Motor capacitor location:

How to find & recognize the electric start, run, or hard starting capacitor on an air conditioner or heat pump system.

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.

Where to Find the Starter Capacitor in or on Electrical Equipment

Here we list the locations where a start or run or start/run capacitor will be found on various electric motors used in residential and light-commercial installations.

Capacitors are used in many but not all electric motors including air conditioners, heat pumps, furnace or air conditioner blower fan motors, refrigeration equipment compressors, and well pumps.

• The Capacitors are inside of the Outdoor Compressor/condenser Unit
  
  In our photo of a rather messy wiring job at left you can see two separate capacitors marked by the blue and red arrows.
  
  As you see by my blue and red arrows in our photo, the start (big round) and run (smaller oval) capacitors in an outdoor air conditioning or heat pump compressor/condenser unit are typically mounted by clips secured to the compressor body, in a location protected from the weather.
  
  Look for starter capacitors in your air conditioning equipment in the outside air handler where a starter capacitor may be used to aid compressor motor start-up, and look for a smaller motor starting capacitor on fan motors, both.
• Capacitors in the Indoor Air Handler Unit's Blower Compartment.
  
  In the air handler a start/run capacitor for the blower motor may be mounted by a clip secured to the cabinet wall or secured to the exterior of the blower assembly itself.
• The Capacitors are Mounted on the Exterior of the Electric Motor
  
  On some electric motors such as the motor shown below, one or two start/run capacitors may be spotted quite easily under those domed covers atop the motor exterior - pointed-to by my yellow arrows.

  The starting capacitor might be atop the motor under a single domed cover if the motor uses a combined start/run capacitor.

  The run capacitor will usually be attached to the exterior of the motor under a bulged cover such as in our photo below. This motor has two external capacitors: start & run (yellow arrows). You'll know which is which by examining the wiring and capacitor markings.

• The Capacitors is Inside the electric motor?
  
  Other starting capacitors on other motors may be found under the cover on the back-end of the motor - the end opposite the motor's drive shaft.
  
  2-Wire well pumps: Single phase electrical power 2-wire (120VAC) well pumps will carry a tiny starting capacitor located on or inside of the motor.
  
  Really? In some electric motors it's common to find a thermal overload switch that, if failed, might also prevent a motor from starting - don't mistake this for a capacitor. It's not. Details are
  
  at ELECTRIC MOTOR OVERLOAD RESET
  
  However, the centrifugal switch used to take the start capacitor out of the circuit when an electric motor has spun up to speed may indeed be inside of the motor body.
• The Start/Run Capacitors Inside of a Well Pump Control Box:
  
  3-Wire 240VAC higher horsepower well pumps often use a heavy-duty relay and control box to turn the well pump on and off.
  
  In these pump systems a separate pressure control switch, sensing a drop in water pressure, operates the relay in the pump control box. That relay turns the pump on as needed.
  
  Inside that control box you can find start and run capacitors for the well pump that itself maybe submersible - in the well.
  
  Some pumps use only a start capacitor while others may als employ a run capacitor to improve a poor power factor pump motor.
• The Capacitor is Nowhere: some motors don't have a starting capacitor.
  
  A three-phase electric motor typically won't have a starter capacitor, but you won't find many residential cooling systems wired for 3-phase current. You also won't see a starter capacitor on scroll-type refrigeration compressor motors.

Also see MOTOR CAPACITOR TYPES for help in determining which capacitor is which on your HVAC or other electrical equipment.

