Dayton dual motor run capacitor, # 6FLP0, 440C, 35/3 MFD, 4 1/8" oval capacitor (C)

Electric Motor Starting & Run Capacitor Types
Installation Guide to Electric Motor Start-Boost or Run Capacitors

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Types of electric motor start & run capacitors:

This article explains and gives an identification guide to types of electric motor capacitors: motor starting capacitor, motor run capacitor, dual-run capacitors, and hard start capacitors used on electric motors such as air conditioner & heat pump compressors, fan motors, some well pumps & some heating equipment motors.

We explain and illustrate how to recognize different types of motor capacitors and how to determine the use or identity of the different connector terminals on the capacitor.

This air conditioning, heat pump, or other electric motor repair article series discusses the selection, installation, testing, & use of electric motor starter start and run capacitors designed to get a hard-starting air conditioner compressor motor, fan motor, refrigerator, or freezer compressor or other electric motor (such as a well pump) going.

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.

Types of Electric Motor Capacitors including Air Conditioning Compressor or Other Electric Motor Starting Capacitors

Start Capacitor Global (C) InspectApediaHow to tell what type of capacitor is installed on your motor - difference between a starting capacitor, a run capacitor and a dual run capacitor

Capacitors are electric devices that, by storing and then releasing an electric charge. In many electric motors there are two types of capacitors present, a starting capacitor and a run capacitor.

Dual run capacitors support the operation of two motors from a single advice, such as an air conditioner compressor motor and a fan motor. Hard start capacitors give an extra large starting boost to hard-starting electric motors, possibly extending their service life.

[Click to enlarge any image]

For example, air conditioner and heat pump compressor motors (and lots of other electrical motors) that run on two-phase (220V) or single phase (120V) electrical power include a capacitor in the start circuit to help get the motor spinning and a capacitor can be put into the "run" circuit of the motor as well to increase motor efficiency.

Start Capacitors: Get a Motor Spinning

A starting capacitor such as the Global universal start capacitor shown at above-left has the single job of giving a large voltage boost to give extra turning force or torque to a motor to start it spinning in the right direction by providing about double that nominal system voltage.


A start capacitor does not keep at the job once the motor is operating. The rating on a starting capacitor will include a high MFD number and the operating voltage range. Temperature ranges and other data may also be provided on all caps.

AmRad Turbo 200 allows multiple choices of capacitor MFD outputs (C) InspectApedia.comStarting capacitors will be of much higher microfarad uF or MFD rating than run capacitors. As you may notice from the forest of connection points on the top of the round capacitor shown above, there may be multiple wiring connections depending on the capacitor's use and features - connections we explain in this article series.

The start capacitor rating or power in microfarads (uF or MFD) required depends on the size, voltage, and other properties of the motor that it's starting.

Some manufacturer's capacitor models such as AmRad's MARS universal Turbo All-in-One capacitor (shown here) as many as six terminals will use color coding combined with markings on a label wrapped around the capacitor to indicate the uF rating of each connector, such as 5 uFD - White, 2 uFD - Green.

By using a combination of jumper wires the installer can generate and choose among up to 200 different uF ratings for her specific application.

Typical ranges for electrical motors likely to be found in a home (air conditioning compressor motors, fans, pumps) are from around 150 to 480 MFD and at voltages of 120-240-440. Prices for a start capacitor range widely from under $10. U.S. to over $100.

Watch your prices when buying a universal or any other replacement capacitor. I have seen the AmRad Turbo 200x universal motor run capacitor at about $10., $55., and $85. U.S.D.

If the start capacitor has failed the symptom is that the motor won't start. If either or both start and run capacitors are defective the motor may try to start but will hum and won't keep running. You may hear a compressor or fan motor humming or observe that it's getting hot.

Watch out: If you observe a humming electric motor that is not starting we suggest that to avoid damage you turn off the system while waiting for repairs.

