Electric motor start-run capacitor FAQs:

Questions & answers about choosing, installing, & troubleshooting starting capacitors & run capacitors used on electric motors.

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.

These electric motors use a capacitor to start and run the motor efficiently.

Electric Motor Starting Capacitor or Run Capacitor FAQs

These electric motor start or run capacitor questions & answers were posted originally

at CAPACITOR TYPES, for MOTORS - be sure to review that article

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: whenever an electrical component has failed it is important to understand whether the failure is endemic to the component itself, or whether the component failed because of a problem somewhere else.

Watch out: also for a failing compressor motor. An early symptom of a failing A/C or heat pump compressor is hard starting. Installing a capacitor may work, for a while. When the circuit breaker trips or fuse blows at compressor start-up, we suspect a bad compressor motor.

[Click to enlarge any image]

On 2022-09-26 by InspectApedia-911 (mod) - capacitor start motor starts then pops the breaker

@Anonymous,

It sounds like the motor is shorting out when it gets up to speed that could be a short in the Run winding.

On 2022-09-26 by Anonymous

1.5 HP capacitor start motor starts, then after a few seconds pops the breaker. Is this indicative of a capacitor problem or that of the motor itself?

On 2022-04-29 by Ian

@Inspectapedia Com Moderator, Many thanks .

On 2022-04-28 by Inspectapedia Com Moderator - old English Electric 1/4hp single phase AC motor

for other readers: below is a photo of an English Electric single phase electric motor as for sale on ebay at a current auction

Its specifications given by the vendor include the following:
ENGLISH ELECTRIC
INDUCTION MOTOR
SIZE NO.: D213D/1357
HP: 3
PHASE: 3
RPM: 1730
CLASS: E
VOLTS: 220/440
AMPS: 8.6/4.3
RATING: CMR

For an induction motor, in essence you can reverse its run direction by swapping the wires on its start winding.

More about electric motor wiring is at

MOTOR CAPACITOR WIRING GUIDE

and

ELECTRIC MOTOR DIAGNOSTIC GUIDE

On 2022-04-28 by Inspectapedia Com Moderator

@Ian,

ELECTRIC MOTOR RUN DIRECTION https://inspectapedia.com/electric/Electric_Motor_Direction.php

Explains run direction in electric motors, will help you identify what types of motors can have their run direction reversed, and which wires are usually swapped.

On 2022-04-28 by Ian

I have an old English Electric 1/4hp single phase AC motor, no capasitors just a start winding and run winding can i reverse rotatin of motor if yes How any help much appreciated.

On 2021-06-06 by mak.church (mod) - hot tub motor hums for a second then shuts off

@david, Please see the following article which refers to a hot tub motor hum:

HOT TUB, SPA, WHIRLPOOL PUMP REPAIR

Let us know if you have additional questions.

On 2021-06-05 by david

hot tub motor hums for a second then shuts off i have replaced both capacitors the jets will work but after that cycle it won't come on

On 2021-03-07 by danjoefriedman (mod)

@keith moore,

I guess that's possible if there's a bad "Run" capacitor, but more likely in my opinion is another cause such as

- a failing motor bearing
- dirty, poor contact at the brushes
- damaged stator or commutator
- damaged motor winding that opens when up to speed

On 2021-03-07 by keith moore

motor runs at slower speed, it is arcing at brushes, brushes OK, is this a capacitor problem?

On 2020-12-14 by danjoefriedman (mod) - can a grinder run without a starting capacitor

Sione

If an electric motor is designed to use a starting capacitor it will not start without one.

On 2020-12-14 by Sione Takapautolo

can a grinder run without a starting capacitor.what will be a further problem caused .

On 2020-12-08 by danjoefriedman (mod)

Thank you very much for that follow-up Patrick, that will help other readers.

It's possible that a binding rotor or failing bearing relate to and even kill off a starting cap.

Or the starting capacitor was never the real problem - which is often the case: we add a start cap to get a failing motor running again -for a short time until it fails hard.

On 2020-12-08 by Patrick

Update: I ended up taking the motor to a local electric shop. The scratches I found on the windings were actually the problem. The motor is dead (or could be rewound but given the cost 500+ there would be no point). Interesting how a classic symptom of failing capacitor (motor does not start by itself) can end up being something else!

On 2020-08-22 - by (mod) - find the correct capacitor for a Korean-made Fan motor

Hi Lauren,

The 25/85/21 is about as close as you might get unless you identify the fan brand and model and then contact the manufacturer for an original replacement part.

Where in Korea ? ( lived there for more than a year in the 1960s and have an abiding respect and affection for the country and the Hanguk.)

There are a great many manufacturers of motor capacitors in South Korea - some are listed below.


Eppscore Co., Ltd.
(1.3)
Supplier From Kyunggi-Do, Seongnam-Si, South Korea (Republic Of Korea)
Super capacitor.

Supplier Of Capacitors

Inquire Now Add to FavoritesDec-15-18

Yu Chang Electronics. Co. Ltd
(1.3)
Supplier From Bucheon, South Korea (Republic Of Korea)
Metallized film capacitor(box type).

Supplier Of Capacitors

Inquire Now Add to FavoritesDec-15-18

Eastone Corp.
(1.3)
Supplier From Seoul, South Korea (Republic Of Korea)
Low voltage power factor capacitor, AC motor capacitor for air conditioner, AC motor capacitor for washing machine, ac motor capacitor for pump, capacitor for lighting, fan capacitor, metallized film for capacitor, DC link capacitor, medical instruments capacitor, snubber capacitor, noise suppressor capacitor for vehicle.

Supplier Of Capacitors

Inquire Now Add to FavoritesDec-15-18

Sungnam Electrics Ind. Co., Ltd.
(1.3)
Supplier From Sungnam, Kyunggi-Do, South Korea (Republic Of Korea)
Rubber bung for electrolytic capacitors, rubber gasket for batteries and lighting, seal sheet for super capacitors, washer / base plate, capacitor.

Supplier Of Capacitors | Gaskets

Inquire Now Add to FavoritesJun-01-20

Sap People Co., Ltd
(1.3)
Supplier From Hwaseong, Jeongnam-Myeon, South Korea (Republic Of Korea)
LED Light, customer specification LED Light.

Supplier Of Capacitors | Light Emitting Diode

Inquire Now Add to Favorites13 Capacitors SuppliersShort on time? Let Capacitors sellers contact you.
Name
Email
Phone (e.g. +1-111-111-9999)
Provide details about your capacitors buying requirement so suppliers can contact you with their quotes.
Dec-15-18

Taeyoung
(1.3)
Supplier From Kyunggi, Wonmiku Bucheon, South Korea (Republic Of Korea)
Aluminum, film capacitor.

Supplier Of Electronic Capacitors | Aluminum

Inquire Now Add to FavoritesDec-15-18

Future Trading
(1.3)
Supplier From An Yang, South Korea (Republic Of Korea)
PP film, epoxy resin, capacitor.

Supplier Of Plastic Items | Capacitors

Inquire Now Add to FavoritesJan-02-21

Siddiqui Nadeem
(1.0)
Supplier From Songpa-Gu, Seoul, South Korea (Republic Of Korea)
Quartz, Handmade Sink, Ac Capacitors, Copper And Aluminum Pancake For Ac, And Other.

Supplier Of Quartz | Electric Components | Non Stick Cookware | Kitchenware & Cooking | Sinks, Washbasins, Countertops | Capacitors

Inquire Now Add to FavoritesDec-15-18

Parts Solution
(1.3)
Supplier From Anyang, Kyungki-Do, South Korea (Republic Of Korea)
Fire extinguisher, capacitor, resistor, tantal.

