Electric motor test & repair guide:
This article 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.
InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
- Daniel Friedman, Publisher/Editor/Author - See WHO ARE WE?
In this article we provide a diagnostic guide to determine and repair problems with 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.
At left our photo illustrates the motor as typically found in a direct-drive HVAC blower or air handler assembly. More about this air handler fan i
s at BLOWER FAN OPERATION & TESTING.
[Click to enlarge any image.]
Watch out: if you are not trained in safe electrical wiring and test tool use you should not fool with electrical motors or wiring. You could be shocked or killed.
While our page top photo shows the red reset button most clearly, the reset button on the motor at left may be harder to spot. Sometimes the reset button on an electric motor is hard to find, and sometimes there is no reset button!
Fatal Shock Hazard Warning: Inspecting electrical components and systems risks death by electrocution as well as serious burns or other injuries to the inspector or to others. Do not attempt these tasks unless you are properly trained and equipped.
See DMMs VOMs SAFE USE OF for help in making safe use of electrical test equipment before you start poking your meter probes into anything.
Before discussing how to diagnose air conditioner or heating system electric motors let's be sure we know what motor parts might be involved. (Or skip right to Table A if you prefer).
Photo: electric motor on a modern oil burner.
The electric motor has quite a few parts if examined in detail, switches, wires, possibly capacitors, oiling ports and more, but there are four basic parts to every HVAC electric motor:
In addition to the basic electric motor components above there are two other features to know about when troubleshooting a motor.
In our photo at left you can see the notation on this electric motor data tag indicating the the motor is non-reversing and rotates counter-clockwise - designated by the words CCW ROTATION (red arrow).
If you enlarge the photo [Click any image to see an enlarged, detailed version] you will see text above the red arrow noting that this is a NON-REVERSING motor.
See ELECTRIC MOTOR RUN DIRECTION
The blue oval marks the motor's rotating speed - 3450 RPM - this is a high speed oil burner. Older oil burners and equipment motors run at 1725 RPM.
Some HVAC equipment uses a variable-speed electric motor, often an ECM or “electronically commutated motor” that uses electronic controls to control and/or to vary the motor speed.
The green rectangle marks other useful data in the data tag for this motor, made by Emerson Electric in St. Louis MO. This is a 1/7 hp motor, designed for 115VAC, drawing 2.35A.
These data are helpful when diagnosing electric motor problems: using a DMM or VOM we can detect unusual current draw above that 2.35A as a sign of trouble and we can check that the voltage level delivered by the electrical supply is close to 115VAC 60 cycle current single phase.
The motor's model number (SD55GYJTK-5181 in this example) is useful when replacing the motor or contacting the manufacturer for assistance.
An Electric Motor Time Rating designation is specified as CONT (continuous duty) - this motor is able to run continuously without damage or overheating under normal conditions.
A temperature rating (40C) and other data are given as well, including an explanation that this motor is. thermally protected and that should the motor's thermal protection switch trip off the user needs to press the red button.
See ELECTRIC MOTOR OVERLOAD RESET
This motor's data tag also includes oiling specifications indicating the required lubrication schedule, discussed
Watch out: when buying replacement electric motors, fuel units, and blower fan assemblies to be sure they all are compatible.
For example on oil fired heating equipment, the oil burner fuel units (the mechanical heating oil pump driven by the oil burner electric motor via a coupling) can be purchased as CW or CCW devices. All three components have to be designed to rotate in a common direction:
If the fuel unit is not rotated in the proper direction the heating appliance won't run - it won't receive fuel, and the driving motor and coupling parts may be damaged.
If a squirrel cage blower fan on an oil burner or inside of an air handler is spun backwards it will not move much air and equipment will not function properly.
See ELECTRIC MOTOR RUN DIRECTION
Watch out: when ordering a replacement ECM variable speed motor, such as a constant torque variable speed ECM motor often used in HVAC equipment you should take care to match the specifications of the original motor.