Run Capacitors are Used to Improve Electric Motor Power & Efficiency

Motor run capacitor by Dayton - oval, 2 terminal (C) InspectApedia

Function of a run capacitor

Once the motor has started, a run capacitor may be used to help the motor retain full power, providing 1.5 x the nominal system voltage and varying as needed depending on the load on the motor.

Copeland explains the run capacitor as follows:

Run capacitors are used on compressors to improve efficiency, raise the motor’s power factor, and lower noise.Run capacitors are continuously in the operating circuit and are normally of the metallized film type. They are manufactured in oval or round cans. - Copeland Electrical Handbook p.A7.

The oval motor-run capacitor sold by Dayton (made in China) and here is the simplest two-terminal run capacitor you'll encounter and is sold in a range of MFD ratings, voltage ranges, and in oval and round shapes.

This is a single-purpose capacitor with one uF or microfarad rating intended to support one electric motor. Below you'll read about more-complex capacitors that can provide both start and run support or that can provide run assistance for two different motors at two different capacitances, such as a compressor motor and a fan motor.

In some old-school class views adding a run capacitor is similar to making two-phase out of one-phase electricity and is a common practice on air conditioners.

What these folks really are saying is that "With capacitive reactive power of about 75% of the nominal power of the motor, the comparison of power is slightly lower than that of a three-phase motor of equal size." [2]

Technical notes: Single phase electric motors such as those used in air conditioner compressors and fan motors contain two different stator windings: an auxiliary starter winding fed by an electric capacitor and a main run winding fed by the principal electrical circuit.

The auxiliary starter winding is used to provide an extra boost (and proper direction - ELECTRIC MOTOR RUN DIRECTION) to get the motor spinning at start-up.

Three phase electric motors do not use start/run capacitors.

Definition of PSC, CSR and CSCR capacitors

Electric motors that use start/run capacitors may be PSC (permanent split capacitor) and CSR / CSCR (capacitor start, capacitor run) designs.

Unlike a PSC motor, a CSR/CSCR motor must also have a starting relay that will cut the start capacitor out of the electrical circuit once the motor has gotten up to run speed.

The run capacitor then remains in the circuit to keep the motor spinning properly.

Definition of a PTC Start Assist Resistor

The PTC (Positive Temperature Coefficient) resistor is used for applications where high starting torque is not required. The PTC resistor is connected in parallel with the run capacitor, placing it in series with the start winding (Figure 6). The PTC has a low resistance when it is cold. When the motor starts, the low resistance causes a large current to fl ow through the resistor.

The current drawn by the resistor is out of phase with the current drawn by the motor windings, and this provides the torque to start. As soon as the resistor draws current, it begins to heat, and the positive temperature effect of the resistor causes it to rapidly increase its resistance. By the time the motor reaches full speed, very little current is drawn by the resistor.

Although it remains connected to the motor circuit, it has no significance in the operation of the compressor.  - Copeland Electrical Handbook p.A7- A8.

Dual run capacitors operate two different electric motors at once

Dayton dual motor run capacitor, # 6FLP0, 440C, 35/3 MFD, 4 1/8" oval capacitor (C) Dayton dual motor run capacitor, round (C) InspectApediaA dual run capacitor for electric motors combines two different microfarad-rated (MFD/uF) capacitors in a single housing or container such as the Dayton capacitor examples shown at left, and provides run support for two different motors.

In a common air conditioning application these would be the compressor (marked Herm), and the compressor/condenser unit fan (marked F or Fan).

To spot a dual run capacitor that operates both the compressor and the fan motor, look for three terminals on the capacitor: one will be marked "common" or may be marked with a red dot to indicate that role.

A dual run capacitor will always have [at least] three wiring terminals - as you can see on both examples above, while a simple single-use "run" capacitor will have only two terminals providing a single MFD capacity.

In contrast with a dual run capacitor that serves two motors, single-run capacitor serves just one motor.