Supplier Of Fire Extinguishers & Products | Capacitors | Electric Resistors

Inquire Now Add to FavoritesDec-15-18

Woosoo Global
(1.3)
Supplier From Anyang, Kyunggi-Do, South Korea (Republic Of Korea)
Chip-capacitor, chip-resistor, temperature controller, timer & counter, laser diode, H.V. capacitor.

Supplier Of Temperature Controllers & Indicators | Electric Resistors | Capacitors | Electronic Timers | Diodes

Inquire Now Add to FavoritesDec-15-18

Cabot Micro Electronics
(1.3)
Supplier From Seoul, South Korea (Republic Of Korea)
Semi conductor material.

On 2020-08-22 by Lauren

High velocity metal floor fan (I live in Korea, so higher voltage all around) These capacitors are easily found, but do the numbers I've circled in yellow have to be the same?

I've seen 40/85/21, 25/85/21, and 40/70/21. uF, Hz, and VAC are the same. Could I use these or should I play it safe and make sure everything matches? Thanks!

I'm in Seoul

On 2020-08-21 by Vic

Help needed i have a clarke compressor model se7ar kw 1.1 hp 1.5 volts 240 amp 8.9 rpm 1440 hz 50 can someone please tell me what capacitor i need

On 2020-08-19 - by (mod) - general capacitor recommendations for a 1/2 hp 120VAC Electric motor

Sure, IH, just check out the general recommendations for a 1/2 hp 120VAC Electric motor in the tables above on this page.

On 2020-08-19 by IH

I have DeWalt radial arm saw manufactured in the later stages of WWII. I’m fairly certain it needs a new start capacitor (looks original) but there are no markings on it at all and I don’t know what to replace it with.

The motor’s data plate gives me this information: 1/2 hp, 7.2 amp, 115 v, 60 cy. Can anyone help?

On 2020-08-12 by Mike W

Replaced my 1/2 hp 115V blower motor. Bought the recommended 10mfd run cap. Plugged it all together, motor starts briefly and stops after 1-2 sec. Reused the prior 7.5mfd cap and everything is working great.

Tested the 10mfd cap and it reads good. Am I going to get into trouble leaving the 7.5 in place? Why wouldn't the 10 work just as well as the 7.5? I'm stumped.

On 2020-07-04 by AnnA SerViCeS

1.5 mOtOr capasitOrs details please One capasitOr is 20 MFD and Other One details

On 2020-06-24 - by (mod) - allowed to exceed the capacitor rating by about 10%

Robert

You're pushing limits a little bit. Most sources tell us that we are allowed to exceed the capacitor rating by about 10%

On 2020-06-24 by Robert Gosman

1.1 hp air compressor. I am using 2kw inverter, off grid. Starting current draw 30a (3600w) , my peak is 3500w. Compressor has 60uf capacitor. Can I use 70uf capacitor to close gap?

On 2020-06-19 - by (mod) - how can you tell if its a RUN cap or Start CAP??

Run

By the capacitor size rating in farads or microfarads. The start cap will always be the larger of the two. It takes more of a kick to get a motor spinning than to keep it spinning. You'll see those differences quantitatively in the data given in the article above.

Thanks for asking.

On 2020-06-19 by Run vs Start Caps

When you go to order a replacement capacitor for a motor how can you tell if its a RUN cap or Start CAP??
My pump has a 40 uf cap it comes in BOTH run or Start
Thanks

On 2020-06-17 - by (mod) - Estimated Small Motor Capacitor "Ballpark" Sizes Based on Motor Type

Renjith

See the values in the table

Estimated Small Motor Capacitor "Ballpark" Sizes Based on Motor Type

On this page

On 2020-06-11 by Renjith

Sir


3 phAse 20 hp motor which capacitor required

On 2020-06-06 - by (mod) - guidelines about substituting capacitors and how much variation from spec is acceptable

That should be Ok,

The article above on this page gives some guidelines about substituting capacitors and how much variation from spec is acceptable

On 2020-06-06 by Octavio

Can I use a 440v 40uf instead of 440v 35uf

On 2020-06-06 - by (mod) - check the tool owner's manual for capacitor or wiring diagram

Jan

The best procedure would be to find the owners manual for your saw and find the wiring diagram in the specifications for the actual start and run capacitors that that motor used. You can't find that information you can get in the right ballpark using the table provided above on this page, by noting your Motors horsepower and voltage.

On 2020-06-03 - by (mod) - find A 15 MFD 330 VAC capacitor

William

A 15 MFD 330 VAC capacitor ought to be available at local electrical suppliers if there's one near you, else from an online vendor. Dayton certainly makes several that ought to be in a suitable range as does Titan and as does the original manufacturer of your capacitor - it's probably not quite what you wrote but rather, Aerovox (that's a V not an N)

Keep in mind that you'll be ok with a cap whose voltage is rated higher than 330, but not one whose voltage is rated lower.

Below I'll show an example of a cap that would be fine, easily found for sale online at vendors like https://www.grainger.com/ -in this case a Titan Pro round motor run capacitor rated at 15uF and 370-440VAC.

You can of course also give Grainger a call
1-800-GRAINGER
(1-800-472-4643)

Or contact Aerovox at
http://www.cd-aero.com/
Sales at
CD Aero, LLC
167 John Vertente Blvd.
New Bedford, MA 02745
Tel: 508-910-3500
Fax: 508-995-3000

In case I failed to make this more clear, InspectApedia.com (this website) does not sell anything.
In order to absolutely assure our readers that we write and report without bias we do not sell any products nor do we have any business or financial relationships that could create such conflicts of interest.

On 2020-06-03 by William Vischer

I have and old 1960s Century Capacitor Single Phase 7.5 HP, 230 volt, 40Amp, 1750 RPM motor on an existing grain elevator leg that burned one of the 9 Capacitors out. The Capacitor Motor Control Unit is separate from the motor. Currently running on 8 capacitors hooked in parallel.

Motor still runs fine but would like to find a replacement capacitor which is a 15 MFD 330 VAC capacitor which was part of the cluster of 9. Is it possible to find a satisfactory replacement.? I have all the ID data on the capacitor which is AERONOX RFFU, 170015, 15mfd 330VAC, 132.

On 2020-06-02 by Jan

I was given an old Rockwell table saw. The motor included is 1/2hp 110v 1725rpm 8.0amps. 1 phase.60 cycles, cont.rating.,type S-2872, code 6512, Model GMD-M56B-HSF-BG/575M.(n0 capacitor). I suspect it is not the right motor. Motor hums on start,and will go only if I spin the pulley

.(not a safe situation) Motor runs in 2 directions; depending how I spin the pulley. my question- can an external capacitor be added into the circuitry to make the motor start and run with no help from me.Thanks Jan

On 2020-05-31 - by (mod) -

Do all electric motors need a capacitor to start and/or run?

Frederick,

Thanks for a helpful question: Do all electric motors need a capacitor to start and/or run?

Answer: no, not all. Here are the details:

Pretty much ALL modern single phase electric motors use a START capacitor, either internal or external, to get the motor spinning.

SOME electric motors are designed to run without a run capacitor.

For example, Shaded Pole type electric motors, also known as "single phase induction motors" uses an external capacitor to get the motor started but then the motor can continue to run without a run capacitor. "The four basic types are split phase, capacitor start, permanent split capacitor, and capacitor start/capacitor run." - detail courtesy of Bay Motor Products cited below.

