Electric motor test & repair diagnostic FAQs:

Questions and answers about diagnosing and fixing electric motors. The page top photo was taken of of an oil burner electric motor not an air conditioning blower fan motor or pump motor, but you'll see that all of these electric motors look a lot alike.

This article series describes A/C electrical motor troubleshooting: here we provide an electric motor diagnostic table, a troubleshooting guide that helps diagnose and repair most electric motor problems for motors found on HVAC equipment in buildings such as air conditioners, furnace or air handler blower fans, oil burner motors, well pumps, and condensate return pumps.

A/C Electric Motor Troubleshooting FAQs

at left our photo illustrates the motor as typically found in a direct-drive HVAC blower or air handler assembly.

[Click to enlarge any image.]

These questions and answers were posted originally at ELECTRIC MOTOR DIAGNOSTIC GUIDE - topic home. Be sure to check that article.

 

On 2020-11-27 by (mod) - If the air handler blower fan motor is not starting

If the air handler blower fan motor is not starting the problem could be a failed motor, bearing, or simply a bad motor capacitor.

You changed out the run cap but what about the starting capacitor?

On 2020-11-27 by Pamela

Maybe you can give me a little direction....'a/c wasn't working, turned fan to "on", no air from vents. Opened handler cover. Coils were cold/iced. I defrosted and cleaned with coil cleaning foam. Checked and cleaned drain line and dried the sensor. Still no air out of vents

. If I turn off unit at the switch. Then turn it back on, I can hear the thermostat click, and the a/c unit 'picks'... then the internal fins in the blower are moving. I hear a kind of whump ... whump ... whump like some motor is trying to engage but nothing is happening.

Even thought the fan inside the unit is spinning, no air blowing from the vents. Is it time to go outside and work on the compressor part or could it still be something inside at the handler? Its Friday after thanksgiving, trying to fix this myself if its possible, or at least know exactly what the problem is before I call in the "pros".

I have some electronics background and I have changed out the run capacitor ouside a few time. Usually if its that, the air does blow from the vents.

On 2020-11-20 - by (mod) -

Since your motor is working it sounds as if the problem is with the wiring or a switch or control

On 2020-11-19 by Mike

I have an electric motor for a bed to lift and lower but now it only goes one direction what could be the problem

On 2020-10-16 by (mod) - electric motor repair: re-winding, varnishing, etc.

Bruce:

Companies who are expert in or who provide electric motor re-winding services describe use of either varnish or a resin used to insulate the motor rewinding wire after repair.

Dreisilker describes four types of electric motor winding insulation methods; you'll want to see that guideline before buying anything. You'll want to match your winding insulation method and material. The four methods are

1. Dip and bake: electric motor windings are dipped in varnish and then baked in an oven

2. Trickle varnishing: the motor windings are heated and spun to distribute the varnish

3. Vacuum Pressure Impregnation (VPI) a vacuum pressure tank filled with varnish is used to fully impregnate motor windings and insulation with resin or varnish.

4. Ultra-Seal - the electric motor windings are impregnated with high molecular weight thermoset polymer resin.

- https://dreisilker.com/blog/4-types-of-motor-winding-insulation-methods/

You can see that some of these methods for electric motor winding insulation are pretty sophisticated and require special equipment. So you need to choose the method before buying varnish, another resin material, or thermoset polymer resin sealant.

Once decided there are quite a few suppliers of resins and varnishes for sealing motor windings, and nearly 500 products among which to choose, including some simple spray-on products; which and where you buy depend as well on the country in which you're working.

Just one example is a spray-on motor winding varnish from

• McMaster-Carr, 9630 Norwalk Blvd. Santa Fe Springs, CA 90670-2932, USA Website: www.mcmaster.com Email: la.sales@mcmaster.com Tel: (562) 692-5911
  
  

On 2020-10-16 by bruce - >Where do I buy all the insulation material for just one motor rewinding?

Where do I buy all the insulation material for just one motor rewinding?

hendricksonbruce399@yahoo.com

On 2020-09-13 - by (mod) -

Could be a burnt winding or failing bearing or of course, low voltage.

On 2020-09-13 by Eric Booth

single phase electric motor tripped earth leakage and after remaking connections, runs again but at reduced speed

On 2020-08-23 by Matt

I have a single phase 240v motor running an air compressor. When tbis moto 3rd is running my lights on the same circuit flicker. What could be causing this?
Is this a simple fix?

On 2020-08-07 by Nithyananda

What are the Reasons for Low motor running Amps(7.5A@245V) in 2HP single phase submersible Borewell pump set with start & run capacitor ??
Normal Running Amps :12.5A@245V

If main winding is faulty, and auxiliary winding is all right, of submersible pump set motor with start & Run capacitor, then what would be the Running Motor Amps as main winding is already faulty ? (2HP Rating, single phase pump-set )

On 2020-06-27 - by (mod) -

Lindy

Have you checked to be sure that there are no switches that could be out of order.