As we explain next, usually you'll find that on a typical HVAC capacitor you have multiple ways to identify the connecting terminals or clips or "tines":

How to Identify Which Connecting Terminal is Which on a Dual Run Capacitor

AMRAD Engineering Inc. capacitors (and some others) add a color code to help identify the correct capactior C F Herm terminals (C) On a dual run capacitor the terminals will be marked "C", "HERM" and "FAN". Check the markings, color code and number of connecting clips at each of the three terminals on your capacitor.

Shown here, color coded terminals on an AmRad Engineering Run Capacitor, part # USA2236. The individual capacitor data label will give its rating such as 45+5 MFD 370 or 440 VAC 50-60 HZ. AmRad's product code for the part shown is #3460.

[Click to enlarge any image]

How to read the MFD or MicroFarad rating numbers on a dual run electric motor capacitor

The rating on a dual run cap will include two MFD ratings and a voltage range, such as 45/5/440 expressed in numbers separated by a slash and interpreted as follows:

The particular starting capacitor to be purchased is matched to the horsepower range and voltage of the compressor or motor being repaired.

Many motor starter capacitors to support a pretty wide range of motors. For example our sample capacitor was rated for use on 115V electric motors rated from 1/12 horsepower to 1/2 horsepower.

Prices for typical air conditioner compressor starter capacitors range from around $10. to $50. U.S.

Hard-start start capacitors or "booster" capacitors?

Photograph of  This new compressor was placed directly against
a brick wall. One third of its condenser coil cooling ability was blocked.If your air conditioner has stopped running (see LOST COOLING CAPACITY) , a possible problem is the failure of the starting capacitor found on the outside compressor/condenser unit.

If that unit has electrical power but the compressor and/or its cooling fan are not running, one of the components to check (and that is easy to replace) is the starter.

When an electrical motor is having trouble starting, such as an air conditioning compressor motor (see HARD STARTING COMPRESSOR MOTORS), blower motor, a refrigerator motor or a freezer motor, or even a fan motor, the repair technician may install a simple and inexpensive hard-start capacitor.

The starting capacitor is a simple electrical device which can give an extra voltage jolt or "boost" to get the hard-starting motor spinning.

The capacitor in our page top photo is oval in cross section, but most replacement and many newer air conditioner motor starting capacitors are simply cylindrical in shape (photo at left).

We give capacitor wiring details at HOW TO WIRE up a START CAPACITOR

These dual run caps are available at Grainger ( as well as electrical and HVACR suppliers. Dayton Electric Manufacturing company, 14441 W Il Route 60, Lake Forest, IL 60045 (847) 535-1000, produces electric motors, fans, pumps, electric capacitors, audio capacitors, tools, even hand trucks.

Examples & Sources of Start / Run Motor Capacitors & Dual Capacitors - Capacitor Number Decoding Charts

Dual capacitor for AC Condenser Unit indicating the connector functions (C) InspectApedia.comShown here, a 50-5 uF dual run capacitor typical of those use on air conditioning compressor/condenser units.

We have marked the identity of the three connectors found on the capacitor top. You may see identical-looking capacitors with labels indicating different manufacturers such as AmRad, Jard or MARS (Motors & Armatures). This is a MARS2 328PSH37N31ASZ9 # 12755, 50 uF + 5.0 uF 370VAC dual run capacitor.

Watch out: be sure to check the identification and use of the connectors on your replacement start / run or dual run capacitor. Some models like the MARS brand 5-97.5MFD Turbo 200X Universal Capacitor (370/440V) can have as many as six terminals on the capacitor top. Most-likely, in repairing an air conditioner condenser unit you will be using just three of them.

Also see HOW TO WIRE up a START CAPACITOR for details about wiring up a capacitor to a motor.

[Click to enlarge any image]

Question: What's the Difference between dual capacitors and single capacitors?