The programming of the electronic control module that controls the motor speed and torque is done at the factory - it's not something you adjust in the field.
For article loading speed we have moved this data
Details are at ELECTRIC MOTOR OVERLOAD RESET - separate article.
The start switch connects power to the start winding to start the motor spinning. This feature is necessary because depending on the position in which the rotor stopped when the motor last turned off, the rotating electrical field created by the run winding can't start the motor.
At CAUSES of HARD STARTING ELECTRIC MOTORS we explain how a failed starting capacitor OR depending on the motor design, a bad centrifugal switch can prevent a motor from starting.
A trained service technician may sometimes diagnose a failed start winding or failed start switch (centrifugal switch) by spinning the motor manually (potentially dangerous!). If the motor keeps running we suspect a bad start winding or bad start switch (see diagnostic table details
at Table A: 14 THINGS to CHECK (in order) if an A/C Electric Motor Will Not Start.
When the electric motor has reached about 75-80% of its full speed the centrifugal switch opens, thereby disconnecting AC electrical power from the start winding. Power was already connected to and remains connected to the run winding.
So if the motor will start but won't keep running, we suspect a bad run winding or bad wiring to the winding.
For electric motors used in most HVAC applications motor full speed is usually 1725 or 3450 rpm, though some equipment may use variable speed motors as well.
The centrifugal switch will open ("throwout") at about 2800 rpm for a 3450 rpm electric motor, and the centrifugal switch will open at about 1400 rpm for a 1725 rpm electric motor.
See more details at ELECTRIC MOTOR CENTRIFUGAL SWITCH or PTC PRD
Reader Question: 12/22/2014 sparks when motor is running said:
When a table saw is turned on I see sparks... what is the cause and how to fix it
Sparky,
Some sparking is normal within many electric motors including table saws and drills, but no sparks ought to be seen exiting the device or its motor for obvious safety reasons.
Typically when I've seen sparks spraying out of a drill or table saw I've found that the motor brushes need replacement. A burned commutator in the electric motor is often the root problem. Some light cleaning of the commutator may be needed. Take care not to score it. Remove the motor armature and sand it with very fine emery paper. Inspect the armature while cleaning it
Not all Electric Motors use a Starting Capacitor and/or Centrifugal Switch: here we describe (in oversimplified terms) 8 Common Electric Motor Designs.
Split-phase motors divide a single electrical current phase, sending it through two different windings that produce an electrical effect similar to motors run by a two-phase current source, producing a rotating electrical field to turn the motor.
Still other electric motors use the rotating magnetic field produced a two-phase or three phase design both to start the motor and to keep it spinning.
In a split-phase motor the stator uses two separate windings: start winding (smaller diameter wire) and a run winding (larger diameter wire). The start winding has higher electrical resistance than the run-winding, and it will be close to the top of the stator's core.
The run winding will be located near the bottom of the stator and will have the lower resistance of the two windings. The two windings are connected electrically in parallel with one another, as you can see in our sketch.
This type of stator can be used in both capacitor-start, capacitor run motors and in capacitor-start, induction-run motors.
The electric motor's stator contains four electrical poles, and the start winding is always located at 90° from the run winding. As electrical power is turned-on to the stator current will flow through both the start and run winding at the same time, but because of the higher resistance of the start winding, its current flow is more in-phase with the source voltage than will be the current flow through the run winding.
Therefore, the current flowing through the run-winding will lag behind the current flow through the start winding (due to inductive resistance).
It is the fact that there are then two flowing currents that are out of phase with one another that a rotating magnetic field is created in the stator.
The rotation speed of the magnetic field depends on the number of poles in the stator and the frequency of the source voltage (e.g. 60hz or 50hz). Several sources give a simple formula for determining an electric motor's rotating speed:
Speed = 120 x Frequency / Number of Stator Poles, or S = F/P.
