Start Capacitor Global (C) InspectApediaElectric Motor Hard Starting Capacitor Wiring & Installation
Installation Wiring Guide to Air Conditioning Compressor Motor & Other Electric Motor Start-Boost or Run Capacitors

  • POST a QUESTION or READ FAQs about installing a hard-start capacitor to get an air conditioner motor, fan motor, or other electric motor running.

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How to hook up an electric motor start or run capacitor:

This article gives electric motor start-run capacitor installation & wiring instructions for electric motor capacitors designed to start & run an electric motor such as an AC compressor, heat pump compressor or a fan motor, and how to wire up a hard-starting air conditioner compressor motor, fan motor, to get an air conditioner, heat pump, refrigerator, or freezer compressor or other electric motor (such as a well pump) going.

This electric motor capacitor article series explains the selection, installation, testing, & use of electric motor starter start and run capacitors used on various electric motors found in or at buildings such as air conditioner compressors, fan motors, some well pumps and some heating equipment.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

How to Install and Wire Up an Air Conditioner Compressor, Blower Motor, or Fan Motor Hard Starting Capacitor

A/C motor resistances © D Friedman at Make These Simple A/C Compressor Checks Before Adding a Hard-Start Capacitor

Most electrical problems in air conditioning systems are in the compressors and their relays or motor overload switches.

In a single phase (common residential A/C) compressor you can verify with an ohmmeter whether or not the A/C compressor is bad.

[Click to enlarge the image at left]

Watch out: live high voltage may be present at a capacitor, capable of giving a tremendous electrical shock even after electrical power has been disconnected at the equipment. Never work on live electrical equipment.


A fractional horsepower electrical motor should show different electrical resistance between the three terminals (Start, Run, and Common) as we illustrate just below.

Find the two highest resistance terminals.

The third one will be the common terminal.

Our example is for a Frigidaire compressor motor.

In our capacitor testing and wiring sketch at left, you note we use the letters S, C, and R to identify the usual terminals to which a start/run capacitor is wired. On many systems these terminals may be labeled so that the three leads on a start/run capacitor can be wired correctly:

See How to INSTALL & WIRE Up an Air Conditioner Compressor, Blower Motor, or Fan Motor Hard Starting Capacitor.

Electric Motor run speed side note: Incidentally while most electric motors are marked with a data tag indicating the motor run speed (in RPMs) it's worth noting that the number of run coils is what determines the run speed of the motor. Two-coils marks a motor that runs at 3450 rpm (3600 rpm "nominal"), while 4 coils marks a 1725 rpm motor. (120V, 60 cycle/sec x 60 sec/min = 3600 rpm).

Electric motor diagnostic procedures are given in detail

Simple Relay and Hard Start Capacitor Wiring Instructions - Example 1

Hard start capacitor wiring (C) D Friedman Sealed Parts Co.

Relay and hard start capacitors such as the Starter Pow-R-Pak sold by Sealed Unit Parts Co., can be installed with no wiring changes to the original system whatsoever. Quoting from Part No. SPP-5, a relay and hard start capacitor sold by that company:

Connect the two wires from the SPP-5 in parallel with the [existing, already installed] run capacitor (one wire each side) without removing any original wires.

Use special "piggy back" terminal of the SPP-5 if all the run capacitor terminals are being used. [Install only on PSC units equipped with run capacitor.]

Simple Relay and Hard Start Capacitor Wiring Instructions - Example 2

wiring diagram for a motor starting capacitor

Here are some sample capacitor installation instructions for adding a motor starter capacitor to an air conditioning compressor motor - taken from the product package for a relay and start capacitor intended for use on a refrigerator or freezer. Similar starter capacitors are available for air conditioning compressors.

[Click to enlarge any image]

  1. Remove the power supply cord from the electrical outlet - in other words, be absolutely certain that electrical power has been turned off to the equipment being serviced.
  2. Remove the old starting relay, leaving the old overload protection in place.
  3. Push the wire with the one single pin terminal onto the "start" terminal of the air conditioning compressor. (See the wiring diagram above).
  4. Push the other wire with the pin terminal onto the "run" terminal of the air conditioning compressor.
  5. Connect the line from the old starting relay to the spade terminal on the "run" wire (insulating sleeve).
  6. Restore electrical power

Start / Run Capacitor Mounting Positions

Starting capacitors in place on an air conditioning compressor (C) InspectAPedia.comStart/run electric motor capacitors can be mounted in any direction or position. However there are some other capacitor mounting considerations that can affect capacitor life: basically you want to minimize the capacitor's exposure to vibration and heat.

