Recent Electric motor thermal overload switch diagnostic FAQs set #2

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.

Electric Motor Reset Button & Thermal Overload Questions & Answers

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

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Can a bad electric motor overload switch cause the circuit breaker to trip?

Have an AO Smith motor new start/run caps centrifugal switch is good windings are good; the only part left is the thermal limit switch.

Can this part cause house circuit breaker to trip on startup it trys to start 3 seconds or less circuit breaker trips and motor fails to start. On 2018-05-09 by JJ

Normally I wouldn't think so JJ, though it's possible that a motor is drawing high current or overheating and not tripping its local reset button; in that case yes it might draw enough current to trip the circuit breaker.

From just your text (and without any electric motor test results) It does sound as if the motor is drawing high amps and tripping the breaker.

Keep in mind that a bench test of windings can be misleading - windings can move, open, or short when the motor gets up to speed. I'd put a clamp-on ammeter on the circuit and watch closely for a spike after 3 seconds.

The thermal limit switch in an electric motor monitors winding temperature and is designed to go from normally closed (NC) to "open" if the temperature at the winding exceeds the manufacturer's specifications. It's a rather simple device.

Let's test the thermal limit switch itself, out of the motor.

With the ambient temperature and the limit switch temperature under 85 degF, set the VOM to Ohms on the 1x scale.
The switch should be closed (conductive) (very low resistance) until the switch becomes hot.

If the switch has zero resistance it might be shorted. If it has very high resistance it's not working at all. (That wont' be your case).

These switches are typically a "snap action" device: the switch will be either open or closed. Only if a switch terminal or wire were becoming shorted to the motor body or to ground would I suspect the switch as the cause of a circuit breaker trip.

Here is a LIMIT SWITCH TECHNICAL GUIDE [PDF] from Abzil North America https://us.azbil.comhttps://inspectapedia.com/electric/Limit-Switch-Technical-Guide-azbil.com.pdf retrieved 2018/05/09 original source http://us.azbil.com/CP-GC1003E_Vol.1_a_c/D/TEC_LIMIT_SWITCHES.pdf

That document points out a fundamental design criterion: the switch circuit must be configured so that it won't be shorted if the limit switch malfunctions. This ought to be the case for all motor thermal limit switches.

This article from US Motors explains thermal switches on motors in a clear concise page http://acim.nidec.com/motors/usmotors/techdocs/profacts/winding-temp-protection/thermostats

A/C compressor motor keeps overheating - automatically resets after 30 minutes

I have a problem with my compressor motor which keeps overheating. It automatically resets itself after 30 minutes or so. I keep the house at 80 during the day and 77 at night. Any ideas on what I need to do? I live in Boca Raton Florida On 2017-07-17 by Greg

Reply by (mod) - compressor motor is failing

Greg,

I suspect the compressor motor is failing. A service tech can confirm that by current draw measurements.

My dog chewed the A/C wires, now the condenser unit won't turn on

My dog chewed apart the two wires that run from house to ac unit. Twist back together but fan or compressor will not come on. Fuse was blown on control board and replaced but fan or compressor still doesn't works. Can manually press contact's and everything works.

A technician came and fix it in 10 mins in the attic. Now my dog has done it again in one week.

What did the tech do, I have done everything. Is there a reset button somewhere for the fan and compressor inside or outside. This is an old carrier a.c. unit On 2017-07-09 by Ronald

by (mod) - use metal conduit or BX flexible armored cable wiring

Ronald

I can't quite see from my spot what the tech fixed in the air handler: perhaps a fuse or a bad control board relay.

When she comes to fix it again I'd look into protecting the wiring in metal conduit since your dog clearly likes the taste of those wires.

Other animals will chew wire insulation too, such as rats (bad dogs), cats, and squirrels.

A/C unit won't turn on

AC unit is approximately 10 years old. It quit working and will not turn on. I turn the thermostat to “Cool” and all I hear is a click at the outside unit but nothing goes on, neither the fan nor the compressor. Last summer I was hearing the compressor flutter a bit (like it was struggling) so I think that may be the issue.

I’ve checked the voltage and I have 240v coming from the elec panel and into the disconnect near the unit. I also have 240v going out of the disconnect to the contactor. I checked the incoming voltage at the contactor, also 240v (120v between hot/ground, and 120v between 2nd hot/ground). I replaced the capacitor with a new one this spring.

I also replaced the contactor. The fact that I’m hearing a click leads me to believe that the thermostat is initiating the contactor. I haven’t been successful in ensuring I have 24v across the contactor to the capacitor but the fact that I have a brand new contactor makes me think that’s not the issue.