Using the U.S 60Hz standard, we can calculate that a 2 pole motor should spin at 3600 rpm. (S or 3600 = 120 x 60 / 2)
Testing a blower fan motor winding: referring to the electrical diagram for your equipment, unplug electrical connectors at the fan motor.
Measure the resistance between each lead wire with a multimeter or VOM. The multimeter should be set in the X1 range.
For accuracy, don't measure when the fan motor is hot, allow it to cool off.
Test to determine if a motor winding (start winding or run winding) is not broken (open) or shorted (closed).
This test can be done on most household appliance motors including both single-phase and three-phase electric motors.
With the VOM set to the most-sensitive resistance or ohms scale (R x 1), and with the meter zeroed, check the resistance between the motor winding leads (you may need to check the motor's wiring diagram to be sure you're checking in the right spot).
Watch out: when measuring resistance at very low levels, a poor connection with your probe or even having your finger in the circuit will foul up the reading's accuracy.
Watch out: some damaged motor windings will test out just fine on the bench with the motor disconnected completely, but when the motor begins to spin a damaged wire in the winding may, due to the centrifugal force of rotation, open, causing the motor to run poorly or to stop completely or to chatter.
More detailed VOM tests on motor leads and windings are given in our diagnostic table found
at ELECTRIC MOTOR DIAGNOSTIC GUIDE
At BASIC ELECTRICAL TESTS for BURNED OUT COMPRESSOR MOTORS we give more details about resistance levels to expect when testing an electric motor.
If your motor uses a start/run capacitor, the capacitor could be defective.
If inspection by eye shows a capacitor that is bloated, burned, deformed, it needs to be replaced.
If by eye the capacitor looks ok it might still be defective.
With the capacitor disconnected from the motor's wiring, with your VOM probes on the cap's leads (test start and common, then run and common separately if the cap is a combined start/run device) you will see the resistance rise from a low number as the capacitor begins to charge, driven simply by the power source in your VOM itself.
Watch out: let the capacitor bleed-down for 10-15 minutes before trying to repeat this test or, as it still holds a charge your test will be in-valid.
See details
at TEST a MOTOR START or RUN CAPACITOR
More electric motor diagnostic guides and downloads are
at ELECTRIC MOTOR WIRING DIAGRAMS & GUIDES
and in theReferences or Citations section of this article
Typically a centrifugal switch or possibly a PTC or PRD drops the start capacitor from the motor's electrical circuit once the motor has spun up to operating speed, or in some designs, a mechanical centrifugal switch may be used to disconnect the starting capacitor when the motor speed has reached a critical rpm, typically about half of the motor's run speed.[2]
If your electric motor uses a centrifugal switch to cut out the "start" capacitor once the motor is up to speed, a failure of that switch can cause motor failure.
Diagnostic details for a centrifugal switch used on electric motors are
at ELECTRIC MOTOR CENTRIFUGAL SWITCH or PTC PRD
If your electric motor is an "open" design you can see into the motor housing; look for clots of dust and oil that may be blocking the cooling fan and causing the motor to overheat; overheating can cause the motor's thermal overload switch to shut the motor off (and the switch may pop out waiting to cool-down and re-set).
See details
at ELECTRIC MOTOR OVERLOAD RESET
Excerpting from Andy Page, The BASICS of MOTOR CIRCUIT ANALYSIS [PDF] Reliable Plant, (Noria Corporation), 1328 E. 43rd Court, Tulsa, OK 74105
Tel: 800-597-5460; Email: pagea@alliedreliability.com, retrieved 9/13/12, original source: http://www.reliableplant.com/Read/10686/motor-circuit-analysis, Excerpt:
MCA online [tests performed while the motor is operating] can be further split into two categories - current analysis and voltage analysis.
Current analysis is primarily focused on the rotating components. Loose or broken rotor bars, cracked end rings, rotor eccentricity, misalignment and coupling/belt problems are some of the "big-hitter" failure modes detected in the current signature.
Power quality issues like harmful harmonics, voltage imbalances and under/over-voltages are among the issues identified with voltage analysis.