E.g. a start winding power may be turned off by a centrifugal switch.

On 2020-06-27 by lindylex

I have the following fan motor model # SFC1-500B, 120V 60HZ 1.35A 162W. I am trying to figure out how to repair it. This is a learning project and not sure how to get past this part.

The red color wire has no continuity getting to the windings.

I checked it from one of the prongs on the power cord.

The power cord is connected to a red wire that goes to a white wire that goes to the windings.

There is continuity to the white wire as you can see under the insulation that disrepair into the windings. I check the winding to see if there is continuity and I get none. I should be able to touch it with the multi-meter and get low resistance correct?

How do I check to see if the coil can receive power from the power cord? This seems like the most obvious way. If there a copper wire broken from the white wire located under the insulation?

On 2020-06-13 - by (mod) - blower motor won't run

Lak

If that motor is new and came with three other identical motors, and if it was wired properly but does not run, then the motor is defective, perhaps seized or with a manufacturing defect - not something we can decide from photo alone.

However above on this page we describe diagnostic testing procedures for such electric motors.

On 2020-06-11 by Lakshmipathi

Hi we got 4 new motors and one also not working it's blower type ,I am giving direct supply 220v not with blower set,for checking purpose but no one is rotating may i know the reason

On 2020-06-08 - by (mod) -

Mike

That sounds like a failed motor or a shorted control or circuit

On 2020-06-08 - by (mod) - why the service tech tries replacing the start or run capacitor

Right, Bob, that's why a service tech often "shotguns" a repair guess by swapping in a new cap.

Let me know how that works.

On 2020-06-08 by Mike

I have an Electric motor on air compressor that starts and runs for about 5 seconds and trips breaker. Tried on several different circuits.

On 2020-06-08 4 by Bob Abbot

I guess a replacement capacitor will be a lot cheaper than a motor, so I'll try that first and let you know. Thanks.

On 2020-06-06 - by (mod) - motor runs backwards

Yes that's possible.

On 2020-06-04 by Anonymous

hi and thanks for your reply. I have read the linked article and noted the possible reasons for my single phase motor going ACW rather than CW.

It may be that the fault/damage had already been done before I bought it but I can't see how the motor's start widing connections could have been reversed, as being one suggested possibility. As regards a failed electric motor starting capacitor, there is a small square capacitor close to the manual switch. If this was faulty, could it influence the motor direction?

On 2020-06-02 - by (mod) - electric lawnmower runs backwards

Bob

Let's start with diagnosing the cause and then we can select the cure for an electric motor that runs backwards. It may be that the motor was damaged or it may simply be a wiring error.

See details at ELECTRIC MOTOR RUN DIRECTION - backwards

after checking there let me know you you're progressing

On 2020-06-02 by Bob Abbot

My lawnmower, which I bought on eBay, is rotating the wrong way.

The single phase domestic electric motor has two terminals/spades which I swopped over but no change.

The motor should rotate clockwise, looking on the spindle, which ties in with motor fan and grass impeller configuration. There is a capacitor adjacent to the manual switch, if this item was faulty could it have any effect on rotation?

The mower does cut the grass, throws most of the cuttings into collection box but also scatters some around!
Would be grateful for any suggestions/solutions, thanks

 

On 2020-05-07 - by (mod) - humming electric motor causes

Lentikile

Humming motor without running is often a bad start capacitor or a seized motor,

also can be low voltage or overloaded motor.

On 2020-05-07 - by (mod) -

Anon

I don't know enough from your note to make a reliable guess at what's wrong with your motor, but yes, a motor winding sometimes opens up only when the motor is spinning.

On 2020-05-07 by Anonymous

I've tested continuity because the motor only has one capacitor ando the wiring seems fine.could it be that the windings are damaged?

On 2020-05-07 by Lentikile

If a single phase automatic pump motor just makeso sound without running what could be the cause

On 2020-03-05 by Anonymous - squealing 100V induction motor

Jimbo

That sounds to me like a wiring error, damaged or shorted wire, or perhaps a lost or bad start capacitor. It's possible that dis-assembly and re-assembly nicked a wire or connector belonging to the start cap.

On 2020-03-05 by jimbo - bad bearing in electric motor

My 100v induction motor was squeling but running and starting fine. I found a bad bearing on the front so I change both front and rear bearings.

Everything turns very smoothly by hand but when I plug it in it now only buzzes and blow the breaker.

Can't figure what I did wrong. All went back together as originally. Finding it hard to believe it is the capacitor or centrifugal switch or contact since it ran before the bearing change. Ideas?

