each wire from the capacitor to its endpoint. The wire ending at the compressor’s S (start) terminal is HERM; the wire ending at the fan motor’s start winding is FAN.

When multiple wires are burnt, melted, or unreadable, or when the capacitor values are missing, consulting a licensed HVAC technician is the safest approach.

Common Issues with AC Capacitor Wiring

AC capacitor wiring is prone to several issues that can affect system performance and safety. The following are the most common problems encountered during installation or troubleshooting:

Improper Wiring

Incorrect or loose wiring connections are the most common cause of capacitor-related failures. Symptoms of improper wiring include the system failing to start, the compressor humming without running, the fan running but the compressor not engaging, or the breaker tripping when the system attempts to start. Improper wiring is typically diagnosed by carefully inspecting each wire connection against the capacitor terminals and the wiring diagram, verifying that brown connects to FAN, yellow connects to HERM, and the common wire connects to C.

Loose Spade Connections

Wires that are not firmly seated on the capacitor’s spade terminals can arc under load, generating heat that damages the terminal plastic, the wire insulation, and eventually the capacitor itself. Loose connections often cause intermittent operation — the system may start normally one day and fail the next. Always push each wire connector firmly onto the terminal until it clicks or seats snugly, and perform a gentle tug test to confirm a secure connection.

Wiring Damage from Overheating

Capacitor terminals and nearby wiring can overheat when connections are loose, wire gauge is undersized, or the capacitor itself is failing. Signs of overheating at the wiring level include discolored insulation, melted spade connectors, or a distorted terminal on the capacitor. Overheated wires should be replaced with the same color and gauge, and the root cause (loose connection, wrong capacitor rating, or failing capacitor) should be identified before returning the system to service.

Miswiring After Replacement

When a capacitor is replaced, it is common for wires to be reconnected to the wrong terminals — especially when the original wire colors have faded or a previous technician used non-standard colors. This is why labeling each wire during disconnection and verifying connections against the wiring diagram before powering up is essential. Prompt identification of miswiring prevents motor damage and system failure.

Regular inspection of the capacitor wiring during routine HVAC maintenance helps detect these issues early, before they lead to more severe system problems.

Safety Precautions When Dealing with AC Capacitors

Handling AC capacitors safely is essential to prevent injuries and equipment damage. The following safety protocols must be rigorously followed:

Disconnect all power to the air conditioning system before beginning any work. Turn off the breaker at the main panel and pull the outdoor disconnect. This is the most important step in preventing electrical shock.
Verify power is off using a multimeter to check voltage at the contactor’s line terminals before touching any component.
Discharge the capacitor using a 10,000-20,000 ohm resistor rated at 2 watts or higher, or an insulated screwdriver with a thick plastic handle. Capacitors can retain lethal charge even after the power is disconnected.
Wear personal protective equipment including insulated gloves and safety goggles to protect against accidental shock and physical injury.
Never touch capacitor terminals with bare hands, even after discharging. Use tools with insulated handles for all connections.

Adhering to these safety measures reduces the risk of accidents during capacitor maintenance or replacement and ensures the integrity of the AC system.

{{INSERT_PHOTO: real dual run capacitor installed in AC condenser unit with wires visible}}

How to Test AC Capacitor Wiring and Connections

Testing AC capacitor wiring verifies that each wire is connected to the correct terminal and that the capacitor itself is functioning within specification. The process combines visual inspection, continuity testing, and capacitance measurement.

Power Off the AC System

Turn off the breaker at the main panel and pull the outdoor disconnect. Verify power is completely off using a multimeter before proceeding. This is the primary safety step that must be completed before any testing.

Discharge the Capacitor

Use a resistor or insulated screwdriver to safely discharge any residual charge stored in the capacitor. Confirm the capacitor reads under 2V DC across each terminal pair before touching.

Verify Wire Connections Against the Diagram

Before measuring any values, visually inspect each wire connection:

The brown wire should be connected to the FAN terminal and trace physically to the condenser fan motor.
The yellow wire should be connected to the HERM terminal and trace physically to the compressor.
The common wire (red, orange, or black) should be connected to the C terminal and trace back to the contactor’s T2 terminal.

Compare each connection to the wiring diagram on the access panel. If any wire is on the wrong terminal, correct it before powering the system.