MCA offline is most famous for the resistance-to-ground measurement. But other measurements make motor circuit defects easy to find.
Measuring electrical characteristics like impedance, inductance and capacitance tell the analyst plenty about the condition of the windings.
Inductance is a great indicator of turn-to-turn shorts. Capacitance to ground measures the amount of winding contamination (water, dirt, dust, etc.).
Changes in each of these affect impedance (total resistance of an AC circuit). These characteristics are measured phase to phase and phase to ground and compared to each other and to percent change from baseline to identify motor circuit defects.
Motor circuit analysis (MCA) is often and easily confused with motor current analysis (MCA), which is an abbreviated version of motor current signature analysis (MCSA).
Now moved to ELECTRIC MOTOR 3-PHASE TROUBLESHOOTING
On 2019-02-19 by (mod) - Repeated failures of Trane blower motor
I agree with you that the behavior sounds abnormal. There might be something in the local environment such as unusual moisture or even corrosive gases, or low voltage, or some other installation issue that could be a factor.
Certainly plenty of blower motors run in daily use for decades. Let's both do some research on electric motor failure rates as a function of climate such as Florida. And let's both report back here
On 2019-02-19 by Moshe - 3 ton Trane Package Unit Blower Motor Replaced Twice in 3 Years
I had a 3 ton Trane Package unit installed less than 3 years ago from a reputable company in Miami, FL. In less than 3 years, my blower motor had to be replaced twice. To me, that sounds crazy and like something is just not right either with the unit or the install
Company says its due to humidity / environmental conditions etc. I live in Miami my whole life, never remember any other AC units needing a new blower motor yearly. Is this normal behavior for a practically new AC?
This Q&A were posted originally
at BLOWER FAN OPERATION & TESTING
Watch out: if you are not trained in proper, safe electrical work, stay out of your electric motor - you could be shocked or killed.
Table A: 14 Things to Check (in this order) if an A/C Electric Motor Will Not Start is now found
at ELECTRIC MOTOR WON'T START / RUN - 14 Things to Check
Table B: 7 Things to Check if an Electric Motor Starts but Overheats and Trips its Reset Button or Runs at Abnormal Voltage or Current Levels is now found
Table of Air Conditioning or Heating System Electric Motor Troubleshooting Procedures for a Motor that is Noisy
For document loading speed we moved this data.
Please see separate article: ELECTRIC MOTOR NOISE DIAGNOSIS
Details for this topic have moved to ELECTRIC MOTOR RUN DIRECTION.
In short: check the motor label: uni-directional electric motors run just one way: clockwise (CW) or counterclockwise (CCW) but not both. Bi-directional & self-reversing electric motors run in either direction, CW or CCW. Some electric motors can start and run "backwards" following damage to the motor's start capacitor or windings.
...
Below you will find questions and answers previously posted on this page at its page bottom reader comment box.
On 2022-07-28 by InspectApedia-911 (mod) - motor is drawing too much current
@Tim,
Odd indeed.
Usually high current draw says a motor is having trouble starting, often because of a failing bearing or an excessive load.
But your high current draw is when there is a load. Could the load be tweaking the bearing at the motor's drive shaft?
Other guesses: there could be a failing bearing OR a winding that opens.
On 2022-07-28 by Tim
Hey, I have a 9v dc motor with brushes. It is behaving weirdly. When I hook it up with no load to a power supply and start it, it draws about twice as much current as it should (0.6-0.7A). It also sounds bad. When I hit it with my hand, the current goes back down to the normal range and it gets quieter. It does not do this behavior when it is under load.
What's going on? The commutator looks clean and the brushes aren't worn out so I don't think carbon buildup is an issue. Thanks.
On 2022-07-24 by InspectApedia-911 (mod) - test the windings
@Ernie,
Have you actually tested the windings?