On 2020-03-04 by Anonymous - what to check when electric motor overheats and shuts off

Jessie

I can't say with certainty but I think your electrician will look at

- actual voltage being delivered to the high speed terminals

- pump wiring connections

- pump loading, bearings, water supply

Meanwhile, don't hook it up as you risk a fire (and may have damaged the pump)

On 2020-03-04 by Jessie Higgins

I have a single phase 220 Dual speed pump and when I hook the high speed side up it runs for about 5 seconds and then starts to smoke and shuts off but if I hook up the low side it runs fine why is this

On 2019-11-23 by (mod) -

Les

Watch out: What you describe is very dangerous risking an electrical shock injury or worse.

You should unplug that motor immediately. Most likely the switch has either failed internally or is shorted internally. It's possible that the wires to the switch have become shorted together.

On 2019-11-23 by Les

The 230V Rockwell motor on my table saw runs with the switch on or off. What could be the problem?

On 2019-10-11 by (mod) -

Wally

If the problem wear a switch that needed to be reset then I don't think you would see any movement in the fan when you turn power on

On 2019-10-11 by Wally

Motor doesn’t start when relay closes. Sometimes fan moves ever so slightly. Changed capacitor but no changed. I haven’t pulled the motor assembly out from the enclosure yet. Could it possibly have a resetable overload switch?

On 2019-08-16 by (mod) -

COuld be a bad start capacitor

On 2019-08-16 by Bruce

1hp air compressor. The motor just humms when you turn it on. You can freely turn the pulleys when this happens. Maybe like starting out in overdrive going uphill.

On 2019-07-30 by (mod) - how to check for bad electric motor bearings

It sounds to me like you want the motor tested.

That's really would be less than the cost of arbitrarily replacing the motor. There is something you can do first which is to remove the motor completely and simply confirm that the motor drive shaft will spin freely.

If the drive shaft doesn't spin easily or if it wiggles in its bearings, or if there is a lot of end play when you move the motor drive shaft parallel to its axis then the motor is probably damaged or its bearings are shot.

A motor rattling noise or vibration may also be a sign of failed motor bearings.

See details at RATTLING & VIBRATION noises from A/C or Heat Pump System

On 2019-07-30 2 by Tommy

I have a Waterco Aquanature 50xl heat pump for my pool.

After a normal cycle the fan stop, after the fan tries to start, but it takes 2-3 times before she gets going again at full speed.

I changed both capacitor (10uf 370v) and i still have the same problem. Anybody ever heard of that problem before ?

(relay good too) i thing it could be the motor but it's very expensive for just a test ? any help (motor 1/8hp 825rpm 208-230) Thnx for your help

On 2019-07-02 by (mod) -

Tobey:

Checking a condenser fan motor with a VOM or DMM in Ohms mode:

On a multi-speed fan you'll find different resistances on different wires checked against the white fan wire - for an A/C or heat pump condenser fan.

Beyond that - which is model specific - a resistance of zero across the motor usually means that there is an internal short, perhaps in the windings.
and infinite resistance typically means that there is an open connector or open winding.

On 2019-07-02 by Tobey

What is a condenser motor fan supposed to read when you ohm out

On 2019-06-19 by (mod) -

Ron, if we assume the motor isn't overloaded then it sounds as if the motor is overheating, perhaps from a bad bearing. Check first, though, for low voltage.

On 2019-05-23 4 by Ron

Small AC capacitor start motor. 1/2 hp. It runs fine for ten minutes, then stops running. Then buzzing trying to start again, but it cant. The start capacitor was burned out when I got it, but I replaced it.

On 2019-04-26 - by (mod) -

It sounds to me as if the motor was designed to increase its output torque under load. That's something that you would expect a motor for a treadmill to do. Have you tried an independent speed controller?

On 2019-04-25 by Dave N.

I have taken a properly operating treadmill apart to repurpose the motor ,circuit board, sliding speed controller to operate a pottery wheel, the project is successful except as I'm putting a drag on the spinning wheel while shaping the pottery the motor seems to try and compensate for the reduction of rpm ,

and as I ease pressure on the pottery ie reduce drag the wheel speeds up much faster than the speed controller is set at , then slows to original set speed, this doesn't work for pottery as it slings the clay everywhere, I hope you have an answer for me, thx

On 2018-07-24 - by (mod) -

I'd expect your technician will look for

- variations in supply voltage
- a failing bearing
- a failing or loose capacitor or capacitor wiring connection

On 2018-07-24 by Jim

2 speed motor in evaporative cooler occasionally jerk in low but runs great in high speed. Only does it occasionally.

On 2017-09-28 by Dave

My electric lift motor only goes one way...will not reverse. Replaced capacitor and Levitra. Motor was under water.

