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Photograph of the overload reset button on an electric motor Electric Motor Reset Button FAQs
Q&A on Thermal Overload Switch on Electric motors

Electric motor thermal overload switch FAQs:

Frequently asked questions about the thermal overload and reset button on electric motors.

This article series describes how to find and reset the thermal overload button on an electric motor and we give suggestions for repairing hard-starting or non-starting electric motors such as on air conditioning condenser fans and blower fans.

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Electric Motor Reset Button & Thermal Overload Questions & Answers

Photograph of the overload reset button on an electric motor

Questions & answers about the reset button or reset feature on electric motors, posted originally at ELECTRIC MOTOR OVERLOAD RESET - topic home page.

Also see ELECTRIC MOTOR DIAGNOSTIC GUIDE

Question: where to obtain safe internal operating temperature for an A-insulated 1952 elecgric Singer Sewing Machine Motor?

Im am rewiring a 1953 Singer Featherweight 222K with original 220 volts motor. I plan installing some small thermostatic circuit breakers to protect the motor, the foot switch and machine arm (with the wiring for the Singerlight lamp) from owerheating.

I will use silicone-insulated cables standing uo to 200 C heat, so the first component to be damaged from exess heat is the motor windings, insulated by dipping in with shellac insulating varnish, which was the standard industry procedure in 1953.

If one chooses breakers with a too low trip value they will stop the machine at normal operating temperatures, if one chooses breakers with too high trip value, the insulation could burn.

Now, what would be a suitable trigger temperature for those circuit brakers, or in other words,
what is your informed oppinion on the maximum recomendable and safe internal operation temperature for a A-insulated electrical motor from 1952 in original condition? - Gunnar Pettersson, Finland 3/10/2014

Reply:

G.P. Thank you for an interesting question; with regrets, I do not have an answer immediately at hand. I'm a bit nervous about citing a specific "safe temperature" for a 1952 electric motor as I suspect that there was a range of acceptable temperatures based on motor design and application.

I can suggest some references that might help narrow the question to help a bit, for which Farrell's article might be most helpful.

Reader followp-up:

... this question seems to be difficult to find an answer to on the web. I am very far from beeing an electricien (or how one puts in English) but I understand here are two things in play: the normal calculations and safety margins for a modern motor with modern materials, and then the older designs, using older materials and thereupon the ageing factor of those old time materials. Kind of industrial archeology.

In my basement I have a thick book, I think it is Swedish, but it may be in Finnish, named "Electricity".

I have it after my uncle whom I never saw, as he was killed as a young officer in the war, I think it was 1941. He was a quite promising electrical engineer, and he wrote nice and clear formulas in his workbooks, where I write as we say crow's feet. He must have had a good mathematical sensem where I am almost illiterate.

Among his books was one with the title "Introduction to higher analysis" (in Finnish) by Ernest Lindelöf:
http://en.wikipedia.org/wiki/Ernst_Leonard_Lindel%C3%B6f

Some professor in mathematics heard that my sister, professor H. had this book and begged for the favor to keep it for some time. It was well before the internet era.

So, still we do not now, what the temperature limit inside a Singer external, pre-1960 motor for home sewing machines model NN should be.

We do, however know, what solder one should use in the rewiring: "“63-37” means it’s 63% tin and 37% lead.

This specific percentage is what Singer 221 guru Graham Forsdyke’s motor specialist uses, and he used to work in the Singer factory in Kilbowie, so I’m sure he knows his stuff."

I am sure the information on "aged shellac safe" internal motor temperature can be found in the books you name, maybe as a tabel, or formula in them. Or maybe I find it in "Elektricity". I read the book in my childhood and remeber it beeing full of illustrations of vintage applications.

But as it was a brave new world and the technology of tomorrow for the writer, they probably were not observant of the problematics concerning ageing of insulation materials.

On 2015-02-22 by (mod) - While changing motor on boiler. One wire going to transformer came loose where do I connect it to?

Pete,

Typicallly an oil burner ignition transformer, labelled "ignition" on wiring charts, has just 2 black wires, connected by twist on connector to,the same terminals or wires as the burner motor ...

you will want to check the wiring diagram for the particular control your oil burner is using. Here's an example...