Measure Capacitance with a Multimeter

Use a multimeter that includes a capacitance measurement mode. Set the multimeter to the correct capacitance range and connect the test leads to the capacitor terminals:

For a dual run capacitor: measure between C and FAN, then between C and HERM. The readings should match the two values printed on the capacitor label (e.g., 5 µF for the fan section, 45 µF for the compressor section).
For a single run capacitor: measure across the two terminals and compare to the rated value.

Compare Capacitance Value

Compare the multimeter reading to the specifications printed on the capacitor. A run capacitor should read within ±6% of its rated value. A reading outside this tolerance indicates the capacitor is failing and should be replaced, and the wires reconnected to the new capacitor following the correct color code.

Regular testing of both wiring connections and capacitance values allows early detection of problems before they cause system failure.

Proper AC Capacitor Wiring Procedure

Replacing and rewiring an AC capacitor follows a systematic sequence to ensure safety and correct connection. The procedure below applies to most residential dual run capacitor replacements:

Ensure power is off at the main breaker. Locate the breaker for the outdoor AC unit at the main electrical panel and flip it to the OFF position.
Disable the outdoor disconnect. At the disconnect box next to the condenser unit, pull out the disconnect block or flip the switch to OFF. Both power sources must be disabled before proceeding.
Access the capacitor. Unscrew the access panel on the condenser unit. Set the screws aside in a safe location.
Locate and document the capacitor. Find the capacitor — a round or oval metal cylinder with wires attached to terminals on top. Take multiple clear photos of the existing wiring from different angles before disconnecting anything.
Discharge the capacitor. Using an insulated screwdriver (plastic handle only) or a 10,000-20,000 ohm resistor rated 2W or higher, short across C and FAN terminals, then across C and HERM terminals. Repeat several times per terminal pair to ensure full discharge.
Disconnect wires one at a time. Pull each spade connector off the capacitor terminal individually. Immediately label each wire with masking tape or a marker indicating its original terminal (C, FAN, or HERM).
Remove the old capacitor. After all wires are disconnected and labeled, unscrew the mounting clamp or strap and remove the old capacitor.
Verify specifications of the replacement capacitor. Match the microfarad rating exactly (e.g., 45/5 µF must be replaced with 45/5 µF). Voltage rating must be equal or higher (440V can replace 370V, but not the reverse).
Install the new capacitor. Mount the new capacitor in the original location using the same clamp or strap, oriented so the terminal labels are clearly visible.
Reconnect each wire by label. Attach each wire to the terminal that matches its label — the wire labeled “HERM” connects to HERM, “FAN” to FAN, “C” to C. Push each connector firmly onto its terminal until it clicks or seats snugly.
Verify all connections. Visually inspect each connection against the photos taken earlier and the wiring diagram on the access panel. Perform a gentle tug test to confirm each connector is secure.
Restore power and test. Replace the access panel. Push the disconnect back in, then turn the main breaker back on. Set the thermostat to cool and verify the system starts cleanly — the fan spins up smoothly, the compressor hums steadily, and no unusual noises or breaker trips occur.

HVAC Capacitor Wiring: Tips and Tricks

Effective HVAC capacitor wiring ensures optimal performance and safety. Key practices include:

Follow the manufacturer’s wiring specifications, which are designed for the specific model and account for its unique operational requirements.
Test the capacitor with a multimeter both before and after making connections. This confirms the capacitor is functional and that the installation has not introduced any faults.
Label wires before disconnecting them during maintenance or replacement. This prevents confusion during reconnection and ensures each wire returns to its correct terminal.
Use the correct wire gauge for each connection. Undersized wire can overheat under load and cause voltage drops or insulation damage.
Take clear photos of the existing wiring before disconnecting anything. Photos provide a reliable reference for reconnection when a replacement capacitor is installed.

Following these practices helps ensure that capacitors are installed correctly and reliably, supporting the overall effectiveness of the HVAC system.

Importance of Proper AC Capacitor Wiring Colors

Understanding and correctly applying AC capacitor wiring colors is essential for safety and efficiency. Precise wiring ensures that capacitors effectively support the start-up and continued operation of the fan motor and compressor — the two components that determine the AC system’s cooling performance.

Regular testing and strict adherence to safety protocols during installation and maintenance help prevent malfunctions and extend the system’s operational life. By applying the correct wire color code and verifying every connection, installers and maintenance technicians ensure the AC unit operates efficiently, reliably, and safely throughout its service life.