Original AC Motors, going back to Nicholas Tesla's original design, ran without using a start or run capacitor, using instead two windings; the start winding or auxiliary winding got the motor going.

ALL modern single phase electric motors use a START capacitor, either internal or external, to get the motor spinning.

SOME electric motors are designed to run without a run capacitor.

For example, Shaded Pole type electric motors, also known as "single phase induction motors" uses an external capacitor to get the motor started but then the motor can continue to run without a run capacitor. "The four basic types are split phase, capacitor start, permanent split capacitor, and capacitor start/capacitor run." - detail courtesy of Bay Motor Products cited below.

For some of these details we thank Bay Motor Products, "Types of [Electric] Motors: P.O. Box 982, 3100 Cass Rd., Traverse City, MI 49684 USA Website: www.baymotorproducts.com/type-of-motors/ Tel: 231-941-0411 Email: customerservice@baymotorproducts.com

On 2020-05-31 by Frederick - Can a motor run without a capacitor

Can a motor run without a capacitor

On 2020-05-28 - by (mod) - Can you use a 60uf or 70uf to replace a 65uf capacitor?

Robert

70 uf is probably ok

60 uf is probably not

Typically we can use a capacitor that is close to the value of the original one as long as its voltage rating is not exceeded.

From the article above on this page we have this warning

Watch out: When you are replacing an electric motor capacitor, never put in a lower rated capacitor. If you cannot get an exact size match to the original motor capacitor, it is acceptable to use a capacitor rated one step higher in µF. The substitute capacitor must be able to handle the voltage.

On 2020-05-28 by Robert

Can you use a 60uf or 70uf to replace a 65uf capacitor?

On 2020-05-31 by (mod) -

Alama

Those are probably all acceptable microfarad ranges for which the capacitor can be used.

On 2020-05-28 by alama

my ac fan motor dual capacitor oval 3 terminals burn out with mouse dameged can not find uf but i have manual but 3 different numbers 25 7.5uf 35 7.5uf 40 7.5uf but i dont know can you tell me what will i do thamnk you alama

On 2020-05-03 - by (mod) - Why is the rating of run capacitor smaller than start type capacitors?

Shree

Thank you for helpful question.

It takes a much bigger kick or jolt of current to start a motor spinning from being idle than it does to help keep the motor spinning once it is started.

That's why the start capacitor always will have a much higher capacity rating in microfarads then the run capacitor.

On 2020-05-03 by Shreeyash

Why is the rating of run capacitor smaller than start type capacitors?

On 2020-04-08 - by (mod) - motor specifications let us calculate a reasonable start or run capacitor size

The Owner's manual for this Central Machinery disc & belt sander (if you don't have it) is at

CENTRAL MACHINERY DISC & BELT SANDER MANUAL [PDF] from Harbor Freight
There we find the sander's electrical rating as

120 VAC / 60 Hz / 3.5 A

So we know it's a 3.5A motor.

That's about a 0.5 or 1/2hp motor at most.

Armed with that data take a look in the tables above on this page and you can find a reasonable start and run capacitor size.

of about

1/2 Hp or 0.37 KW, 120-150 VAC 320-400 µF - Start Cap 10 µF 370VAC - Run Cap

let me know what you think

On 2020-04-08 by John

Yeah well, the only marking on this hosing is a ground symbol. This thing probably has maybe a 1/4 hp motor.
Pulled it apart to the windings, no data anywhere.

Checked the owner manual specs and the only thing they
note is the rpm speed of the disk, 1819RPM. I’ll try calling HF in the AM and see if their support staff has any
motor data.

On 2020-04-08 - by (mod) - check motor specs to select proper start or run capacitor

John

Let's try to do this accurately: what are all of the data you find on the belt sander motor? Perhaps attach a photo of the sander motor's data tag.

Also check that the motor isn't being bound by some other mechanical fault

On 2020-04-08 by johng - need capacitor for Harbor Freight table top belt sander - Central Machine

I bought a Harbor Freight table top belt sander. A common complaint is slow startup, usually needing a “push” to get it up to speed.

I believe the cap is underrated and should probably be around 100uf.
What are your thoughts? This is the original.

On 2020-03-01 - by (mod) - What are the risks of using an over-sized capacitor or under-sized capacitor?

Thanks for an important question, Dave:

What are the risks of using an over-sized capacitor or under-sized capacitor?

A start cap that is over sized in voltage generally won't harm the motor.
A run cap that is too bit or too small can cause improper, inefficient motor operation and can ultimately shorten the motor life.

From the article above on this page we have:

...

The voltage rating of a capacitor indicates the highest nominal voltage at which it is designed to operate.

Use of a capacitor at voltages below its rating will do no harm.

For example, if your motor used a 370VAC rated capacitor you can replace it with a 370 or a 440VAC capacitor. The 440VAC capacitor will last longer. But because these voltage ratings are simply the peak voltage that the capacitor can handle, using a higher-rated cap (440) where a lower-rated one (370) was originally installed, is not harmful.

Run capacitors must not be subject to voltages exceeding 10 percent of the nominal rating, and start capacitors must not be subjected to voltages exceeding 30 percent of the nominal rating.

...

Particularly for the run capacitor the effects of a cap that's too far off spec for what the motor requires risks damage to the motor as well as improper operation.

The motor's rotational torque may be reduced, and depending on the motor's actual physical load, its speed could be affected, stressing the motor, increasing its noise level, increasing its operating temperature, even causing overheating or bearing failure. You may also increase the motor's operating cost by reducing its efficiency.

A mis-matched run capacitor can throw off the phase shift or phase angle (I'm speaking a bit past the edge of my technical expertise here) between current (amps) and voltage - a cause of the failures listed above.

On 2020-03-01 by Dave

Hello, the Rheem (Ruud achiever series mdl#: RRMA-A042JK10E) AC unit I have has dual capacitor setup. one is a 10uf 370v and the other one is a 55+3 370v capacitor. I am unsure about this second one.

What is the risk of getting a 55+4 or 55+5 instead of the 55+3?
What does this second value +# affect on the HVAC unit?

A local technician told me it didn't matter as long as it was a higher value, but searching online I read differently; however, I cannot find an actual reason why or what actual problem will occur when exceeding this value.

Thank you

On 2020-02-06 - by (mod) -

Glen in the article above on this page CHOOSE a START / RUN CAPACITOR, HOW TO

a best answer is at the section titled

Capacitor Voltage Rating Selection Limits

Please take a look and don't hesitate to ask follow-up questions

On 2020-02-06 by glen

can i replace 55uF+5 start capacitor instead of 45uF+5 capacitor

On 2020-01-08 by Che Kuan Yau - advice for choosing a running capacitor

I am referring to type a) the "motor running capacitor " which is permanently connected in the circuit during running, such as used in the table fan etc., type b) the " motor starting capacitor" which are connected only briefly during starting but switched off by centrifugal switch etc during running;

such as used in the single-phase motor for starting purposes and type c) " power-factor correction capacitor" which are used in single-phase or three-phase pf correction purposes.

I am aware that in most cases the capacity (uf) of a)<b)<c) . they may be of similar rated voltage vac.
my questions are :

1. how to differentiate between type a), b) and c) as they any be in metallic or plastic can or in plastic cube ?

2. whether are they interchangeable, e.g b) replacing a) or c) replacing b) if they are of the same capacity and voltage rating?

3. if b) shall not be used for a) application, why there is no warning of the prohibition on the rating marking?

4. which iec/ansi standards explicitly state their differences and that there are not inter-changeable?

che kuan yau (singapore)

On 2020-01-06 12:57:18.026208 by Anonymous

1.5 hp motor with start capacitor capacity

On 2019-10-14 - by (mod) - I cannot determine the rating of the old capacitor: how do I select a new one?