On a typical protectorelay wiring the transformer is wired in parallel with the oil burner motor and with the oil valve if one is used.

There one side of those devices connects to the orange wire of the protectorelay and the other connects to L2 the white wire.

Your setup, of which we know nothing, may vary so take a look at the installation guide for your controls.

On 2015-02-22 by Pete

While changing motor on boiler. One wire going to transformer came loose where do I connect it to?

On 2015-02-21 by (mod) - signs of a bad motor bearing

Bg.

Typically a failing bearing that's binding, or a failing start mechanism will trip the motor overload button.

But we need to diagnose the trouble a bit before buying a new motor. For example, if the blower fan bearing, coupling, or an oil pump unit has a failing bearing or is binding, both of which are driven by the burner motor, can cause the motor to overload and trip. If one of those is the problem, having a spare motor is the wrong "fix"

On 2015-02-19 by bgroobs48

Last night the heat in my house went down. I found the motor on my beckett afg burner was in thermal overload. I reset the motor and restarted the boiler.

It has been running fine now for the last 12 hours. My question is could this have been a fluke, or should I replace the motor rather than risk losing heat and perhaps causing the pipes to freeze during this arctic weather we are having?


On 2015-02-05 by (mod) - rapid clicking noise, source unclear

I'd call my local heating service tech: I'm not clear if this noise is in a control - such as a failing relay - or something else.

The fact that the problem goes away by adjusting the thermostat - thermosatat on the water heater - is suggesting a failing control but I'd look first for a loose wire.

On 2015-02-04 by Laine

I have hot water heating - boiler system - in my home. Occasionally, and always in the wee hours of the morning, I hear a rapid clicking noise coming from the boiler which I think may be a starter or sorts. It goes away if I adjust the thermostat slightly.

I have looked around to find out if there is a "starter" [not the electrical switch] that causes the heat exchanger or boiler to engage but I have not found anything useful at this point. Any thoughts on what this sound may be?

Thanks.

On 2014-11-07 by (mod) - check the motor capacitor

Dale I'd start by checking the start/run capacitor

Also look closely at the fan relay

On 2014-11-07 by Dale Morehouse

My outdooor unit fan starts but trips back out again before it ramps up. it keeps trying for about 8 times then trips out.

It was working fine this spring when I stopped using it for the summer. It is a 3 ton Keeprite with the indoor unit on a Lennox gas furnace. It is about 3 years old.

On 2014-07-28 by (mod) - turn off the squealing air conditioning syste

Lisette,
Yes I would turn off the squealing air conditioning system

See

https://inspectapedia.com/aircond/HVAC_Noise_Descriptions_5.htm

For information about the squealing AC sound you described.m

On 2014-07-28 by LISETTE PADIILLA-DIAMOND

My outdoord AC is having a high pitch squealing sound... The cold air is still coming out in my house thru the vents, but should i turn the ac off due to the high squealing coming from the ac outside?

On 2014-07-08 by (mod) - bad replacement part -

Sometimes we just have the bad luck of striking into a bad replacement part - or a series of them all made in the same batch. But I'd also look at why the motor is failing - as you suggest. Check the motor temperature against its ratings, check the voltage levels for low voltage, and of course for fan motors check other moving parts for binding.

And yes a motor widing can open when the motor is spinning.

On 2014-07-08 19:34:46.800740 by Derek

i have had my capacitor bad before but replaced the motor first thinking it was the problem then found out my run capacitor was blown 3 years ago. i put the same exact motor new on it. this year its acting the same way and the capacitor was blown and i replaced. the ac runs for a while and longer on cooler days

but eventually the fan motor stops spinning and the compressor is still working. is the motor just geting hot, or could it be high pressure switch or something else causing this? im sure whatever the case its what caused the capacitor to blow last time

but im not sure since i had changed the motor first 3 years ago and then capacitor when fan wouldnt spin. could the motor geting hot cause the capacitor to go bad and can something be causing the motor itself to get hot and turn off or the windings? when its spinning its spinning fast and smooth sounding!!