CDE SFS44S45-4K475E Dual Capacitor in a Lennox Compressor Unit (C) Hi guys. Watching all of these videos online about no start a/c compressor fans or motors they all change the dual run capacitor and the unit starts.

Are they really run capacitors, start capacitors, or both. Is the 45 for the compressor, and the 5 for the fan to jump start the starter windings, or is 45 the start for both motors, and the 5 for running of both motors. Nobody seems to clarify those numbers.

No matter how many videos that I watch, they always call it a dual run capacitor, and I never seen them change a single capacitor that is just a start capacitor. Just don't get it. Thanks.

- Anon by private email 2017/11/24

Shown here: a CDE (Cornell Dubilier Electronics) Dual Run Capacitor. For this run capacitor, CDE # 100335-48 rated at 45-4uF +/- 10% 440VAC 50/60 Hz the two microfarad or MFD ratings are 45 MFD and 5 MFD (the higher number for the compressor motor the lower number for the fan motor)

Reply: how to identify your capacitor and how to decode its number markings.

Thanks for asking, I agree that these capacitor types and names can be confusing.

Electric motors and how they run and use capacitors vary:

1. Some electric motors use no capacitors at all. We'll skip those for now.

2. Other electric motors require a capacitor to get the motor spinning (the start capacitor) and another capacitor keep the motor spinning after it's up to speed (the run capacitor).

First Let's Summarize Three A/C Capacitor Types

Start capacitor - start the motor spinning - we need more of a kick to start up a motor that's not moving. Typical start capacitors on equipment you'll typically see are in the 70 to 120 uF or microfarads. It's giving the motor a big kick in the patuchka to get it started up.

Your Lennox XC15 does not sport a Start Capacitor.

Run capacitor - keep the motor spinning - A typical run capacitor doesn't need so much oomph as the motor is already spinning, so it'll be in the 7-9 uF range. It's giving the motor just a little extra torque force to keep the motor spinning.

The term "dual capacitor" can be confusing because there are two kinds of "dual capacitors":

Dual Start/Run Capacitors - three- lead capacitors to combine "start" function and "run" function in a single device. So a dual capacitor for a fan motor will have three leads,

  1. Common - incoming power
  2. Start - power used just while the motor is starting up
  3. Run - power used while the motor is running

I like to call those "dual function" capacitors as they combine two functions: start, and run, in one physical device. They would not work any differently than if two physically separate capacitors were installed, one for starting and one for running, but in a single device less space is needed.

Your Lennox XC15 does not sport a dual start-run Capacitor. Recapping notes given earlier in this article,

Dual Motor Run Capacitors - three lead capacitors to combine the "run" function for two physically separate motors in a single device. So a dual capacitor for an air conditioning condenser unit will have three leads

  1. Common - incoming electrical power
  2. F - for Fan - to run the fan motor
  3. H - for HERMetically sealed compressor motor - to run that big compressor motor

I like to call these dual motor capacitors since the same cap runs two different motors.

This is the type of capacitor found on your Lennox XC-15 condenser unit. So if you search for "Where is the start capacitor on a Lennox XC15" you'll find only references to this dual motor capacitor.

Reader follow-up: What Type of Capacitor is Installed in my Lennox Condenser Unit?

Lennox XC15 Condenser Unit Wiring Diagram (C)  showing capacitor connectionsThank you for your quick reply. But I still have a problem. The system is a Lennox xc15-036-230-04.

The capacitor is a 45-4 uf. At 440 ac.

The way the schematics read, there is a dual capacitor with wires going to both the compressor s winding and the fan motor. The fan motor [ on my XC15 ] does not have C H F on it but it does have three wires. When I look up those 45-4 numbers on the internet, it comes back as a dual run relay.

Unless s stands for stator, I just don't get it. A start capacitor is supposed to have high microfarads. This seems like the run of the mill dual run relay. But why does the h terminal on the capacitor go to the s on the compressor motor.