On 2017-06-23 by O. Roman

I had previously posted a question on the same subject (Question: Furnace air blower jerks when turned off).
I have replaced the squirrel cage and the motor and yet the problem remains. The problem happens as the motor cycles off while cooling on auto. The motor shakes as the thermostat cycles it off. And it's a brand new motor.
Don't know what else to do.

Thanks.

Question: heat pump air handler motor diagnosis

(Jan 31, 2015) Anonymous said:

heat pump air handler variable speed works, warm air comes out vents. here's the serious problem though. when i go to high speed it runs for 20 seconds, then it goes to low speed for 20 second or so. this cycle continue and lately the high speed act like it wants to quit. any help would be appreciated.

Reply:

Anon I'm not sure if the problem is in the motor itself - sounds more to me like a control or relay problem.

See BLOWER FAN OPERATION & TESTING

Question: damage to electric motor if swap hot and neutral wires

(Feb 7, 2015) lynda-david@talktalk.net said:
Ran my water pump with the live and neutral reversed will his have done any damage to the motor

Reply:

Lynda

Some AC motors may work normally when wired backwards; but I don't know what motors and controls (and starting capacitors) your system has installed.
If the pump still runs and no breakers or fuses blew you may be just fine.

For many motors, in the short run no damage may have occurred to the motor but the wiring was unsafe risking electrocution, and also risking damage to the motor controls and switches.

Question: electric motor starts but trips breaker after 30 seconds

(Feb 9, 2015) Les said:
I have a 3/4hp cap start ac motor which starts fine but trips the breaker after running 30 seconds or so. does not get hot to the touch and capacitor tests within specs. Any ideas?

Reply:

Les,

I'd expect an electrician to look for high current draw which would confirm that the breaker is doing its job and there's a motor or wiring failure. The motor may have a failed run winding or bearing; Or the driven equipment could be binding causing excessive motor loading.

Also check the supply voltage.

Safe would be to leave it off of course.

Question: synonyms for electric motor capacitor: condenser, and other terms

(Feb 11, 2015) Soham said:
can sometimes condenser be called a capacitor in case of water pump

Reply:

Yes Soham in some areas people use the term "condenser" where in most articles at InspectApedia we use the term "capacitor"

Synonyms for capacitor include: condenser and electrical-condenser.

Also I'd include

electrolytic capacitor

electrolytic condenser

Leyden jar, (and mis-spelled Leiden Jar)

trimmer or trimming capacitor

Capacitors store an electrical charge and release it in a nice big zap.

Other electrical storage devices are various types of batteries or storage cells.

Other "synonyms" posted at some thesaurus websites are nonsense and include very generic terms like CRT AC and Circuit that simply do not pertain.

Question: motor starts slowly then stops

(May 13, 2015) Solomon said:

My 2horsepower Electric moter for a centrifugal pump at times starts and runs slowly for few seconds and stops. At times when switched on it shotdown other electric motor in the system. what shoud I do?

Reply:

Solomon

I'd check the current draw of the motor - it sounds as if a failing motor (or possibly a hard-starting motor due to a bad start/run capacitor) is the trouble.

See HOW a STARTING CAPACITOR WORKS

Question: Weather King Furnace motor trouble vs cycling on and off?

(June 15, 2015) jim dyson said:
weather king furnice outside unit & fan run continuously inside blower cycles on & off does not cool the house

Reply:

Sounds like a refrigerant or a control problem. You need an on-site service technician to sort this out, Jim.

Question: Spa pump motor won't run if stops in some positions

(June 16, 2015) Mike said:
I have a 5 hp spa pump motor that fails to self start if the rotor is positioned anywhere within about a 90 Degree segment of the entire 180 degree rotation. In other words if it stops at anywhere from 12:00 to 3:00 it will hang and not begin spinning without a manual assist.

Anything outside of this arc and it works fine. We just rebuilt this motor with new bearings, start and run caps. We even hooked another start cap in parallel with the original with no help. Any idea why this is happening?

Reply:

Mike

Do you think it's possible that the motor has an open start winding? Also, double check that the start / run caps are working - that the replacement parts were ok

Question: HVAC motor keeps switching between heating & cooling modes

(June 21, 2015) robert said:
my fan motor on my central heating and air conditioner keep witching back and forth. the air flows out the top to cool the compressor but the next time it come on the motor turn the other way and pull the air in causing the compressor to over heat

Reply:

This is a control problem not a problem with the electric motor, Robert

 

Question: trouble with re-built electric motor

(July 3, 2015) Mike said:

We rebuilt two identical motors. The other is fine. We swapped all the caps between the motors also with no effect on the problem one. I thought we might have overheated the winding but it looks brand new and has no smell of burning inside.

If the start winding was open, why does the motor start as long as it doesn't start from that arc? I was wrong about that angle as it is 90 degree of 360 degree. I suppose we'll tear them down again and check resistance. Could the centrifugal start up switch be at fault?