Take a look at the data tag on the motor or find the IO manual for it as those will often specify the exact capacitor needed;

If you can't get that data then you're left with choosing a cap based on the motor's wattage or horsepower, for which we give some example tables above; your local electrical supplier can take it from there. You may need something like the 10,000 uF starting cap shown here from Walfront

You can calculate the kVAR for a motor then convert that to typical capacitor rating in microfarads or uF

kVAR = motor voltage x amps rating (running amps), e.g.

A 2200W motor running single phase 240VAC = draws about 9 Amps.

9A x 240V = 2160 kVA

https://www.electricaltechnology.org/2013/11/how-to-calculate-required-capacitor.html

gives

Required Capacity of Capacitor in Farads/Microfarads

C = kVAR / (2 π f V2) in microfarad

for which example calculation details are given at that site; however it'd be safe to stop by your electrical supplier with your motor specs. Below: example of motor capacitors from Rubycon.

On 2019-10-13 by Chris

I have a 30 yr old thicknesser which uses a Leroy somer 240v single phase 2200w motor. Unfortunately the start capacitor has failed and I cannot determine its rating. Is there anyway to find out.

 

On 2020-11-29 - by (mod) - how to test an electric motor capacitor

Patrick

First apologies: the stupid Comment Box profanity filter thinks you should not type the word S C R A P I N G and they change some of those letters to L O V E - I've complained but they're focused on "higher priorities" for the moment. You're among the few who figured out hot to get past it. For a while I thought our readers were teaching me a new word "slovee" for "s c r a p e " .

When the motor won't start, is getting the right voltage, is properly-wired, and disconnected the motor spins and the bearings are neither jamming nor so worn that maybe at start-up the rotating parts jam, we naturally suspect a bad start capacitor.

Watch out: you can try checking voltage in to a cap and even the much higher voltage out using a DMM or VOM, but if you slip up you can get shocked or killed.

Take a look at TEST a MOTOR START or RUN CAPACITOR

And let me know what you find.

On 2020-11-29 by Patrick

Looks like my previous message did not get saved ...

So I disassembled the motor of the wet grinder completely today.

Motor was very clean inside, no debris. Stator, rotor appear fine. I did notice some very minor sc r-aping on 2 of the windings but I do not think this could cause a problem (I'm no expert though). The bearings were fine - some dust on the bottom one but nothing unexpected, both run smoothly with no resistance or clicks.

I also removed all the sleeves containing the wiring to inspect the wires and all looked fine.

Current situation is the same: motor does not start by itself (and hums), but does go with a small push, and seems to run OK afterwards (I have not checked amps or watts today though).

I think I need to check that there is current going in and out of the capacitors.

How would you proceed to do this? Would you do this "live" or with the machine turned off?

Thanks for your help, I'm learning a ton these days!

On 2020-11-29 by Patrick

S-c-r-a--p-i-n-g!

Today I completely disassembled the wet grinder motor. Very clean inside the stator, no debris or dust, very clean rotor, bearing are fine (some dust on the bottom one but nothing unexpected) running smoothly.

The windings look good too, though I did notice some very light Lovering on two of them. I would not think that they are problematic, but I'm no expert.

I also removed a couple of sleeves containing some of the wiring (especially the ones to the capacitor) and they look fine.

The current situation is the same: motor does not start by itself (and hums), but does go with a little push and seems to go well, though I haven't checked power or amperage today.

I think I need to test some connections with a multimeter (and maybe capacitance meter?). I'm not completely sure how the capacitor is fed current and feeds it back to the motor ... How would you proceed to check that the capacitor is fed current (would you test "live") and that it does feed back to the motor?

Many thanks for your help, I'm learning a lot these days!

On 2020-11-28 - by (mod) - Hitachi EC89 air compressor trips circuit breaker

Richard

If you know how to do so safely, checking the actual current draw using an ammeter or digital multimeter that can measure amps would be very diagnostic.

It's quite possible that the current draw is high enough that even changing to a bigger breaker wouldn't prevent the breaker from tripping.

And I'm sure you realize that going to a larger breaker risks of fire so your experiment was interesting but not one that I would repeat

On 2020-11-28 by Richard Dicker son

one of my lawn mower customers wants me to look at a Hitachi EC89 air compressor.

It starts right up but after it runs long enough to pump up to about 50 lbs it trips the 12 amp circuit breaker. just for grins I connected an auto style 20 amp fuse in place of the breaker thinking it was a bad breaker.

Still blew that in the same amount of time. since it starts right up I'm ruling out the capacitor. Just looking at the windings looks good. which wires coming out of the motor do I need to probe to check for shorts and what should I expect to see?

I a blurb someplace that a leaky valve in the pump can cause this is this right? Just feeling around on the motor and pump housings it doesn't feel very hot any place.
Any help is appreciated.

On 2020-11-25 - by (mod) -

Got it,

Thank you for clarifying and explaining it to me. You might want to check the motor bearings

On 2020-11-24 by Patrick

The replacement capacitor I used is a spare from the manufacturer. I also literally took out a capacitor from an identical machine which runs perfectly.
The coils look OK but perhaps there is something's inside the windings or rotor that I'm not seeing.

Do you believe that something inside the motor could cause a loss of power?
I think chocolate is not conductive at all but I imagine it could interfere with the function of the motor.


PS: its a 240v 6 pole induction AC motor,it runs around 150W with a standard load but can go up to 180W

On 2020-11-24 - by (mod) -

Patrick

Your diagnosis sounds reasonable; but maybe you're not using the right starting capacitor. Check the motor's data tag.

see also CAPACITOR SIZE DETERMINATION for ELECTRIC MOTORS

On 2020-11-24 by Patrick

My wet grinder was running slow today so I opened the casing and found that some product (liquid chocolate) overflowed and made it inside the casing - gears/cogs and belts were affected but nothing got inside the stator/rotor or the motor pulley.

Upon cleaning everything I tried to start the motor but it wouldn't start by itself (but it does run if I rotate the pulley a bit). I swapped the capacitor (8uf, and also tried 10uf) but got the same issue - it acts as if no capacitor is connected - and also shows a loss of power (100W versus 150W normally).

The wiring between motor and capacitor appears fine, and the motor shaft rotates freely with no resistance.

I'm a bit perplexed ... the capacitor is probably not the culprit, I can't find any obvious issue with the wiring, and the motor does run, albeit slowly....

Where would you look next?

On 2020-10-23 - by (mod) -

Joseph

Probably the motor has a seized bearing

On 2020-10-22 Joseph withal

I have a capacitor run motor which blow the capacitor it is a baker fan for cooling the cool after replacing with same rating motor did not function no humming sound what could be the problem help.

On 2020-07-23 by Anonymous

The motor was missed wired to have a high HP (has two separate wires for 1/5 to 1/4 HP (red) and 1/3 to 1/2 HP (black) It was wired for the 1/3 to 1/2 HP. I rewired the motor to have higher resistance on the Lines (Red and White connected to the lines).

The voltage to the capacitor dropped to normal 303 VAC at the capacitor. The over voltage has likely damaged the capacitor that reads 303V with 1.04A that give 9 MFD instead of 10 MFD. A Back EMF from the motor.

Strange that the compressor's running capacitor's voltage has also dropped from 419 VAC (a few days ago to 357-391 VAC today.

On 2020-07-22 - by (mod) -

Dave

Please help me out if I'm missing something button or if I misunderstood, but the capacitor doesn't affect the incoming voltage.