Start & Run & Dual Capacitor Specification References

• COPELAND ELECTRICAL HANDBOOK [PDF], Emerson Climate Technologies, White-Rodgers US 8100 West Florissant Avenue Saint Louis MO 63136 USA, Customer Support: email: wr.techsupport@emerson.com, Tel: 1-888-725-9797 U.S. & Canada
• Essex, Brown: "Motor Repair Supplies" (Catalog), Essex Group, Inc., 1601 Wall St., Fort Wayne, Indiana 46801, Tel: 219-461-4633, Website: www.superioressex.com, retrieved 6/20/14, original source: http://www.essexbrownell.com/uploadedFiles/Content/Products/MR%20Supplies%20Catalog-s.pdf - see pp. 86-89.
• Sealed Unit Parts Co., Inc., PO Box 21, 2230 Landmark Place, Allenwood NJ 08720, USA, Tel: 732-223-6644, Website: www.supco.com, Email: info@supcocom, Supco Catalog, retrieved 6/20/14, original source: http://www.economicelectricmotors.com/cdrom/catalogs/Supco_catalog.pdf - see pp. 2-6.
• van Roon, Tony, "Capacitors", [online article], retrieved 6/20/14, original source: http://www.sentex.ca/~mec1995/gadgets/caps/caps.html, gives a very detailed history of the invention and history of electrical capacitors beginning with van Musschenbroek's Leyden jar in 1745. This article includes
  "Capacitor Nomenclature" by Dean Huster.
• Kaiser, Cletus J., The Capacitor Handbook: A Comprehensive Guide For Correct Component Selection In All Circuit Applications. Know What To Use When And Where, 2d Ed., [at Amazon.com] C.J. Publishing (2011), ISBN-10: 0962852538, ISBN-13: 978-0962852534 - product description
  
  This book provides practical guidance and application information when using capacitors in electronics and electrical circuit design. This easy-to-use book covers the following capacitor types: Ceramic, Plastic Film, Aluminum Electrolytic, Tantalum, Glass, Mica, and others.
  
  This book also has a very comprehensive Glossary and Index. The Selection Guidelines and the Symbols and Equations sections have the answers to all of your daily application questions. This book is one in a series of component handbooks.

Examples & Sources of Start / Run Motor Capacitors

• Packard 370V 45+5 MFD Round Run Capacitor
• Supco™ 30+5 MFD 440V 440 Volt 50/60 Hz Round Motor Capacitor (typical application for Amana, Carrier, Rheem, Trane equipment)
• Supco™ 45+5 MFD 440V 440 Vol 50/60 Hz Round Motor Capacitor (typical application for Amana, Carrier, Rheem, Trane equipment)
• Supco HS6 (SPP6) Hard Start Relay Capacitor (230V) gives a starting torque boost of up to 500%. Quoting from product sales literature:
  
  The SUPCO SPP6 Super Boost hard start capacitor increases starting torque up to 500%. Features: Installs in seconds across run capacitor terminals Contains specially designed relay and large start capacitor for severe hard start problems. Applications: Room A/C units, Residential and commercial PSC A/C units and heat pumps, For all PSC A/C units from 4,000 thru 120,000 BTU's (1/2 thru 10 H.P.) Can be used on 120 thru 288 VAC units, For severe low voltage and hard starting compressors. SPP6 Specifications: Voltage: 115V - 230V. Increased Torque: 390 ounce inches. - retrieved 6/16/14 Amazon.com sales
• Supco™ Universal (broad application) Capacitor, 10 MFD at 370V

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2022-04-30 by Inspectapedia Com Moderator - start/run capacitors for HVAC blower unit fans

@Ryan Self,

It's common for HVAC blower unit fan motors to use a start/run capacitor. Those will be located in the blower cabinet, often right on the blower motor itself.

Yes those indoor blower unit fan motors and their capacitors are completely separate and distinct from the start/run caps that may be found in the outdoor condenser / compressor unit.

In your outdoor compressor/condenser unit there may be Start/Run capacitors for both the compressor motor itself and separately on/for the fan motor.

In your indoor air handler there will be a Start/Run capacitor for the air handler's blower fan.

Note that you may see two (one, the larger will be the starting cap) capacitors, one for starting and one for running the fan -
OR
you may see just one physical capacitor with 3 rather than 2 terminals - combining start and run in one device.


Shown here, a 5 uf RUN capacitor for a blower motor

Below is a dual Start & Run capacitor from Huarew, rated at 45uf (start) and 5 uf (run).