Reply:

Very interesting Mike. Could a winding be opening when the motor spins - or some other part moves?
Those defects can be hard to spot by mere visual inspection.

(Sept 29, 2015) Mike said:

I lost the link to here until now. The spa motor with the start problem (July this year). We tore it down again checking all we could and polished the kick out switch contacts with 2000 grit sand paper. This reduced that 90 degree no start arc to about 10 degrees.I think it's resonable to assume that the switch is the problem. Now to figure out where to buy one.

Question: Diagnose boat lift motor - popping noise

(July 7, 2015) Eric said:
I have a boat lift A/C 1hp leeson motor, 1phase, i control on a barrel switch, when i start and stop the motor i hear a loud pop, sound like arching, the lift seems to work fine other then the noise, any ideas?

Reply:

Look for a shorting switch or wire - an unsafe condition.

Question: motor shuts off after a minute - gets hot

(July 17, 2015) john said:
Single phase motor runs for a min and shuts off i pulled it out of the furnace and hooked it up and does the same thing gets super hot and turns on for 3 secs shuts off for 10 and repeats whats going on here

Reply:

Could be a failed bearing or winding causing overheating that shuts the motor off via a built-in thermal protection switch.

An electrician would probably check the supply voltage and the current draw.

Question: electric mixer motor stops under load

(July 26, 2015) taffy said:
electric mixer will run if i hold my finger on start button but stop when released also when it does run if load it stops

Reply:

Sounds like a failing motor or bearing, less likely, low voltage.

Question: Coleman air compressor trips circuit breaker

(Nov 9, 2015) Mike Bolden said:

Coleman air compressor trips circuit breaker on restart. 5hp belt driven Mod MP0502513. Did not run at all. Caps tested bad -replaced. Runs now. On startup, it reaches cutout and stops.

On restart, it reaches cutin and starts but after about 2-3 seconds, it trips the circuit breaker. It has a new pressure switch w/ unloader and a new check valve. I'm thinking motor now.

Do these motors have a centrifugal start switch in them? It may be slow to operate on restart holding the high current draw too long and causing breaker trip. Any help is appreciated.

Reply:

Mike

Yes some motors (I don't know yours) include a centrifugal switch to cut out the start cap when the motor gets up to speed.

Do you think the motor itself could be seizing? If it's disconnected how hard is it to spin?

Also check that the air compressor is not trying to start against a high head pressure.

Question: electric motor overheats at low speed

(Nov 21, 2015) Aaron said:
Electric motor overheats on low speed

Reply:

Aaron

If your motor is not designed to run at variable speeds then the problem may be

- low voltage
- failed control
- faulty wiring
- internal damage in the motor
- bad start/run capacitor

Question: Spa motor hums then shuts off

(Feb 14, 2016) Dan said:
My spa motor doesn't seem to have capacitor, just a small contact panel. Motor hums then shuts off. Is that contact panel a capacitor?

Reply:

Dan I'm not sure what your system has - not all motors use a starting capacitor. But if the motor hums and then shuts off certainly it's having trouble starting.

The problem could be that a bearing is seized or that voltage is abnormally low. I suspect a seized motor bearing as that's common with spa motors exposed to leaks and corrosion.

Question: Belt sander motor stuttering start

(Mar 6, 2016) john said:
the motor on my 1'x42' belt sander has a capacitor lately when I turn it on starts an stops 4 or 5 times before running at speed. Is this the capacitor?

Reply:

John
It depends on motor type:

A motor may have a start and run cap of which either or both have failed;
A motor may have a centrifugal switch that switches out the start cap when it gets up to speed - also failed.

Or there could be

- a loose wire

- a binding bearing

- a loose or failing switch

- or something else I've not considered

See if you can turn the motor freely by hand when it's not connected to anything else (and power is off) - that may point to or away from a bad bearing.

Question: electric motor won't start, drawing high amps but spins freely

(Apr 14, 2016) electric motor wont start said:
Electric motor wont start, draws 27.5 amps and wont turn. Motor is free and can spin by hand. It is a 1/2 hp lifttech motor. Any ideas what could be wrong?

Reply:

I suspect a bad start/run capacitor or an open winding. If the amps draw you cite exceeds the starting amps on the motor data plate then it may be shorted internally. That seems most likely.

Question: motor data plate does not show startup amps

(Apr 14, 2016) Doug said:
The data plate has no starting amps listed. The FLA 6.3, so would the 27.5 not be pretty close to the start current?

Reply:

Doug: you should be able to find the specs of the proper capacitor you need from the wiring diagram or instructions for your lift, and most likely you can find a generic replacement that will work. For **Example** check out the Universal 24889 - R17058571-BH Ballast Capacitor - to see if that matches your specs.