That would be a problem from your power source.

On 2020-07-22 by dave

The run 10 MFD capacitor was shorted for at least a day to a Top Tech TT-C50-MSP2 multiple HP fan motor (5 years old replacement motor and fan). The new capacitor was tested before installation and while running. 10 MFD before and 8 MFD while running.

The voltage is high 460 VAC and 1.38 Amp at the capacitor 8 = 1.38 * 2652/ 460 V .

How to fix that the voltage is too high? The current at the fan leads are 1.4 amp and 230 VAC.

The plate on the unit has a 1/4 HP fan motor and information sheets on the inside 1/5 HP motor.

On 2020-06-06 - by (mod) -

Sounds like a bad cap, wrong capacitor, or wiring error,
or
more-likely, a pump with a bad bearing that's shot.

On 2020-06-04 by Char mon

installed new start capacitor on my table saw. Motor was just humming to begin with. After installing the new one, it will turn for a few seconds (If I give it a spin first). But after a few seconds it trips my breaker. Any ideas?

On 2020-04-04 - by (mod) -

Thanks for the interesting question, John: Why might a motor not start when warm?

It could be a capacitor that fails when hot - sometimes heat can cause slight movement in electrical components that opens up an electrical connection or causes a change in operating properties of a capacitor.

But also possible is a motor that is overheating, either tripping off on thermal reset (some motors will automatically reset when they cool down), or a hot motor can suffer from a tight or failing bearing so that it trips off on startup when hot.

Some motor testing and an new start/run cap are in order.

On 2020-04-04 by john

I know the capacitor is not 100% but why will it start an oil burner motor when cold but goes to lockout when warm.

On 2020-03-20 - by (mod) -

Fred:

All new parts and a motor that won't run suggest
- mis-wiring
- a bad control board or relay

On 2020-03-15 by Fred Johnson

New 220v a/c motor for air compressor will not run. 125v to each hot lead at the motor

On 2020-01-14 - by (mod) -

Peter


Please find your question and our very detailed reply now found at

CHATTERING WATER PRESSURE CONTROL SWITCH

On 2020-01-13 by peter

The 3/4hp electric motor on my residential water pump initially cycles on/off several times before remaining on until the correct shut-off pressure is reached. Then it does the same thing before shutting off. I've replaced the pressure switch on the pump but the problem persists. Why?

On 2019-10-10 - by (mod) -

When the two wires are the same color I expect the manufacturer intended to say that it didn't matter which went to which terminal.

On 2019-10-09 by howard

The connector on my whirlpool washer cap broke off. It only has two red wires to it. Does it matter which wire goes to which connector

On 2019-09-15 by (mod) - I have to spin the motor to get it to run

Audi

Please see CAUSES of HARD STARTING ELECTRIC MOTORS

On 2019-09-15 by audibontiri

I have a spin motor used in a clothes spinner. Motor hwve no enough torque to start but has installed capacitor at rated capacity. What could be the problem?

On 2019-07-15 by (mod) - cause of burned relay: hard starting motor?

A burned relay could be caused by a motor that is beginning to seize and is drawing High current - that would be measured in amps when a circuit is trying to run the motor, not volts.

On 2019-07-14 by Anonymous

just pulled the relay and it's clearly burnt as well. Just can't diagnose where the extra voltage would be coming from. condenser or motor..

On 2019-07-14 by Brian

This is similar to a problem I'm working on right now. I replaced a bad motor run cap ( motor would run is i gave is a push but would not start on it's own)

I finally replaced the cap and about a month later I came home (to a boat, roof top ac unit) Teh white wire coming from motor to cap was burnt. I replaced the wire but the breaker still trips after about 20-30 seconds. The cap is good, holding a charge, at least 12v, which is what i tested it with). thoughts?

On 2019-07-14 by (mod) - underlying problem: failing electric motor

Mac,

Sometimes when we replace a capacitor to get a motor running again we are not addressing an under cause such as a motor which is itself actually failing. The motor could have a bad bearing for example.

Therefore at this point it would be appropriate to check all of the leads and connectors to the motor and the capacitor, and if those are intact, check for a bad fan relay and if that appears to be working then it's time to pull the motor and do some diagnostic tests on the motor itself.

On 2019-07-14 y Mack1441

I had my capacitor replaced and that seemed to solve my issue (fan was not turning). Unit came on fan was working and it seemed to be cooling down the house.

A few hours later, I noticed the temperature in the house was rising again. Checked fan outside, it was not turning again. What could have gone wrong now?

On 2019-05-23 by (mod) -

Is there not a run capacitor? That may be bad.

Or there may be a bad centrifugal switch that isn't cutting out the starting cap.

I'd look at the run cap before blaming the winding.

On 2019-05-23 by Elbass7

My single phase 0.75 switchless motor is made to run on 240 vac. It starts, but doesn't run.

After applying power it soins up to about 1000 tpms and then starts slowing down, then the temp protection drops out. I measured the amps at starting with no load and it begins at about 29 amps and drops to 24 just before the protection kicks in. It has a start capacitor that I replaced.

Is it the run winding? I measured about 3.4 ohms on the power terminals and 1.2 at the cap connections. Any guidance would be appreciated. Elbass7

On 2018-12-27 by (mod) -

Walter


Thanks for an interesting question. Age per-se isn't an issue but if a capacitor is actually failing then yes it can affect a motor's ability to start or its ability to keep running smoothly.

On 2018-12-26 by walter

as a run capacitor ages does it affect the motor rpm

On 2018-12-12 by (mod) -

Electric motors that use a start capacitor typically have a centrifugal switch inside the motor that opens when the motor gets up to speed. That may be a broken part in your motor.

On 2018-12-12 by Johan

My submersible well pump starting capacitoR does not switch off, then overheats. What could be the cause?

Question: the capacitor is leaking oil

(June 15, 2015) Larry said:

I noticed my air conditioner's run capacitor is leaking oil - what does this mean?

Reply:

The capacitor is shot and should be replaced.

Reader Question: replaced both start & run capacitors on AC compressor but compressor won't turn on

(June 15, 2015) Larry said:

Trane Xl1600 heat pump cools down to set thermostat setting and then will not turn compressor back on and blow hot air in the home.

This seams to happen when Phoenix temperatures reach 100 degrees. Replaced both start and run capacitors a couple months ago as issue started last summer was working fine until 100 degrees. Any assistance with this would be greatly appreciated.

This question was posted originally

at DIAGNOSTIC GUIDE A/C or HEAT PUMP

Reply:

Larry if replacing the start/run caps didn't fix the trouble I suspect either a failing control board / relay or a compressor motor that is failing beyond the ability of the starting cap to kick it off. Perhaps your tech will check the current draw of the various motors involved to see if that's going on.

Question: possible to rebuild 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.

Question: clarifying dual start-run capacitor nomenclature

(June 16, 2014) Danno said:
I'm replacing the capacitor in my AC condenser. The original/stock unit says 35/5 440 AC. This is the cap I ordered from a distributor, but upon receiving it, the box says "5/35 440" (the 5 and 35 are transposed. Distributor says its the same thing. Is this correct? Thanks for any 411

(June 18, 2014) Mark said:
I always was taught that 35/5 was a run capacitor. 35 is the microfarad rating for the compressor & 5 microfarad was for the fan. (three terminals) not:

Decode a 35/5/440 marking on a motor starting capacitor

The capacitor you are describing marked 35/5 440 is probably a dual start & run capacitor.