As Afacp points out, ..."the temperature on the surface of the capacitor cannot exceed, even under the worst conditions, the maximum permitted temperature.

It is advisable to make an experimental measurement of the temperature reached by the capacitor under the working conditions in the final application and after the thermal equilibrium has been achieved."[2]

Watch out: Air Conditioner Motor Starting Capacitor Safety warnings:

When testing a compressor, one must discharge the capacitor first! It'll otherwise have enough power stored on it to be at least very painful. (Author and others have been zapped!)

Some systems will automatically discharge the capacitor, but shorting its leads [to ground] with a screwdriver (after verifying that the power's off) is a safe way to ensure that you won't get shocked. Motor starting capacitors can hold a charge for days!

If oil has leaked out of a capacitor: Don't touch any oil that leaked out: old capacitors may contain PCB oils, an extremely carcinogenic (cancer causing) material which require special disposal.

Once the capacitor has been discharged (as described just above), then it can be tested with a multi meter. Either use the meter's built in capacitor test function, or use this trick: Charge the capacitor by using the sense current the meter puts out when set to ohms. You should observe a rapidly rising resistance before the meter indicates over range/infinity.

Disconnect the test leads, and switch over to volts. Then, reconnect the test leads. A voltage reading should be observed, approaching zero.

If the capacitor doesn't hold a charge, or the resistance reading never approaches infinity, it probably needs replacement.

Also, the capacitor may be defective if the compressor hums but does not start. Visual inspection may reveal it to be bulged, or have a blown out safety plug.

Start / Run Capacitor & Fan or Compressor Motor Wiring Color Codes & Connections

On 2017-07-09 by Brian Render

I'm replacing my run capacitor in my air handler. I forgot to mark the wires I took off. I have 4 wires. A blue, a black, a yellow, and a brown. Brown , and yellow come from the motor. Red, and black go to a control box. What goes where?

On 2017-07-09 by (mod) Typical color codes & wiring connections for an air handler blower fan or a compressor/condenser fan & compressor wires


RE: wiring up an HVAC air handler fan motor capacitor:

You reported four but listed five wirres in your air handler and that were connected to the run capacitor:

BLACK - to a control box
YELLOW - from motor
BROWN - from motor
RED - to a control box - typically wires to C

The reason you can spend hours looking at online chats about HVAC start-run capacitor wiring without finding a single absolutely-right guide to capacitor wiring color codes is that the service techs who make these repairs don’t want to give an answer that kills someone or burns up their equipment.

Watch out: touching live voltage can kill you. Turn power off and discharge any capacitors before touching anything. A capacitor can store a charge that can hurt you or worse even after power has been turned off. If you’re not sufficiently trained and informed about electrical repairs hire someone who can do the work properly and safely.

The tech will typically use an insulated screwdriver to short the F or H terminals to the COM terminal to discharge the cap.

While there are common capacitor wiring color conventions that I will cite below, the actually-correct wire colour match to fan motor terminals, wires, and capacitor terminals may vary by motor brand, age, model and application. But there are steps that can help sort out which wires go where.

Next time, remember to tag each wire with an ID and write down its connections before removing wires from their connections on electrical equipment.

Watch out: It's safest to take a look at the wiring diagram on the equipment itself - you can follow them to the marked-terminals on your start or run capacitor. There are also some simple VOM tests that can help identify motor terminals.

Look at the wiring diagram for your specific HVAC equipment and find the capacitor where you’ll see its wires and their identities. You should see a wiring diagram glued to the inside of the air handler cabinet or to the inside of the blower compartment door.

You can also obtain a wiring diagram for your air handler brand, model, serial number from the manufacturer, or give us that information and we’ll help dig it out.

Now with all that scary arm waving done:

HVAC service technicians are invited to CONTACT us to improve these general color codes & wiring tips for start/run capacitors, dual capacitors, and fan or compressor motors. We are happy to cite, credit, and refer readers to expert sources & technical content contributors.