Question: Blower motor does not run properly

(Apr 26, 2016) Jose said:
BlowerMotor works when thermostat is in "on" position and with switch in the middle of "warm" or "cold" (off position). After a couple of hours I can move the switch "warm-cold" to "cold", leaving the other switch in "on", because if I move it to automatic blower stop, and I have to start all over again.

Forgot to say that already I changed the thermostat and the capacitor.

Reply:

Sounds as if you are not setting the thermostat fan switch to a normal position. It should be fully in Heat Cool or Off. Not sure what "other" switch you are leaving on nor just what is the question here.

Question: electric lawn mower won't run

(May 2, 2016) Anonymous said:
Power to elec. Motor on lawn mower but still won't go

Reply:

See ELECTRIC MOTOR DIAGNOSTIC GUIDE for help in diagnosing and fixing the trouble

Question:

(May 28, 2016) Anonymous said:
How to change direction of notoriously

Reply:

Anon I think your spell checker has tripped us up.

Question:

(June 4, 2016) Anonymous said:
ac motor not getting electrial

Reply:

Check for power at the supply connections. I'd trace the circuit backwards to find the open wire or switch, or forwards from the breaker or fuse.

See ELECTRIC MOTOR DIAGNOSTIC GUIDE for help in diagnosing and fixing the trouble

Question: Furnace air blower jerks when turned off

(Aug 5, 2016) O. Roman said:
Hello. I have a furnace air fan blower with blade housing that continually jerks when it turns off. I have the thermostat set to auto and every time it turns off it jerks. The motor is screwed on tight onto the housing but the motor continues jerking on auto shutoff. Twice the motor has broken one of the three metal supports that attaches it to the housing.

And twice I have had to weld this back onto the motor and screw back onto the housing.

After the last weld the motor will jerk every now and then. What could it be? An electrical surge right before the thermostat cuts it off? Thanks.

Reply:

I'd look for a loose fan pulley of motor or fan bearing and for other loose parts, a loose electrical connection, or a stretched blower pulley belt (if your motor is not a direct drive unit). Also a motor drive shaft misalignment could be torquing the system parts at an angle.

(Aug 9, 2016) Anonymous said:
Thank you. I'll check on it and let you know what I find.

Question: Drill press motor cuts in and out

(Aug 25, 2016) Ivan said:
Drill press motor starts and runs, then it appears the start switch cuts in and out.

Reply:

Look for a bad switch or wiring connection first. Check for a difference in behaviour if the drill press is under load.

Question: burnt electrical wiring

(Sept 6, 2016) Tonya Kahle said:
What do you do when your ac wiring is burnt up?

Reply:

Watch out: you are describing a dangerous condition risking electrical shock, death, or fire.

Check for a bad circuit breaker that is not tripping when it should, then check for a short circuit in the electrical circuit for the system you are debugging.

Search InspectApedia.com for FPE CIRCUIT BREAKER or ZINSCO CIRCUIT BREAKER or BAD CIRCUIT BREAKER to see examples of these failures.

Question: Bad electric motor on Emersion fan - wiring question

(Oct 6, 2016) ANGEL CERECRR said:
I have a emersión fan motor,got 4 wires,two white,a brown And a orange,how i conecct to work con a convencional fan?

Reply:

Angel,

Let's start by identifying the product brand and model, then we can find the wiring diagram for your model that identifies the function and connections of each of the wires you cite.

Question:

I stripped and cleaned an electric motor on reassembly it spins backwards Why?

Reply:

Please see ELECTRIC MOTOR RUN DIRECTION to diagnose and repair an electric motor that is running backwards.

Question: Aerator motor stopped working

(Oct 27, 2016) Richarf said:
I have a aerator motor that went down and stopped working. I tried to plug it directly into my outside outlet and it trips the outlet as soon as it's plugged in. I checked wiring and motor runs fine with the ground wire disconnected. What's the cause of this?

Reply:

Watch out: Richard

Sounds as if the motor or its wiring are electrically shorted to ground. DO NOT USE IT as doing so risks death by electrocution. The wiring needs repair - perhaps internal to the motor if you don't see the damage outside.

Question: are there different test procedures for DC electric motors?

ELECTRIC MOTOR DIAGNOSTIC GUIDE describes a lot of diagnostic test procedures for A/C electric motors such as those found in air conditioners, heat pumps, washing machines, clothes dryers, condensate pumps, well pumps, even garage door openers. But what about direct current motors such as used by hobbyists and in some automotive or boat applications?

Reply:

Hobbyist LB Miller has described the design and function of a simple test fixture useful for determining the electrical resistance of DC motors by providing a 1A current to the motor and measuring the voltage drop across the motor, thus giving motor resistance in milli-ohms. Note that his approach is for DC motors. [33]

Question: table saw motor hums, doesn't run

(Feb 18, 2014) Anonymous said:

I have a Bosche table saw and the motor has malfunctioned. It is a 120volt motor. When switched on it "hums" but does not spin. What could be the cause of this? Is it repairable?