Note the 3 (rather than 2) terminals; they'll be labelled S, R, and C for "Common"

On 2022-04-30 by Ryan Self

so I have an important question. I live in hot Phoenix Arizona. I have a 2 story house with 2 Ac units. they are both heat pumps split units. they are Lennox the one downstairs is a 5 ton and the one upstairs is either a 3 or 3.5 ton unit.

my question is I know there is a run capacitor in both outdoor units because I've replaced them both several times. I would like to know if there is a run capacitor for the indoor fan motor and if so would it be located in the attic with the air handler? both units are down now. 1st the upstairs unit fan started blowing slow and then it would intermittently come on but not run long and start humming before it stopped and I had to shut down the unit.

just today on the downstairs unit it started getting hot inside but I could hear the condensing unit running outside. so I went upstairs where the return duct is at to listen if the fan was running and it is not. I turned the unit off and waited several hours as it rose to nearly 100 degrees in here and I turned it back on and nothing. I think I heard humming from the attic but I am not sure.

I am sure that the outdoor unit is working though. so now here I am with 2 units down and both have the same symptoms which is the outdoor units work but the indoor fans do not.

I had an ac guy out here last time and he visually looked at my outdoor units and said oh those must be 10 years old you are going to need 2 new ac systems and I started to hyperventilate because I am disabled and cannot afford something like that even if it was $1k it would be undoable but $12k would be impossible.

the fact that he didn't want to even look at the air handler in the attic and just jump to new units made me not trust him so I passed and went through the entire summer with just 1 unit. but now the other one is down too and I'm melting already. is there a run cap for the blowers and if so where is it please?

I saw little capacitors next to the bigger round ones inside the cabinet on the outdoor units and they look like the ones in your video but again they are outside so I assumed they are run & start capacitors for the condensing unit only...

On 2022-02-18 by Inspectapedia Com Moderator - what does this motor sound mean for my Trane?

@Jan,

That sounds like a compressor having trouble starting, possibly against high head pressure, or there can be other causes like a bad start capacitor or low voltage.

To reduce the chances for more costly damage, it'd be best to turn the system off right away, then call for repair.

On 2022-02-17 by Jan

We have a Trane dual heating and air conditioning unit. It was running but it wasn’t a steady hum, it almost sounded like a car that the motor was turning over very slowly it would Sound like rur rur rur rur

The whole time it was running. I was thinking it was the run capacitor, but the technician said it was the motor itself and charged us over $700 to replace it. I was very suspicious but the air conditioner is on the roof and you need a 30 foot extension ladder to get there and I wasn’t about to go up there myself.

What are your thoughts on a motor making that type of sound. It started fine but just was not a constant hum while running

On 2021-07-24 by inspectapedia.com.moderator

@k,

I don't know that unit specifically. So if I were faced with that capacitor location question I would follow the wires. Or grab the manual.

More examples are in the page above.

On 2021-07-24 by k

Where is run/start cap on 5T Carrier Infinity packaged unit?

On 2020-10-31 by danjoefriedman (mod)

Raheem

Please see the guidelines at CAPACITOR SIZE DETERMINATION for ELECTRIC MOTORS

On 2020-10-31 by Raheem

Good morning. I have bench grinder of size 150*16*12.7mm with a model number: .CN3215S. My question is what is the capacitor size for this motor. If i can get it asap i will be glad. Thanks you in anticipation.

On 2020-06-29 by danjoefriedman (mod)

I would start right at the motor. If there is no capacitor in or mounted on the motor then I would follow the motor wiring back from there through the various control and relays. Normally the capacitor if there's an extra Lon would be mounted quite close by. Follow the wires.

On 2020-06-29 by Todd

I have a question, how do I find a start/ capacitor on a 2014 Bryant model fan blower motor.

On 2020-06-04 by danjoefriedman (mod) - do I need a start or run capacitor and how do I tell?

Fred

There are several approaches to finding the right capacitor for your pump. The best would be to take a look at the manual for your specific pump in which the manufacturer will name in the wiring diagram the specific capacitor that they installed originally.

In general, we can tell if a capacitor is a single start or run capacitor by the number of terminals on the capacitor. If it has three terminals it's a combined start and run capacitor. If it has two terminals it is either a start capacitor for a run capacitor. Once we have decided those questions we look at the value on the existing capacitor and we can tell by the capacitor size or rating whether it is most likely to be a start which will have a bigger capacitor for a run which will have a much smaller capacitance rating in microfarads.