InspectAPedia is an independent publisher of building, environmental, and forensic inspection, diagnosis, and repair information provided free to the public - we have no business nor financial connection with any manufacturer or service provider discussed at our website. We do not sell products nor services.

Website content contributors whether it is just a small correction or an in-depth article series (which of course invites more search engine attention), are, if they choose, cited, quoted, and linked-to from the appropriate additional web pages and articles - which benefits us both. Those who wish to remain anonymous can also do so.

Blower fan motors and other fan motors may have what look like extra wires, not all of which may be in use, depending on the fan speeds required.

HVAC Capacitor Wiring Number of Terminals & Wiring Color Codes & Terminal Identification COdes

Usually the following wire colors will connect to the terminals or sources or controls we list below - you’ll see data like this (though the colors may be different) on the wiring diagram for your own equipment.

Watch out: Your equipment’s wiring diagram and what its manufacturer tells you will be the final authority on which connections are correct.

HVAC Capacitor Wiring Color Codes & Connections - Basics

Wire Color Typical Connections
Compressor/Condenser Unit
Typical Connections
Blower Assembly / Fan

Power source. Usually connects to C or Common terminal on the Capacitor.

Compressor contactor relay T1 to C on the Compressor motor terminal

Black also wires from Compressor Contactor T1 to T5 on Start Relay
Black also wires from Compressor Contactor T1 to Power terminal on Outdoor Fan Motor

Air handler unit blower fan motor to T1 terminal on contactor relay

Power from a fan relay to the fan motor

Red - power source

Power source. Usually connects to R or Run terminal on the Capacitor.

Compressor contactor relay T2 to R on the Compressor motor terminal

Power from fan relay to fan motor will typically connect to the T2 terminal on the Contactor relay.

For multi-speed fans red = low speed motor terminal


Two blue low voltage wires to operate the contactor relay magnet

Often: Compressor R or Run terminal to S on the Compressor Start capacitor
Compressor R or Run terminal to R on the Compressor Run capacitor

Power for medium speed motor terminal

Fan motor to capacitor (motor start terminal)

Connects fan to the F or FAN terminal on the capacitor to fan motor

Fan motor to the capacitor (from the motor start terminal)

Connects the Fan motor to the F or FAN terminal on the capacitor for the fan motor

Brown + White

Same use as white wire, C on capacitor to T2 on contactor

Not used when using a dual start/run cap

Same use as white wire, C (common) on capacitor to T2 on contactor

Not used when using a dual start/run cap

Green Ground wire in nearly all systems  

From power terminal on fan motor to C or COM on the capacitor

Compressor contactor relay T2 to C or COM or RC connector on the Run or Start/Run Capacitor

Outdoor Fan Motor to C or COM or RC connector on the Run or Start/Run Capacitor

For multi-speed fans, orange is medium-low speed

S terminal on Compressor to HERM or H on the Run or Start/Run Capacitor

May be ground or neutral.

Fan motor direction reverse to counterclockwise if grounded - connect purple to yellow to reverse.

Connect from fan to the COM terminal on the capacitor


Compressor contactor relay T2 to R on the Compressor

Start Relay T1 to C on a separate Start Capacitor
& when separate start & run caps are in use,
Separate Start Capacitor C to C on Run Capacitor


Compressor to the H or HERM terminal on the capacitor

Often: Compressor Start Relay to C on the Compressor Start Capacitor

From a fan motor controls the medium speed motor
White Common wires connect to the grounded (neutral ) side of power source Common wires connect to the grounded (neutral ) side of power source


Electric motor speed taps: typical: L2 connects to

Black = high speed

Blue = medium speed

Red = low speed

Purple to purple = rotate clockwise

Purple to yellow = rotate counter-clockwise

Dayton Electric Motor Wiring Diagram [PDF], Dayton Electric Mfg. Co., 5959 W. Howard St., Niles IL 60714 USA, retrieved 2017/07/09, original source:

Start & Run & Dual Capacitor Specification References

Motor run capacitor by Dayton - oval, 2 terminal (C) InspectApediaAt left is a simple two-terminal run capacitor.


Continue reading at EXAMPLE of CAPACITOR REPLACEMENT or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see MOTOR CAPACITOR TYPES for photos identifying the terminals on start and run capacitors and indicating which wires are connected to which terminals.


Or see this

Article Series Contents

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Publisher - Daniel Friedman