On 2014-06-09 by xenaon

i rent from a bad guy. He shut off the wall switch - which shut off the fan. Before, if I turned on the wall switch - the AC went on. Now, it doesn't. Inside my apt the AC and Furnace breakers are fine. 3 hours later, the bully shut off the gas water tank downstairs - turning the switch horizontal, then setting it to off and vacation, so the pilot light is out.

I cannot relight the pilot - turn on the gas line, hold down the pilot valve - won't light.

I cannot find a way to turn on the Rheem Criterian II gas/AC unit. What else needs to be turned on? Thermostat (Honeywell) does not ignite the AC or fan or heat - but it could not possibly be the thermostat as the person who shut off the fan switch - also turned off the water heater.

On 2014-03-10 by (mod) - reset button needing reset

Anon, search InspectApedia for FAN LIMIT switch to understand your question and our reply in a more relevant context:

No Anon. In a properly wired forced warm air heating system in usual operation the blower stays off until the supply plenum has reached the FAN ON temperature. This is to avoid blowing cold air on building occupants.

On many systems it's possible to override this arrangement by setting a thermostat or limit switch fan ON in Manual mode. In that case the fan would run continuously regardless of thermostat setting - not the case you describe.

On 2014-03-01 by Anonymous

fortunately my problem lied with the reset button needing reset. However, as I had been away for a good chunk of the day, by the time I got home it was mighty chilly in side.

This happened because although the burner was not turning on, the blower kept at it, bringing more and more cold air from crawl space/basement into the house. SO my Q: will blower always turn on if thermostat calls for heat, even without burner starting up first?

On 2012-11-14 by Sheena

My heating and cooling unit is acting up. The last to mornings I woke up to no heat.

The first day we replaced the capacitor with one we had on hand(because it had acted up during the summer and my husband had an extra). It worked for a few hours into the night and then nothing again.

Replaced the capacitor again today on advisement of a HVAC guy thinking maybe we'd had it so long it had gone bad?

Again, this evening and a few hours later, we are without heat... Any ideas on what our next parts and steps may be?

On 2012-09-06 by (mod) -

John,

thanks for the interesting question about a hot saw motor; Indeed I've taken electric motors to a repair shop for salvation or rebuilding - an approach that can cost less than buying a new motor;

But before taking that step, I'd look carefully at the whole saw assembly to see if I could find something that's binding. Does the motor spin freely when power is off? Is a saw brake partly engaged? Is the voltage abnormally low on your saw circut?

On 2012-09-04 by John

I recently began using my radial arm saw again after a 10 year absence and the motor keeps shotting down after only a brief run.

Once it cools I can push the rest button and it will start again but only run for a short period. Assuming that the rest system has failed to operate properly can I take the motor in to an electrical service shop and have them repair or replace it?

On 2012-09-04 by Jonathan

My condenser works just fine, but the blower fan will not work properly in Auto--we have been running it (for a few weeks) full-time, but sometimes it kicks off and does not run at all while the condenser still runs.

Flipping the power switch to the furnace unit off/on will restart the fan just fine for a few days before it kicks off again. Also, I don't think that it is moving as much air as it used to. My diagnosis: I need a new blower fan motor. Is this correct?

On 2012-08-20 by Fan in central A/C outdoor compr

Inside our home, the A/C blows air but it is not cooling. I checked the compressor outside and there was the usaul 'humming noise' but the fan was not running. 3 weeks ago, it was not not cooling the house to desired temp. and the fan was going off and on evry minute or two.

Turned it off overnight, next mournig it appeared to be working. A/C tech came and also sucked water out of the PVC pipe near the condensor

It was working again but now, 3 weeks later, it is not cooling the house at all. I sucked water out, turned it off overnight but it is not cooling the house and all and the fan is not rotating.

Before turning it off at night I noticed the metal cover around it was warm to the touch. Recently, they removed the shrubs near the condenssor that provided some shade. Could this have led to the full sun over-heating the compressor? What can I do or what should I expect the AC tech to do?

On 2012-08-06 by (mod) -

Kim, that's a relief. In that case it sounds as if either there is a shorted wire or the motor is binding up and drawing high current at start-up.