Reply:

Anon,

I would remove the motor from the saw completely - for safer testing.

With the motor out of the saw, see if you can rotate the shaft by hand.

If you can then the shaft is (probably) not bound and the problem may be a bad start capacitor (if there is one). There are also some simple tests in the article above that you might want to try when the motor is out of the saw.

Question: blower motor buzzes and won't start if it's hot

(Apr 7, 2014) Jan said:

My furnace 1/2 hp blower motor starts and runs quietly from cold but will not start and makes a loud buzzing sound when hot until the thermal breaker kicks in. The motor is hot to the touch when this happens. It will go through one heating cycle, turn off and not restart. BTW the motor is only 1 yr old.

Reply:

Jan,

Buzzing is often a bad relay, switch, or control board. Hot to touch motor sounds like a failing motor or motor start capacitor, possibly showing up when the system is hot. It's time for a call to your heating service tech. Let us know what s/he finds as it will surely help others.

Sometimes a hot electric motor won't start because the motor shaft is binding in the bearing.

Sometimes a hot electric motor won't start because at the higher temperature a winding or electrical connection has opened.

Question: AC not working to cool the home - change the blower motor?

(May 14, 2014) Jaime (from Huntington WV) said:

Hi! In 2010 we replaced our outside central air unit, without replacing the furnace inside. The forced gas heating inside works great for heat in the winter, but in the summer when it gets humid, or newer AC in combination with our older fan/motor inside the house do not work well together.

I have very cold air coming out, but by the end of the day when the thermostat is set on 69, it just keeps going up and up to about 71.

From what I have been told, the humidity makes the air thicker which in turn the old fan/motor in the furnace part can't handle the cool air from the new AC, which in turn my duct work under the house sweats terrible.

Can I replace the motor in the house with a newer/more powerful motor without replacing the entire furnace inside? I hope you understand what I meaning. =) Thank you! Email me or comment back BillandJaime2004@gmail.com

Reply:

would look for an operating problem, possibly improper refrigerant charge, or dirty filter, that is causing the coil to freeze - that could explain the reduction in cooling capacity as the day wears on. Look for frost or ice on the cooling coil.

Another direction of diagnosis: if the system is oversized then it will cool the home too quickly, failing to adequately dehumidify.

Question: cooker hood motor hums but runs if I give the fan a spin

(June 16, 2014) Robert holt said:

Hi. I have a cooker hood motor that hums when fan speed is selected but does not turn. I have taken it out from the impeller casing, and if I give ithe shaft a quick turn whilst power is on, the motor spins, but as soon as turned off, does not restart on button. Any help please
Thanks Rob

Reply:

Robert,

It sounds as if the fan motor needs a new start or start-run capacitor.

Question: Carrier air handler blower motor repairs - noisy, intermittent run

(July 23, 2014) B said:

Hey guys - I'm having a problem with the blower motor in my carrier air handler. I keep it oiled regularly every yr to 2 yrs as equipment suggests. Started squeaking on me when we turned our ac on this summer.

After cleaning / lubricating the motor, restarted ac and it ran fine for 4-6 hours then wouldn't not kick on when tstat showed a higher inside temp then set at. I check ed the motor and all was clear and well lubed and restarted.

Ran OK for a period then same issue. Motor became noisy again and will only run intermittently and then get noisy and shut itself down. Is this a case of bad bearings / windings in the motor or could it be a wiring issue? Any helps would be great. Thanks in advance.

Reply:

B

Check first that the blower assembly itself is spinning freely, not binding, and doesn't have worn bearings.

Then consider that the motor may be failing internally, possibly a bad bushing or bearing.

You might extend its life with a hard start capacitor kit.

Question: how to oil an Emerson K55hxkwa-9803

(July 23, 2014) Jeff Wilmsmeier said:

Can you oil a Emerson K55hxkwa-9803

Reply:

Jeff I had trouble finding a manual for this fan motor online too - so I don't know the answer.

Look closely at the motor assembly. Oil ports will be obvious, often capped with a hinged cap or a hole facing up marked "OIL" on the steel body of the motor.

Or send us some sharp photos of all sides of the motor and we'll comment further.

See ELECTRIC MOTOR LUBRICATION for detailed advice

Question: free AC inspection, said working perfectly, added refrigerant, recommends zero resistance filter

(Aug 22, 2014) Blower fan internal heat switch cuts motor after 30 min. said:

Had an HVAC CO provide a free inspection. A/C was working fine for prior 1 yr. Tech added refridg. and change dirty filter in attic. Now Blower Fan only runs 30 min and cuts off. Back on in 20 min.