I thought a run capacitor would not be in the s circuit of a compressor motor. And since the fan motor has no winding letters, I don't know if that 4 is in the start or run windings. Thanks. It is just very conflicting.

Reply: yours is a dual run capacitor

On your photo of the wiring diagram shown above, one that you took from inside of your Lennox XC15 condenser, unit I've marked the electrical wire connections between the capacitor and the compressor and fan motors.

[Click to enlarge any image] We also provide a complete copy of the wiring diagram for the Lennox XC15 series condensers at LENNOX XC15 SERIES SPLIT SYSTEM CONDENSER UNIT WIRING DIAGRAM [image file]

Where to Find the Condenser Unit Capacitor

Where to find the various parts of a Lennox XC15  air conditioner condenser unit - at - Cites & refrers to Lennox IndustriesFirst we have to look in the right place. C H F will be marked on the start/run capacitor, NOT on the fan motor and NOT on the compressor motor.

If you click to enlarge the image shown here, (adapted from the Lennox XC15 Installation Manual found at at LENNOX Industries Air Conditioners, Furnaces, Heat Pumps , Manuals, Guides) you'll see the capacitor's location marked in the unit's left side. The letters C F H are marked on the top of the capacitor by its terminals.

Below in these notes I'll explain two other ways to figure out which terminal on the dual run capacitor is which and to what wire each of these terminals should be connected.

Even before decoding the markings on your capacitor we can be pretty sure this is a "run" capacitor not a "start" capacitor because of its comparatively low 45-4 MFD rating. That's 45 microfarads or 45 MFD for the compressor motor. If this were a start capacitor it's rating would be more likely in the 180-200 MFD range.

Decode the Data Tag on your Capacitor from CDE: this is a run capacitor.

The CDE capacitor # 1--335-48 is produced by Cornell Dubilier Electronics (CDE)
45-4uF +/- 10% 440VAC 50/60 Hz gives the two microfarad or MFD ratings 45 and 5 (the higher number for the compressor motor the lower number for the fan motor)

SFS44S45-4K475E gives the capacitor model

SF-capacitor series

S - case type (Round)

44 - 440VAC voltage rating (maximum)

S - case material (steel)

45-4K - the two MFD ratings for the capacitor

475 - case height (or length) 4.75"

E - variety, where yours = Dual 2,3,4 70 ºC

The C H F indicators as I noted earlier, will be marked not on the fan motor but rather on the capacitor itself, usually on its top surface next to the connectors but on some capacitors the terminals may be identified by imprints on the sides of the capacitor on a label just below the connector.

F to Fan: So on the Cap the terminal marked F would go to the fan motor - in your wiring diagram showing the capacitor that'd be the purple wire.

H to Compressor: And on the Cap the terminal marked H (as in HERMetic Compressor) goes to the compressor - that'd be the yellow wire from H on the capacitor to S on the compressor.

C to Common: And on the Cap the terminal marked C (Common) gets the incoming red wire that's supply voltage.

At CDE this capacitor is Part No. 100335-48 (and is available from some online vendors like

I found replacement units of the same range for sale from many vendors.

Here is an excerpt from a similar product spec sheet for CDE SF type Motor Run Capacitors

Type SF dual rated oil filled motor run capacitors made with self-healing metallized polypropylene film are commonly used in air conditioning, motors and compressor applications.

The dual ratings in a single can provide two capacitors - one may be used as a fan capacitor and the other as a compressor or motor run capacitor.

Three terminals allow one terminal to act as a common while the other two are connected to the individual capacitors.

Trust the wiring diagram.

Here is a typical SF type capacitor specification sheet:

Sorry, I know this can be confusing. Also see this service guide for your Lennox condenser unit:

Readers needing service manuals for other heating or cooling equipment can find them at MANUALS & PARTS GUIDES - HVAC - home - Master Index to All Brand Names & A-E HVAC manuals, wiring diagrams, installation and repair guides


Continue reading at LOCATE the STARTING CAPACITOR or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see this

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