There is a chance that the service tech can get the motor running for a while longer by installing a hard-start capacitor on the motor - but it sounds as if the motor is going to need replacement.

On 2012-08-06 by Kim

Hi Dan. Sorry! I didnot make it clear. It is the individual circuit breaker tripping. The breaker that assign to the furnace/Ac unit only. Thank.

On 2012-08-05 by (mod) -

Kim,

An unsafe electrical circuit or bad breaker is certainly part of your problem - you should shut down the system and call a licensed electrician.

I infer this because you say that the MAIN breaker is tripping off - which means that within the electrical panel you have an overcurrent on the blower circuit but that individual circuit breaker is NOT TRIPPING - a dangerous condition asking for a fire.

So even if the root problem is a bad blower motor, a hard starting motor, a bad atart/run capacitor, or a seized motor, the fact that the individual circuit breaker doesn't trip means bigger trouble.

On 2012-08-05 by Kim

My blower unit keep tripping off the main circuit breaker power switch. After resetting the circuit, the unit works fine. It happens more frequent now. What is the probable cause?

On 2012-07-19 by (mod) -

Larry I see by your noting on this particular page that we're on the same track - if the blower doesn't run indeed the coil can ice over. The fact that the fan runs on manual makes it sound as if there is a control switch or relay problem, maybe even a bad wiring connection.

I'd spend some time tracking down that wiring and control in the air handler.

On 2012-07-19 by Larry

my air conditioner will run fine until it kicks off after it cools the house to the temp setting.

The fan will not kick on so it freezes up. You can let it unthaw and put fan on manuel and it works fine for days until you put fan back to auto. Have changed thermostat, switch and compasitor but will still freeze up on auto, also checked freon no leaks.

On 2012-07-12 by vjm


FIXED!!! stuck limit switch on the furnace door.

On 2012-07-12 by vjm

Outside Carrier condenser unit working fine. Fan blades running. Normal sounds. No cool air in the house because the blower fan located in the (Payne) furnace compartment will not turn on. Won't go on either with "fan auto" setting or with "fan on" setting. Triple digits today! TIA

On 2012-07-11 by Cindi

Our Carrier unit is only 5 yrs old. Outside unit motor running but the fan blades are not turning. Some cool air is blowing out but not much. Inside fan working. Could this be a bad fan motor. Really not wanting to have to buy another unit.

On 2012-06-19 by (mod) -

John you are writing about thermostat wiring on a page about electric motor resets. You might want to check out the diagnostic articles found under THERMOSTATS, HEATING / COOLING - link at page bottom ARTICLE INDEX .

If you shorted a wire you could have damaged the thermostat, its transformer, or another component.

On 2012-06-19 by john

outside thermostat cut by mistake...spliced back together and reset all fuze switched involved, yet ac will no longer come on??

On 2012-06-18 by (mod) -

Not sure, Ron; could be normal in some weather, or could be a bad relay or control board.

On 2012-06-16 by RON LOYCHE

The unit does cool down the house but then the outside fan doesn't shut off after an extended time

On 2012-05-30 by (mod) -

Tom,

If the indoor blower unit runs but the outside compressor / condenser unit does not, you'll have air movement but no cooling. In the links above see the LOST COOLING CAPACITY link, or at our air conditioning page you can use the diagnostic procedures at
COMPRESSOR & CONDENSING COIL, A/C

On 2012-05-30 by (mod) -

Bill, if a compressor is overheating it could be due to a failing motor, internal motor damage, or even a bad start/run capacitor

On 2012-05-30 by tom

turned our central air on and the fan is running but very very little cool air is coming out of vents. the motor doesnt seem to be hot at all its like the compressor isnt kicking on.. what do i check or do?

On 2012-05-29 by bill

a brand new ac unit installed last fall keeps shutting down after about 10 minuts seems to be the compressor overheating as after an hour or so it will restart and run untll it overheats again all other components seem to run normally what would cause the compressor to keep overheating

On 2011-10-21 by (mod) -

Adelita & Bernardino,

If you make sure that the thermostat is calling for cooling, that the power switches are all "ON" to your equipment, and if the A/C still is not working, with all due respect, I see from the question that you would be best served by calling an HVAC repair company.