I did try to bump the fan manually when the entire system was on “Cool” – nothing happened. Inside, I’ve got a new filter and I don’t have a clogged condensate line. This leaves only two things, the fan motor and the compressor. How can I test those two to see which one is the problem?

Seems like one of the two should turn on regardless when the thermostat calls to start the cooling, unless they are both bad?

Or is the fan interlocked with the compressor somehow? My understanding is that the call to cool from the thermostat wire initiates 24v across the contactor to send to the capacitor which then fires the fan and the compressor and the voltage demand is transferred to the permanent electrical wires.
Any help is much appreciated. On 2017-06-11 by Ryan

Ryan,

Provided you're comfortable and trained enough to not get killed fooling with the electrical components, (no offense intended I just prefer live readers) you'd check for voltage right at each motor's terminals, and if not present work backwards from that point.

Details and 10 easy diagnostic steps are

at AIR CONDITIONER WON'T START

WATCH OUT: turn power off when accessing equipment and watch out for hazards of death by electrical shock.

 

Water pump won't stop and motor is extremely hot

cut-in an cut-out reach the proper lbs it takes about 20min to reach the cut-out pressure an by then the pump is extremely hot.....can anyone help me out please On 2017-04-13 by spenc

Sure, Spenc.

By using the search box just above to search InspectApedia for PUMP WON'T STOP RUNNING we find

WATER PUMP WONT STOP RUNNING that explains how to diagnose and fix the problem.

It sounds as if your pump is having trouble reaching the cut-off pressure but we don't know if that's because of a low flow well, piping leaks, low voltage to the pump, a damaged pump impeller, etc.

 

Why do I have to push the well pump motor reset button every morning?

My well shuts off at night. I have to hit the reset button every morning then it is OK for the rest of the day. On 2016-01-20 by Dan

by (mod) re: well pump protector may shut down the pump if water is low

If your system has a well protection circuit or control or switch it may be shutting down the pump to prevent a burn-up of a pump running constantly but unable to find enough water to reach the cutoff pressure.

Then when the pump is off the well slowly recovers so that by day time you can turn it on again and reach cutoff pressure again.

I'd look for

- leaky foot valve

-leak in well piping

- slow well recovery rate

- high current draw at the pump indicating a pump motor failure developing

 

 

How do I find the reset button on a Trane 2000 Electric Furnace?

FIND RESET BUTTON ON A 2000 ELECTRIC TRANE FURNACE ? On 2015-12-12 by ANN

by (mod) re: reset button on a Trane electric furnace

Ann:

Trane sells heat pumps, gas furnaces, perhaps heat pumps with electric backup heat.

An electric furnace may trip a circuit breaker if the electric heaters are in trouble. Those'd be in the electrical panel.

There may also be local circuit breakers in the unit controlling the heating elements.

If a blower motor won't run there MIGHT be a re-set button on the motor itself.

Click over to our page TRANE AIR CONDITIONER FURNACE HEAT PUMP MANUALS & PARTS where you can download for free the IO manual for your Trane furnace.

Therein the reset buttons will be shown.

 

Tell me why the internal thermal overload in electric motor turns it off and back on

I repowered a direct drive organ blower from the 1920s with a Baldor airover .5 hp 1100 RPM (same specs as original) and made it a belt drive. The motor shuts off after about an hour, very hot to the touch. The motor does not have a thermal overload switch (Baldor CHC365A) but it will re-start when it cools off.

Question 1: if it doesn't have an overload switch, what is happening?

Question 2: (this is where it gets weird)

The motor is on a switched duplex outlet. I have a small fan plugged into the other receptacle to cool the motor.

When the motor switches off, the small fan also stops (??). AFter five minutes the small fan will come on again, run for a few minutes and then shut off; the motor does not come on until the small fan has started and stopped a few times.

I can only surmise that the circuit in the church has some sort of automatic overload switch?? It does not trip a breaker.
thanks On 2015-08-13 by dave.irland@gmail.com

Reply by (mod) -

The motor may have an internal thermal overload switch that automatically re-sets when the motor cools.

I'm not a motor expert but I'd at least check for

- improper voltage

- improper wiring

- a binding bearing or moving part that is stressing the motor

- missing motor lubrication

- a motor winding that opens up (and stops the motor) when the motor gets hot

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

Or see these

Recommended Articles

• CAPACITORS for HARD STARTING MOTORS for advice on adding or replacing a start/run capacitor for an electric motor that has trouble starting.
• ELECTRIC MOTOR DIAGNOSTIC GUIDE
• ELECTRIC MOTOR WIRING DIAGRAMS & GUIDES

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