On 2022-07-24 by Ernie
I have a Delta 10" table saw motor that does not work. I have pulled the motor apart: brushes are solid, the commutator is good, the windings appear to be intact, the electrical connections are good. This motor does not have a capacitor that I can find. Off the saw, the motor being plugged in does nothing. Can you suggest anything or is this motor no good.
On 2022-05-23 by InspectApedia-911 (mod)
@Dwight,
Yes that's right
On 2022-05-23 by Dwight
a capicator 250vac at 10 micro farad blow a ahole in the side I order a new onne and there is no polarity on it. it has two black leads comming from it and no polarity markings. can this be installed disconcering the polarity ?
On 2022-04-01 by Inspectapedia Com Moderator - Check the voltage supply to the motor
@David Kruzona,
Check the voltage supply to the motor and check the current draw or amps.
On 2022-04-01 by David Kruzona
I just installed a brand new 1/2 hp 1725 rpm exhaust fan motor. For some unknow reason, it doesn't seem to be running at full speed. The capacitor is brand new on the motor, the wiring is perfect, the fan, bearings pulley, and belt are all new and running smoothly.
Just don't know why it isn't running as fast or strong as the same 1/2 hp motor we pulled out? Thanks for any suggestions...
On 2021-12-13 by Inspectapedia Com Moderator - how to diagnose an electric motor such as a well pump
@Dan,
Take a look at ELECTRIC MOTOR DIAGNOSTIC GUIDE
and keep in mind that if you're not trained in safe electrical work and testing you could be shocked or killed - just sayin'
Or you could take the pump out and ask for its motor to be tested by a local electrical motor repair company who provides that service - compare the estimate of that testing with simply replacing the pump.
Watch out: When a motor is blowing a breaker, and provided it was wired and given the proper amperage to start with, I would never simply try a higher-amp circuit. Doing so invites an electrical fire or injury.
- stay safe
Daniel
On 2021-12-12 by Dan
@Inspectapedia Com Moderator,
I see. I appreciate your insight on this. My understanding is we're at 'the motor needs to be replaced'? Is it worth trying giving it a higher amp circuit?
If the well is toast, I think the shortest path to getting water to this house is connect to municipal water rather than repair the well, but if there's something I can do with just the electrical end of this to get it going, that'd be ideal.
Is that a fair assessment? Is there anything else to give a try before declaring this thing shot?
On 2021-12-12 by Inspectapedia Com Moderator - low resistance and developing short in the pump motor run winding or main winding.
@Dan,
That sounds like you might have a low resistance and developing short in the motor run winding or main winding.
Keep in mind that when the motor starts to spin conditions in the windings can change and a break can open up or short circuit can close.
As a point of comparison, a dead short will show zero or close to zero resistance.
Another test point is measuring the current strong when the motor is attempting to start. For example, if a motor's bearing has seized, the motor will draw High Current
On 2021-12-12 by Dan
@Inspectapedia Com Moderator,
I did test the winding resistances and compared to the chart. The sticker on the motor says 'Model 2801054915' HP 1/2, volts 230
The chart in the box for 1/2 hp 230 volts says "Main BLK-YEL - 4.2-5.2 Ohms" My ohm meter says 1.3 ohms for this. It also says "Start RED-YEL - 15.5-19.6 Ohms"
my meter says 13.3 for this, so both are low, that first one could be a lot too low. It also says the current motor running loaded amps is 5.9 (not sure that's useful)
What do you make of those numbers?
On 2021-12-12 by Inspectapedia Com Moderator - breaker trips immediately when pump is turned on
@Dan,
Do you think we've simply got a dead short - in the pump motor or pump wiring?
Have you tried disconnecting from power (first turn power off) and then checking the resistance between the leads to the pump?
On 2021-12-11 by Dan
[Ed. note: this question, photo, and our reply was first posted at WELL PUMP WIRING REPAIR FAQS]
Alright, let me lay it out:
3 years ago the water was shut off with a water valve. Well pump was replaced in 1996. The well pump motor circuit was left on, but presumably no pumping was required, as no water was being used. I'm now trying to troubleshoot the system.