35/5 : The first two numbers are the capacitance 35 uF (start) and 5 uF (run).
440 refers to the ability to run voltages up to 440VAC

(Aug 30, 2014) Bob said:
I was told my A/C unit has two capacitors. The unit stopped running, no fan at all, I located the dual capacitor and it checks out fine, so where is the second capacitor?

Does Lennox use a dual and a single capacitor

(Aug 30, 2014) Anonymous said:
I have located the dual capacitor, what would the second capacitor look like

Reply:

Thanks Mark, I've included your helpful explanation in the article above.

Anon, thank you for griping about the difference between start and run capacitors. I'll review the text above for clarity and edit as needed.

Run caps are sold as single capacitor (two terminals) for a single purpose (keep the motor running) and rating (rated in mfd or uf) for the motor (such as 45uf for a compressor or 5 uf for a fan motor)

Dual run caps combine two capacitors in a single unit, one for compressor and one for fan, such as a 45/5 MFD unit, and will have 3 terminals as detailed in the text above (compressor, fan and common)

Start caps have the single job of getting a compressor motor spinning and of course are rated at a much higher MFD number. Mark summed it up nicely below and again in the article text above.

Bob if your unit has a start-run capacitor, a dual capacitor, that unit may be the only one present.

Capacitors may be found for the compressor/condenser motor and separately for the fan motor (on some units) - follow the power terminals of the equipment back to their power source.

The capacitors used on your particular Lennox unit will be described in the installation, maintenance and wiring manual or obtained by giving Lennox a call with your product model number.

Question: Marine AC compressor shuts down

(Sept 16, 2014) Ira said:
This is a question regarding a marine a/c unit, but is virtually the same as any other unit.

The problem is that when I initially start the unit in the morning it will run for about 30 seconds and then the compressor shuts down, but the fan remains on. I shut the unitI wait a minute and turn it back on and it then runs perfectly all day, wether I leave it on to recycle or turn it on and off manually.

Reply:

Ira:

has anyone checked for a failing start relay?

Question: clicking noise in Goodman Heat Pump

(Oct 6, 2014) Diane said:

I hope someone can help me fix my goodman 3 ton heat and air unit heat pump.

The trouble I'm having is I heard this clicking noise like the fan trying to come on, but never did until

I took a stick and pushed the blades and they started moving than I went inside the house and the air coming out was not cool could anyone tell me where to start checking, I,m going to try to fix this myself .

(Nov 20, 2014) Daniel said:

I woke up this morning, the ac unit was on the fan was working but there was no air coming from the vents inside the house, I went outside to see what I could do everything seem to be working but I think the condenser motor it was humming. and real hot to the touch. can someone give advice on what it could be?

Reply:

Diane

If the indoor air handler unit is running but no air is coming out of the air supply registers I suspect that the blower assembly has failed or duct connections have come loose.

Check first for a blocked air filter or crimped air ducts. Watch out: an air filter that got sucked into the blower assembly can cause a fire.

Question: suspect stuck rotor in Panasonic AC Compressor

(May 6, 2015) Mohiddin said:
Sir, this is about Panasonic 1.5 ton AC compressor. The compressor ceases to start, tried with replacing the 45Mfd/440V capacitor with new one. Still the comp ceases to run and getting heated up. Checked the winding continuity and found to be OK.

Suspecting the rotor has stuck. can I try to run the comp in reverse to release the stuck rotor or can i increase the starting torque boosting by adding a parallel capacitor to the existing 45Mfd capacitor?

Reply:

You might get such a motor running but I'm doubtful it has a useful remaining life.

Mohiddin

It sounds to me as if you need a new compressor. Even if you got it running by banging it around, its continued service is doubtful.

Question: old AC unit startup trouble

(May 6, 2015) Bruno , (Architect 5512 (RET> ) said:
Unit has been great, for many years

This year ,when I tried to use it, (It didn't seem to,"get to the 2nd step" (See Above ? )
Using ..(my intuition only , I am a "Mustang Architect,and 10 year carpenter tradesman prior)
So Do you think I am on the "right track ??

Thank you for your absolutely great Web-Site Bruno

Reply:

Sorry Bruno I don't understand the question

Question: how much to replace a compressor or motor

(June 10, 2015) Anonymous said:
Diagnosis

1. the compressor needs replacing

2. motor needs replacing

How much should each cost

(July 19, 2015) John said:
Blower motor inside tries to start but acts like power is being interupted. Starts and stops erraticly. This happens in "fan only" mode also.

(Aug 17, 2015) Paul said:
Need to start fan blade with a stick to get it started, run for awhile then stops. Is it a capacitor issue. Feel the copper lines running into the house just slightly cool. Should they be ice cold?

Reply:

Paul, that's probably a bad capacitor

Question: Value of the start run capacitor for refrigeration

(Sept 27, 2015) Anonymous said:
the value of the start and run capacitor for refrigeration

Reply:

It depends on the voltage requirements and ampacity of the motor it's starting or running; see the motor data tag.

Question: will a capacitor help my old Maytag washer motor?

2015/11/26 espo5646@hotmail.com said:
I would like to know if a capacitor would help start my old Maytag washer motor. It has a centrifugal switch that opens as the motor starts.

The motor will run if I turn it by hand and continue to run. The motor is welded so I can not open the housing.

It has six wires coming out of the motor which is a two speed Model LR22286 1/3 HP, 1725 /1140 RPM Code R. I don't know that much about electric motor types, but thought that if the start winding is bad, a capacitor might help. Thank you

Reply:

Espo

If your motor already used a start/run capacitor, now won't start, and will run if given a spin, then yes replace the capacitor with one of same values.

A bad winding, however, won't be fixed by adding a capacitor.

Question: where is the start capacitor located on a Carrier Model 38YCB024 310

(Jan 23, 2016) (mod) said:
Curls said:
Can you tell me where physically the start capacitor is on a Carrier Model 38YCB024 310? Here's the wiring diagram ,,,

My fan wasn't working and after learning, I replaced the dual run cylinder capacitor in the side box on the outside unit. Now the fan is working again.

I see in the wiring diagram a start capacitor, and I've found one for sale that cylindrical. Yet I don't see it in the box. Since the other two were five years old and bad, and this one was never replaced on this 20 year old system, I'd like to know where it is and be prepared.

Am I haven't a moment like when you're looking at grocery shelves and can't find the item right in front of you? Or is it somewhere I'm not thinking of. Thank you so much. I've searched online but haven't see it yet.

Reply:

Unfortunately, Curls, a wiring diagram is a logical presentation not one that shows you where the physical components are located. Look at the appliance and its controls and wiring and you should be able to recognize the actual physical capacitor. Also some installation manuals include, in addition to wiring diagrams, photos of controls and control boards that can help;

WATCH OUT for death by electrocution; properly this repair is performed by a trained service tech.

See LOCATE the STARTING CAPACITOR

(Jan 24, 2016) Curls said:
Thanks

I was hoping someone could tell me physcial places to look where it might be. The only place I know to look is the side panel of the outside box. Is this compressor start capacitor sometimes found somewhere else?

Where might that be (inside where the fan is? Inside the inside-the-house air handler?). I can't imagine where it is, and don't want to open them up if it's not possible to be in those places.

While it's on the schematic, do some units get built without this capacitor even though on the general schematic (in other words, do they make a series of models where this factor might differ?) Thanks again!

I replaced the capacitor after turning off electricity at the fuse, testing, and discharging the capacitor with a screwdriver against the terminals. I'm curious why my question drew a safety warning when practically none of the other questions did. What amount mine made me look more prone to taking risks?