However it doesn't make sense to me to look at the existing capacitor on your pump if you are telling me that you already know it is the wrong one.

Instead we look at the data tag on your pump to get the pump voltage and horsepower and from that you can use the simple cables above as an alternative approach to finding the correct capacitor. But remember that the best approach is to look at the manufacturer's actual specification.

Even if you don't have the manual and wiring diagram for your pump we can usually find it if we know the pump brand and model.

On 2020-06-04 by Fred florendo

sir what capacitor is located inside the black box atop my Myers jet pump QD52S .5 HP 230 Volts....Is it starting or running capacitor...

please advise the correct uf if this is starting or running... the former owner of said pump failed to replace the original capacitor thank you

Question: can I build a submersible well pump

(Feb 21, 2014) Anonymous said:

is it possible to rebuild a submersible well pump

Reply:

Yes ... maybe; it depends on the condition of the pump casing, parts, an in my opinion, an accurate diagnosis of the trouble; at some point rebuilding is not cost effective. Indeed there are specialists (H Shreck in Poughkeepsie used to be one of them) who rebuild electric motors of all kinds.
There are also many water pumps whose design makes it quite reasonable to replace pump impellers.

So to answer your question, I dunno - it depends on what's broken.

Question: fan will start but won't keep running.

(June 1, 2014) Anonymous said:

The fan on my Conquest 80 will not stay on (interior fan). It starts and then stops after a few seconds. It was installed in 2005. Help.

Reply:

Anon,

The start capacitor is for getting a motor started, not keeping it running.

Often motors have two windings, a start winding and a run winding. Your motor's run winding may be damaged.

Or your fan motor may require a dual capacitor (start and run) or a separate run capacitor to keep it spinning.

Or your system may have a faulty control.

Question: will a hard start capacitor reduce current drawn and stop tripping a breaker

(June 7, 2014) Joel said:

I have a commercial hood & exhaust fan (120v) running in a food truck that is used for catering. We occasionally need to run off a generator (3000w) and we've found that the fan cause the generator overload to trip. The fan has been tested and observed to draw 8 amps running at full speed.

Given this, would it be possible to add a hard start kit, such as SUPCO SPP4E? Will need to confirm the motor size, just wondering if this would help.

The total draw of all items is less than 20 amps and the generator is capable of supplying 25 amps constant.

Thanks for the advice.

Reply:

Joel I think the problem lies elsewhere and needs some further diagnostics. I suspect that your total current draw is exceeding the ability of the generator - you may be running more than the fan, such as lighting, a cooler, toasters, other electrical appliances. If it were just the fan, drawing 8A, it has no business tripping the breaker.

Put another way if the problem is the fan and there are NO other appliances running, then there is a failing fan motor drawing high current, or an electrical short circuit or other unsafe condition to find and fix.

A start capacitor or a run capacitor won't change the current drawn by the motor.

...

Continue reading  at CAUSES of HARD STARTING ELECTRIC MOTORS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• BASIC ELECTRICAL TESTS for BURNED OUT COMPRESSOR MOTORS
• CAPACITOR TYPES, for MOTORS
  • CAPACITORS for HARD STARTING MOTORS
  • CAUSES of HARD STARTING ELECTRIC MOTORS
  • CAPACITOR SIZE DETERMINATION for ELECTRIC MOTORS
  • COPELAND ELECTRICAL HANDBOOK [PDF]
  • HARD STARTING COMPRESSOR MOTORS
  • HOW a STARTING CAPACITOR WORKS
  • HOW to TEST the MOTOR to ID TERMINALS
  • LOCATE the STARTING CAPACITOR
  • MOTOR CAPACITOR WIRING GUIDE
  • STARTING CAPACITOR SAFETY
  • TEST a MOTOR START or RUN CAPACITOR
• ELECTRIC MOTOR CENTRIFUGAL SWITCH or PTC PRD
• ELECTRIC MOTOR DIAGNOSTIC GUIDE
• HARD STARTING ELECTRIC MOTOR CAUSES

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