It would be too wild speculation for me to guess about your system when I have absolutely no information about the system or the problem other than just your note.

On 2011-10-19 by Adelita R. & Bernardino Del Ange

Why my A/C doesn't work at all? You don't hear the motor working at all. Can you give me a answer what is the problem with my A/C? We don't want to mess with it. Where is the "reset" button at?

On 2011-09-01 by (mod) -

Dave it's possible that icing in the HVAC system could cause refrigerant to return to the compressor in liquid form, damaging the compressor motor itself. Your HVAC tech should check out the condition of the compressor, and its start/run capacitor first. You won't find a manual reset button on most condenser compressor motors though some fan motors may have one.

On 2011-08-29 by Dave

Our tenant says they had blocked several vents, and the pipes started to frost up. now, after a month of not using the unit, the conderser fan unit won't start, but the blower will run when the thermostat is turned to "on". All circuit breakers are on. Is it possibly a "reset" on the condenser motor? Any ideas??

On 2011-08-11 by (mod) -

If your A/C system stops working when it's very hot outside it sounds as if one of the motors, most often the compressor but sometimes a fan motor, is overheating and going off on thermal reset.

On 2011-08-10 by hossein saffar

why my airconditioning unit stops cooling after severl hours working when outside tempeture get high? thanks

On 2011-08-09 by (mod) -

LaRhonda and Ram, you'll want to look at our A/C diagnostic advice beginning in the article LOST COOLING CAPACITY (links at page bottom ARTICLE INDEX ).

If your inside air handler is "running" but no air is coming out of vents, you may have a blower fan that has come disconnected (such as a broken drive belt on pulley-driven units) or a cooling coil that has iced over and is blocking airflow.

On 2011-08-09 by Ram

Hi
I have exactly similar situation. The inside unit is running but I don't get any air from the vents. It was working yesterday. I checked the outside unit and see that fan is not running. I changed the fuses without any success. Is the motor inside? Do I have to open the unit. It is big unit. This is Airtemp central AC system. Now my whole house is warm. Inside temp. 82 degree.

On 2011-08-09 by LaRhonda

Hello My inside ac unit is running but not putting out cold air, outside compressor unit is not running and is hot to touch. Breakers are all on and switches are all on. Please help, we are sooo hot! Thanks

On 2011-08-08 by (mod) -

Steve your description of getting the condenser fan running by spinning it with a screwdriver is a good indication that you need a new start/run capacitor for the fan motor.

Take a look at the article linked-to at page bottom ARTICLE INDEX , titled: CAPACITORS for HARD STARTING MOTORS

On 2011-08-07 by steve

The condensers fan motor will start but the fan will not turn. I push the blade with an object "Screwdriver" and it will begin moving and working fine. Later If the moter dosen't turn on I hit the orange reset switch outside the unit and push the blade again. Any ideas???

On 2011-08-01 by (mod) -

Chris your helpful feedback is a reminder that when an electric motor is not starting or is buzzing the problem may be the start/run capacitor and not a thermal overload reset switch.

On 2011-08-01 by chris

Never mind, it was the capacitor, replaced that and back up and running fine.

On 2011-07-31 by chris

Having an issue where all I am getting from the inside unit is a buzzing sound. The blower motor was very hot, but I can't find a reset button on it either. The filter was pretty dirty. Would it be a scenerio where it could be a bad motor or capacitor? The unit is a Lennox. Any help is greatly appreciated.

On 2011-07-30 by (mod) -

John: in the case you describe, your compressor may need a hard-start capacitor kit (search our website for "hard start capacitor kit" to read about these if your fuse blows again.

On 2011-07-30 by John

The fan would run but the conpressor would not run at all. I checked the fuse outside and replace them being that I had been in the house for over 7 years.I like to start low when it comes to cost. 2 fuse cost me 12$.Hope this can help another.

On 2011-06-07 by Ron

I'm looking to find what would cause a central air conditioner condenser to run continuously.

The fan that sucks air over the tubing from the condenser shuts on and off, the the fan that circulates the air inside the building turns off, but the condenser keeps running. Can anyone help? Thank you.


...

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