It's a two phase motor. When I first looked at it, one of the two 120 volt circuits had its breaker tripped, the other didn't. at the regulator, you could see 120 V. If I pushed in the other breaker, the first would immediately trip.
If I open up the box containing the wiring for the pump and the starting capacitor, I could get both breakers pushed in. If I then close the wiring box, I get a spark and the breaker blows.
Suspecting a short, I tested the winding resistances on the motor, and get non zero values across. Not exactly what's on the chart inside the box, but not far off.
Looking at the starting capacitor, it looks like there's a hole in it on the bottom where fluid leaked out, so I replaced it with a smaller one with the same microfarads (59-71). this doesn't change anything. In fact, even with the capacitor not in the system, the breaker flips as soon as the circuit is connected (I suspect if I understood the circuit better this would not be a meaningful statement, but I'll say it here anyway because I'm fuzzy on it).
At the regulator, I see 120 volts to ground on all the leads with both breakers connected. With one breaker pressed, one of the leads says 29 to ground rather than 0, which I found confusing. shouldn't it have said 0?
I'm a little bit lost on how to proceed, I have a couple ideas:
1. the breaker trips immediately when connected. perhaps I need to somehow connect the capacitor to the circuit before the motor starts for it to charge, so the initial current draw doesn't flip the breaker?
Is there some procedure I've missed for replacing the capacitor that does this? or does a 59-71 uF capacitor not have a real charging time? Perhaps having the capacitor blown also can break the blue circuit assembly thing for the capacitor in the circuit box and I need to replace that?
2. I know this idea is probably stupid. the breakers used are 2 independent 20 amp breakers. I could use a different circuit to test using a combined 40 or combined 60 amp breaker instead. maybe it needs a little more current, but is not actually shorted?
Appreciate any insight you guys might have.
Thanks,
Dan
On 2021-11-09 by Inspectapedia Com Moderator - adjustable speed electric hand tool loses power
@GLS Brian,
I don't know.
But it's possible that there is a winding that's opening when the motor tries to speed up or you simply have a defective switch or switch wiring.
I've also seen old Motors that would run at low speed but not at high speed because of a bad bearing
On 2021-11-09 by GLS Brian
I have an adjustable speed electric hand tool that loses power when I increase the speed via the control. Replaced control. no affect.
What would cause the speed loss.?
On 2021-09-19 by danjoefriedman (mod) - motor might have been damaged
@Owen Kigula,
You can try and stalling a hard start capacitor kit but I'm not optimistic as it sounds as if your motor has been damaged.
On 2021-09-19 by Owen Kigula
My motor has a hard start and it was due to a high voltage wat can I do
On 2021-08-24 by inspectapedia.com.moderator
Re-posting without advertising link:
Levi Armstrong · 35 minutes ago
It's great that you mentioned that when buying replacement electric motors, fuel units, and blower fan assemblies to be sure they all are compatible. My brother will repair his electric motor to get his boat up and running again. I'll share this with him since he is still familiarizing himself with fixing it. Thanks!
Moderator reply:
Your link won't post but if you provide even the smallest technical content contribution to InspectApedia.com such as suggested corrections to an article or new content or photos or suggestions, that does give a legitimate opportunity for us to include your website link and contact information.
Contributing content, criticism, corrections, photo images are great ways to receive a referral link from InspectAPedia.com at no cost, and we all benefit from the increased accuracy and content. Content contributors to InspectApedia.com can also provide their link information using the form at InspectAPedia.com - Directory Listing & Link Exchange Instructions found at https://inspectapedia.com/Link_Exchange.htm
On 2021-07-17 by inspectapedia.com.moderator
@Bob R,
If you install the proper capacitor - correct size and specs - and wire it properly, and IF the capacitor was all that's needed, then turning on power to the motor will charge the capacitor and start the motor. You don't have to give it a spin.
If that doesn't work then there's another problem with wiring or with the motor itself.