Moderator reply:

Curtis:

there may be start capacitors, combined start/run capacitors, or pairs of caps at the compressor/condenser unit (outside) and also inside the air handler at or near the blower fan or fan motor.

You won't see these devices without opening the service covers to the equipment - watch out for death by electrical shock or cut fingers by moving parts.

Often I see a pair of caps jammed in up under the cover of the compressor/condenser and a cap at the blower motor assembly.

Question: electric motor for pool pump not working: subject to Houston TX Flooding

(Apr 18, 2016) john said:
have a pool pump motor--it starts real hard-sometimes I do not think it is going to start-so far it has--it is a little noisy when it runs--new start cap new run cap new bearings new impeller--everything is new---any ideas
thank you
john

Reply:

John, with the motor disconnected, can you spin the shaft by hand? Does the impeller also spin freely?

Other things to look at besides bad bearings and starter cap are discussed at ELECTRIC MOTOR DIAGNOSIS (search for that article in the box above).

I'd probably start by checking
- all wiring connections
- voltage being delivered
- current draw at startup

(Apr 19, 2016) Anonymous said:
volt ok
wiring ok

imp spins freely

we are having bad weather here in Houston--I will ck the cap when weather breaks
it is running it just starts hard---think it's the start cap
john

Reply:

Indeed Houston is suffering significant flood damage and of course 17+ inches of rain mean high humidity that in turn can cause trouble in electrical components that are already marginal or are not protected from water. Replacing the capacitor is easy and inexpensive. Try it. Keep me posted.

(Apr 22, 2016) john said:

got the cap--it is a 189/227 mfd & it reads 194mfd--but I think there is a prob,this cap is 110v--the pump is 220v should the cap be 220v

MOderator reply:

I think so, John. I'd worry that it won't have enough kick or that it will fail.

(Apr 22, 2016) Anonymous said:
I think that is why it is hitting so hard/to long to start----if it should be a 220v cap what size do I get? if the 110v is 189/227---should the 220v be 95/113---how do you figure the size of cap you need?

(Apr 25, 2016) john said:
if I need a 220v cap instead of a 110v----what size 220v cap do I get----the 110v cap 189/227 should the 220v be 95/115

Question: exhaust fan not moving when motor is powered

(May 12, 2016) raju said:
my exhaust fan not moving when give supply to motor. and without supply moving freely.

Reply:

So I suspect, Raju, a bad motor or a bad start-run capacitor.

Other readers; I'm reluctant to pretend to specify specific start/run capacitors based on simple e-text queries.

Take a look at the specs on the capacitor you're replacing, or take a look at the motor data plate specifications; take that data to your electrical supplier.

Typically you'll choose from a limited range of general purpose capacitors that cover the operating range of your motor's voltage, current draw to start (LRA) and run (RLA).

Question: Bryant AC keeps blowing the start capacitor

2016/06/01 Jerry said:
Bryant AC keeps blowing Dual SC. Put a new one in, changed contactor, and it runs, however, the cap will fail at least once a year. Any suggestions. BTW, is the relay located on the compressor, like in refrigerator comp?

Reply:

Check the current draw; chances are the motor is seizing. Or there's a short or mis-wiring.

Comment:

RE-posting without disallowed advertising link:

Rob Erto suggested checking U.K. sources for motor capacitors.

Thanks Rob. While we don't permit posting advertisements, we are happy to identify, cite, and link to contributors of technical content or critique of InspectApedia's material.

Question: AC compressor won't start and draws high current

(June 8, 2016) engineer khan said:
my spit Ac compressor just kick to start but failed and also draw very large current from normal when the compressor try to start

Reply:

See BURNED-OUT COMPRESSOR

Question: fan runs slow until you give it a push

July 13, 2016) Fan starts but runs slow till you give it a push? said:
Fan starts but runs slow till you give it a push?

Reply:

Sounds like low voltage or more likely a bad start/run capacitor.

See CAPACITORS for HARD STARTING MOTORS

Question: diode on st9160b is hot to touch and motherboard is discolored brown

(July 17, 2016) Richard said:
White diode on st9160b is hot to touch and motherboard is discolored brown and somehow the wall port shorted out. When unit is on, only green blinking light on the heater comes on, no fans come on. is the problem with the st9160?

Reply:

For other readers, Richard's ST9160B is a Honeywell heating furnace circuit control board. The ST9160AC is an electronic fan timer. Below I'll excerpt from the company's description of this board. So we have a failed control board; unless you're an electrical engineer with training in circuit board design and repair, I'd not attempt to repair the board.

More important is to determine if the failure originated on the board or elsewhere in the appliance. I can't guess that from a one-line e-text.

The ST9160A-C Electronic Fan Timers integrate control of all circulating fan operations in a gas warm air appliance. This control is the central wiring point for most of the electrical components in the furnace. The ST9160 monitors the thermostat for heat, cool, and fan demands and controls a two-speed circulating fan as required.

Communication with the SmartValve™ System Control initiates appliance light off. The ST9160 features a fixed or field-adjustable heat fan on delay and a fixed or fieldadjustable heat fan off delay, depending on model. Cooling fan on and off delay is fixed.

Specific timings vary. See appliance label or instructions for timings that are available for a specific appliance. Refer to Table 1 for model specifications. Electronic air cleaner (EAC) and humidifier (HUM) convenience terminal connections can be provided as an option.

Continuous low speed indoor air circulation is also available as an option. Thermostat connections are screw terminals or quick-connects.

Question: AC has trouble starting when running on a generator

(Aug 3, 2016) Brian said:
I have. Honda 1000w generator.

I bought a small A/C unit. 444 watts 3.8 amps. However very seldom will it get past it startup mode and not trip the factory beaker built into the generator.

If I can get it to start the A/C unit, all is well. Keeps running the A/C all day. So my thought is, can I make a capacitor booster that will get me past the start up surge needed to start the A/C unit ?

Reply:

Yes, I'd see CAPACITORS for HARD STARTING MOTORS and also see MOTOR CAPACITOR TYPES

Question: replaced condenser fan motor & capacitor, now unit won't start

(Aug 3, 2016) Anonymous said:
Replaced condenser fan motor and capacitor now unit won't start but indoor fan will blow. Replaced condenser fan motor with a universal 4 wire motor and old 45/5 capacitor with new 45/5 capacitor and unit will not run at all. Idk what's wrong and can't figure it out it ran fine other than a bad motor now it doesn't do anything.

Reply:

If the motor is tested and runs when out of the equipment but won't run when installed then I suspect a control board or contactor or relay failure.

Question: is it easy to replace the capacitor on an A/C motor? My AC compressor tested at 200 megaohms which the tech said is very low

2016/09/10 johnteh said:
I had the summer A/C inspection done was told the compressor capacitor was indicating a short life because the compressor mega ohms was 200 which is very low for a unit that is only 2 years old. recommendation was to replace compressor capacitor with a hard start to prolong compressor life.

Are compressor capacitors difficult to replace/install? They don't seem to be, since they have only 2 wires.

Reply:

Jon

For a detailed reply to your question please

see BASIC ELECTRICAL TESTS for BURNED OUT COMPRESSOR MOTORS at inspectapedia.com/aircond/AC_Compressor_Burned_Out.php#Basic

On 2012-12-19 by Anonymous

Replace thermostat and capacitor relay too.and the fan is not work

On 2012-10-03 by stevo

the afcap site is no longer on line , but from what I can remember the capacitor values given in their charts are for 50 Hertz applications.

On 2012-08-30 by Michael

This is a great writeup! Very informative and with great pics. If I could pls describe what I'm seeing on my system...