After 4-5 more visits, Tech wanted to sell me a new A/c at $8-$10,000. Found bent blower door and improper/wrong filter. Also, refridg. was 2 lbs low so none had been added by Tech.

What type of Blower Fan filter provides "0" airflow resistance...?

Thank very much,
New motor, cage bearings oiled and spinning freely. New fan belt. I removed the "new" filter and motor is now running cool enough that it is not cutting off from overheating. So I guess I am looking for a filter with no resistance.. any thoughts?

Reply:

Blower

I'm surprised that a tech would add refrigerant if the system was working properly - though we should keep in mind that a skilled HVACR tech may still not be an English major - so may not have explained what s/he was doing or why. Now I'm not sure what's wrong, but that offer of a costly new system is disturbing.

Ask to be shown and told what expensive parts are shot and how that diagnosis was made.

Then call a second HVAC company and ask for a second opinion before we accuse anyone of something further. If your system is an old one it might be at end of life, but working up until the time the tech touched the system is indeed worrisome.

A filter that gave zero air resistance would probably also not filter air passing through it.

A very very low air flow resistance air cleaner that is widely used is an electrostatic air cleaner. However usually we see these used in combination with a more conventional particle filter.

Kudos on getting the new motor going.

There are no zero-resistance air filters - since filtering will always create some resistance. But filters are rated for flow resistance.

About the lowest flow resistance type is an electrostatic air cleaner. Typically those are preceded by a washable filter and some by a low-resistance fiberglass or other paper filter.

Take a look at AIR FILTER OPTIMUM INDOOR

Question: Nordyne heat pump blower motor voltage checks

(Aug 30, 2014) Mike said:

Blower motor in Nordyne heat pump will not turn on. I have tried overriding thermostat but still won't kick on. I checked for voltage at transformer (240v-28vac) and looked good. I wanted to know how to test the blower motor relay. I thought I should see ~240vac across black and white wires of motor.

Reply:

Mike

Check the motor data plate - it more likely is a 120V unit.

A 28VAC transformer output is more likely being used to operate the blower's controls.

Well Pump Motor Diagnosis: grounded pump motor vs. air leaks in well piping

(July 18, 2015) Allen said:
Thanks for your prompt reply. After checking the voltage, the main and start windings are within specs. I did however receive a reading suggesting the motor is grounded. Could a damaged wire in the well casing be causing the symptoms?

Reply:

David:

Double-faults can occur but Occam's razor says we should look first for the simplest explanation as it's most likely.

Is it possible that during the repair a pipe connection simply was not perfectly tightened. For example I've found air leaks into piping (and thus potentially loss of prime) when a hose clamp on plastic piping at joints was not quite tight.

A problem is that air leaking in to the lines may not be so easy to detect unless your system has a clear plastic water filter in which you'd see bubbling and frothing. But you might start by tightening or double-hose-clamping every accessible connection

...

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

Or see ELECTRIC MOTOR DIAGNOSTIC FAQs-2 - more questions & answers about fixing electric motors

Or see these

Recommended Articles

• ELECTRIC MOTOR DIAGNOSTIC GUIDE - home
  • A/C ELECTRIC MOTOR COMPONENTS
  • BURNED-OUT COMPRESSOR
  • CAPACITOR TYPES, for MOTORS
  • CAPACITORS for HARD STARTING MOTORS
  • CHATTERING RELAY CONTROL SWITCHES
  • COPELAND ELECTRICAL HANDBOOK [PDF]
  • ELECTRIC MOTOR 3-PHASE MOTOR SELECTION
  • ELECTRIC MOTOR 3-PHASE TROUBLESHOOTING
  • ELECTRIC MOTOR CENTRIFUGAL SWITCH or PTC PRD
  • ELECTRIC MOTOR DATA TAG
  • ELECTRIC MOTOR HORSEPOWER & CIRCUIT WIRE SIZE
  • ELECTRIC MOTOR LUBRICATION
  • ELECTRIC MOTOR NOISE DIAGNOSIS
  • ELECTRIC MOTOR OFF on RESET
  • ELECTRIC MOTOR OVERHEATS
  • ELECTRIC MOTOR OVERLOAD RESET SWITCH
  • ELECTRIC MOTOR RUN DIRECTION
  • ELECTRIC MOTOR START SWITCH
  • ELECTRIC MOTOR TESTS
  • ELECTRIC MOTOR WIRING DIAGRAMS & GUIDES
  • ELECTRIC MOTOR WON'T START / RUN
  • HARD STARTING COMPRESSOR MOTORS
  • HARD STARTING ELECTRIC MOTOR CAUSES
  • OIL BURNER NOISE DIAGNOSTIC INDEX
  • RESET BUTTON, ELECTRIC MOTOR
  • TIGHT or SEIZED AC COMPRESSORS
  • WATER PUMP PROTECTION SWITCH

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