Watch out: if you are not familiar with proper and safe electrical wiring you could be shocked or killed .
On 2021-07-17 by Bob R
I have purchased 2 capacitors for a 5 hp 220 v motor that hums. I assume they do not come charged. How do I do it? Spin the motor?
On 2021-05-12 by (mod) - motor hums on start-up
@noah,
It could be that the motor or a bearing in the motor is failing but a reasonable check that most service techs would make is to
simply swap in a new start capacitor. That may give you some more life out of the motor.
On 2021-05-08 by noah
I have a two speed electric motor for my wife's Spa/Hot tub, but it only has a single start capacitor. The issue is that the motor will start properly when power is applied to the high speed terminal, but won't start (just 'hums') when power is applied to the low speed terminal.
If I get the motor started with the high speed terminal and then switch power to low speed winding, it will continue to run just fine, but it won't start up on that winding. It used to start up on either winding. What is the issue? I thought that if the capacitor was bad, it wouldn't start on either setting, but starts fine on one but not the other.
On 2021-05-02 by (mod) - on-off cycling 12V motor
@Peter Tozer,
I would look for a loose electrical connection,
an excessive load being applied to the motor,
A bad bearing,
For if the motor is being controlled by a relay, a bad relay
On 2021-05-02 by Peter Tozer
I have a 12 volt electrical motor which goes start/stop/start/stop and so on in very rapid succession when connected to the battery. what is wrong with it?
On 2021-04-13 by (mod) - causes of motor loss of torque and increased current draw
@Chjris,
Most-often the motor problem you describe, loss of torque and increased current draw (until it trips the circuit breaker) is caused by
1. overloading of the motor: for example if the compressor itself whose piston and other moving parts is failing due to wear or poor lubrication or a bad bearing, or due to backpressure load on the compressor, then the electric motor driving the compressor will face an abnormally high load that in turn can cause the motor to overheat or draw excessive current. Ultimately the compressor itself may seize or the motor driving it may seize.
2. failing bearings in the electric motor itself, again causing a resistance to turning or moving parts that leads to overheating of the motor itself, higher current draw, until the motor trips the circuit breaker; ultimately the motor itself may seize.
On 2021-04-13 by Chjris
I have 2hp motor that will start. However, the longer it runs the less torque it has. then it will pop the breaker, It goes on a compressor.
On 2021-03-21 - by (mod) -
@Dennis E Strawn, reset of a tripped motor safety switch can require some time to allow the motor and overheat sensor to cool down.
And yes, low voltage can prevent a motor from running or starting and might result in a humming motor.
On 2021-03-20 by Dennis E Strawn
Have an air compressue motor that will hum for a few seconds before stopp[ng. Has a reset button on motor, but doesnt seem to reset. Have a voltage supply of 123 volts now, but before I corrected the recepticle connection, it wasnt getting the 120 volts that it needed.
On 2021-02-24 - by (mod) -
@Anonymous, in the recommended reading list found at the end of the article above you will want to click on the link to the article titled
CAPACITORS for HARD STARTING MOTORS
0 you will also see in the article index or near the end of the article I just recommended other links to procedure for selecting the correct capacitor
On 2021-02-24 by Anonymous
I need help with choosing the right capacitor could you help me please my email istalal 6611 9116 Gmail
On 2021-01-02 - by (mod) -
Luis
If by undulating you are describing a motor whose speed seems to keep speeding up then slowing down,
I would first check the stability of the supply voltage to the motor.
Other possibilities are a failing bearing, overheating, a poor electrical connection, or a winding that opens when the motor gets up to higher speed.
On 2021-01-02 by Luis Martinez
What is the cause of motor undulating?
...
Continue reading at ELECTRIC MOTOR OVERLOAD RESET or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.
Or see ELECTRIC MOTOR DIAGNOSTIC FAQs - questions & answers posted originally at this page.
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ELECTRIC MOTOR DIAGNOSTIC GUIDE at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.
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