We have what a pretty standard upright AC & blower home system. It is similar to the pics. We have the starter cap with 2 leads, indicating it's a starter cap and not a start-and-run cap.

For about 2 weeks we heard a squeaking / wobbling coming from our air handler, clearly audible throughout the house when it was blowing. If I didn't know better I'd say it was about the sound a failing belt makes, but we have no belts in this.

Tonight, the blower won't start up at all. Compressor outside the house starts fine. I hear and feel coolant moving thru the lines. When the blower tries to start, it makes a loud buzzing sound for 3-5 seconds, then stops. I figure this is the cap trying to start the motor.

During these seconds, I'm getting around 175VAC across the 2 leads of the cap. Tells me it's got voltage coming out. The circuit board transformer indicates 20VAC and it is indeed putting out 20VAC.

I think, based on this, it is the blower motor? We have an HVAC shop nearby that can get me the parts... but should I still try the Cap first (waste $40 if it is the motor) or just go for the motor? Thank you!!

On 2012-08-27 by Jeff

Replaced starter capacitor and burnt again within hours??? pleae help

On 2012-08-26 by Cameron

Mine would either blow a fuse once in a while or not cool (restart right away) if not left OFF for a longer time period. Got a hard start kit, opened the main unit up, existing cap is open and reads about a meg ohm consistantly, doesnt hold any charge (has the date 8-97 written on it).

To my amazement, there is already a older hard start kit installed (been at least 5-6 years since being serviced, but may of been there longer than that). The olde hard start kit was the only cap starting the compressor. I removed the olde hard start kit, put in the new one (has a larger cap).

So far works like a champ, however time will tell (been only a few hours since). If I replace the "open" cap (or the 1 meg resistor as it is now)with one of the same value, Id only be adding 50uf back again. The compressor is as old as the cap (97).

I am tempted to not add back the 50uf as the *new* hard start kit is rated a much more higher mfd rating. If the problem creeps back up, I have several options...

On 2012-08-25 by K

Our York heat pump (20 years old) blew the capacitor which fried the safety switch. Our tech says the switch is too difficult to replace because entire unit has to be taken apart and that we need a new unit. Does this sound right? Thanks

On 2012-08-23 by John

Thanks, anonymous. I opened up the access panel, and the hard-start capacitor had a fried wire. It's a Cera-Mite that's obsolete. I'm going to replace it with a Supco power-pak spp6 that sounds like it will be adequate. I have a new run-start capacitor on order as well, just for good measure. Given the price, I'd rather do them both now than wait for the run-start capacitor to fail (probably next August in the "dog days").

On 2012-08-23 by phil

I have 2 dmqb series acs .Blower motors need a push to get started.I replaced start capcitors and run capacitors on 2 different occasions but problem keeps coming back.Problematic since new .Any help would be appreciated.Thanks.

On 2012-08-16 by Lucien

40 amp ac breaker randomly trips. Sometimes a week or two apart.
Usually late afternoon.
Typically has 25 amp draw.

On 2012-08-13 by (mod) -

Sounds as if it's worth a try

On 2012-08-12 by norm

I have a 4 ton a/c unit for my house, the fan will just hum when the unit is turn on, I will give the fan a push and it starts to work, then the unit freezes up, I have a Payne A/C unit,
I have read a little about the run/boost capacitors, could this solve my problem? my unit is about 4 years old

On 2012-08-12 by steve

service tech says my trane a/c needs a start up kit a/c runs just fine how do I know if it starts slow? a/c is a 2003

On 2012-08-11 by Anonymous

John it sounds as if your compressor is not starting - usually the first thing a tech will try is replacing the start/run capacitor.

On 2012-08-11 by John

Outside condenser unit makes a low volume humming sound for a second or two, then stops. This repeats indefinitely, until the system is shut down at the thermostat. Neither compressor motor or fan running. Could it be the starting capacitor? Thanks.

On 2012-07-21 by (mod) -

Jeane wild guesses include that a power surge can kill a control circuit board or on occasion blow a start run capacitor.

On 2012-07-20 by jeanne

My ac was running fine until we had a few power blinks.. Now the inside blower is working but, the fan outside will not come back on.. I've checked all breakers and turned the breaker off and on just to be sure... Any idea why the fan outside will not come back on??

On 2012-07-20 by (mod) -

Jeremy, probably not. If your thermostat SET temperature is higher than the actual room temperature then the thermostat is NOT calling for cooling and the A/C system should not run.

On 2012-07-16 by frank casupang

thank you this is very helpful and imformative subject.

On 2012-07-16 by Jeremy

If it is normal that the outside central ac unit keep running all the time as soon as we turn the electrical box switch on. In order to stop it I have to turn the electrical box switch off.

On 2012-07-15 by Anonymous

the motor just has a light buzzing noise when turned on. i kicked started the fan blades manually and the motor ran, but a little shaky. everything seemed to be running inside and out but the air was not cold after three to five minutes so i shut it down?

On 2012-07-15 by (mod) -

Jana, you could wire caps in parallel, but if the one you installed is working properly and is the right size for the unit and the motor is still not starting I suspect there may be another problem. Try leaving the equipment off completely for two hours, then turning it back on. If the compressor starts easily then the problem could be difficulty starting against high head pressure.

On 2012-07-15 by (mod) -

Thanks for the nice note Jessica, we work hard to make InspectApedia information accurate and useful, so we are really happy when we hear from a reader that an article is a success. We also welcome questions or content suggestions as it is of benefit to everyone. - Daniel

On 2012-07-15 by Jana

Mine is just 3 years old it has hard start problem i changed the capacitor still same issue can i series tow capacitor?

On 2012-07-07 by Jessica

Thank you for these awesome pages! We were able to replace our capacitor ourselves on our AC unit, saving a bundle! Thanks so much!

On 2012-06-21 by (mod) -

Julian, if when the thermostat calls for cooling the outside compressor/condenser turns on but the indoor blower does not, I suspect a problem with the fan motor, start/run capacitor, or relay or circuit board.

Double-check those thermostat settings to be sure the fan is not set to OFF and check that the blower unit has power. A tripped breaker, an open blower compartment door (safety switch), or a condensate overflow pan switch can all turn off the blower even if otherwise it's in good condition.

On 2012-06-21 by Julian

Hello,my heat pump outside works fine, but the problem it's the inside unit that is located in the attic, blower doesn't turn on.

Outside unit look fine, cooper pipes are very cold and with the time running, some ice star to form. We replaced the motor in the inside unit 14 month ago. Maybe it's a capacitor problem? And the capacitor for the inside unit, it's inside or outside? Thanks in advance.

On 2012-06-20 by (mod) -

Joseph it sounds too dangerous for me to guess without a wiring diagram of the devices involved. But you should be able to check the wiring diagram for the present and the proposed cap - often dual function capacitors are start/run units- see what each wire from the dual cap offers and see if it matches the original system.

On 2012-06-20 by Joseph St.George

I have a 5 UF and a 20 UF capacitor on my A/C unit. I believe the 5 UF is for the fan and the 20 UF is for the compressor. I have a dual capacitor that is 25+5 OUF and I was wondering if I could use this to replace the two old capacitors.

...

Continue reading  at MOTOR CAPACITOR TYPES or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see MOTOR CAPACITOR FAQs-2 - more recent Q&A about troubleshooting or replacing electric motor capacitors

Or see these

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• COMPRESSOR / CONDENSER DIAGNOSTICS
• ELECTRIC MOTOR DIAGNOSTIC GUIDE
• HARD STARTING ELECTRIC MOTOR CAUSES

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