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FIXED NS-RTM12SS7-C Insignia-branded Refrigerator, compressor doesn't start

Cubytus

Premium Member
Joined
Nov 28, 2016
Messages
43
Location
A 110VAC country
Model Number
NS-RTM12SS7-C
Age
1-5 years
Hi there,

I have an Insignia fridge model NS-RTM12SS7-C that was in storage for a couple of years (vertically).

Symptoms: When first plugged in, after a few seconds the compressor starts, then turns off. Inside the fridge, the controller alternatively flashes all 5 LEDs on the electronic controller, then the middle one. Listening to the electronic controller, I can hear a faint click (relay) every few seconds.
Putting a hand on the compressor, I can feel it briefly vibrating at the same time the electronic controller inside the fridge is clicking.

My guess: Apparently the controller tries to restart the compressor, to no avail. Both overload fuse and start relay appear to be working, otherwise the compressor wouldn't start at all.

Already tried switching some parts with same parts from identical, known-good unit.
  • electronic controllers. Compressor doesn't start.
  • overload fuse+start relay: seemed to work at first, but quickly failed with same symptoms. Conversely, the OL fuse+start relay assembly from the failed unit triggered the exact same symptoms in the known-good unit.
  • start relay only, replaced the TRIAC inside a I thought this would be the only part likely to break. Compressor doesn't start.
Also replaced the start relay with a band new part, same sequence: short compressor run, turns off, doesn't restart.
Leaving the fridge unplugged for a few hours, then plugging it back in triggers the exact same sequence: a few seconds latency, then about 30 seconds compressor runtime, then clicking relays+flashing LEDs+slight compressor vibration.

Not tried:
hot-wiring the compressor. I thought it would be unnecessary since it would run, albeit for a very short time.
Measuring voltage between common and start, and common / run windings. As I understand it, "common + run" should always show about 120V, and "common + start" should show 120V in the first few seconds, then gradually lowering as the PTC heating up prevents current from flowing.
Measuring current reaching the start and the run windings, respectively.
Measuring windings resistance.
Remarks: the start relay isn't a simple 4.7Ω PTC, but contains a TRIAC, although I'm not sure why. Replacing it with a simple 4.7Ω PTC from another fridge doesn't work.

Unsolved questions: why would the compressor stop in the first place?
And what would be the likely failure cause in this case?
 

Dan O.

Appliance Tech
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why would the compressor stop in the first place?Q

There are 2 possibilies. 1. The control stops sending power to it. 2. The overload is cutting the power out.

The latter could possibly be due to too high of amperage draw, the compressor getting too hot, or the relay and/or overload being defective.

And what would be the likely failure cause in this case?

A defective compressor, a defective relay and/overload protector or a defective electronic control.

If there's still power at the compressor when it stops operating, the problem is at the compressor. The control system would stop power from even getting to the compressor.


the start relay isn't a simple 4.7Ω PTC, but contains a TRIAC,

I've never heard of such a thing. Are you certain you're not referring to a capacitor??


Dan O.
 

Cubytus

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Messages
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Location
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Thanks Dan, I'll try to make it clearer.

Here are the combinations I tried. "Known Good" refers to the, well, working fridge.
"Known Good"FailedCombination #1Combination #2Combination #3Combination #4
KG-CompressorF-CompressorF-CompressorF-CompressorKG-CompressorF-Compressor
KG-ControllerF-ControllerKG-ControllerKG-ControllerF-ControllerKG-Controller
KG-PTCF-start relayF-start relayKG-start relayKG-start relaystart relay (Brand new and repaired)
KG-Overload fuseF-Overload fuseF-Overload fuseF-Overload fuseKG-Overload fuseF-Overload fuse
WORKSDOESN'T WORKDOESN'T WORKWORKSWORKSDOESN'T WORK

Of course I didn't keep Combination #2 because that would still leave one non-working fridge.
Partial conclusions:
F-controller isn't to blame as Combination #3 works
F-compressor actually works as Combination #2 works

Power draw
I hooked up the ammeter on the overload fuse, and right at starting, it read 10,69A, which is a tad below the 11A marked on the compressor.
IMG_1905.JPG
About half a second later, as the compressor has started, it almost instantly falls to 0.7A.
Then the compressor stops (total run time about 15 to 20 seconds), and fails to restart. Each time there's a slight hum and vibration going through the compressor, the ammeter reads about 7,5A.

Since it runs for a very short time, it doesn't have the time to heat up. Of course, I didn't try to leave it plugged as I think locked electric motors would destroy them from overheating (I broke three fans that way). I guess that would rule out compressor overheating.
And since amperage going to the compressor oscillates between 0A to 7.5A when it tries to restart

As for this special PTC (reference number: QPE2-A4R77MD3), here's a hand-drawn schematic (start capacitor is in red - or is it a run capacitor?):
IMG_1906.JPG
And a picture of the real thing. The very small gray cylinder on the left is connected to the TRIAC's gate:
IMG_1907.JPG
TBH I struggle to understand the electrical principle of this schematic.

Winding resistance
common-start: 5.7Ω
common-run: 5Ω

I know that some fridges (different brands / models) do trigger a defrost cycle almost immediately after being plugged in, but of course, they wouldn't try to run the compressor at the same time, so I ruled out that hypothesis.

For some reason, I was under the impression that trying to restart a stopped compressor too soon would fail as the start relay would prevent current from flowing to the "start" winding, and that leaving current flowing through the "run" winding wouldn't generate enough heat to destroy the compressor.

Not tried
If you think it would be useful, I could try to modify a start relay so as to measure current specifically getting to the "start" winding.
Replacing the start relay+overload+start capacitor with a "hard start kit", as you advised this summer in another topic.

How is a "hard start kit" normally used? As a testing tool only, or a one-size-fits-all repair?

Your thoughts?
 

Dan O.

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Cubytus said:
here's a hand-drawn schematic

I've never heard of a refrigerator relay using diodes. If it is some special compressor design, I can't help you with it.


How about posting the actual wiring diagram from the refrigerator?


Cubytus said:
Winding resistance
common-start: 5.7Ω
common-run: 5Ω

Those resistance readings of the compressor windings seem very high. If it is a standard compressor design, IMO it is likely defective.

Here are typical compressor resistances.
image.jpeg


Cubytus said:
Here are the combinations I tried.

I'm sorry but I don't know what that chart indicates.


Here's the bottom line in my opinion; If there IS power (120v) at the compressor (ie. the two wires going to the relay/overload) but the compressor is NOT running while still receiving power, the problem is either the compressor or the starting device. (BTW. Once the overload cuts out the compressor will draw 0 amps.)


That is all assuming it uses a normal compressor.

Dan O.
 

Cubytus

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Joined
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Messages
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Location
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Wiring diagram: (Ignore the door switch)
FaceAvant.jpg
Original, for reference.
IMG_1711.jpg
About the combinations: the two fridges in their original state are the first two columns. The remaining three columns show the different combinations of parts I mounted in a given chassis. Since it's impractical to dismantle compressors, the first row below the header gives away the refrigerator chassis the parts were mounted in.

In each row, the components that were swapped from one unit to another. The KG-prefix refers to the Known Good refrigerator, the F- prefix refers to the failed refrigerator. That doesn't mean that particular part has failed! It is just a practical way to have an unique ID for otherwise identical parts without having to write their serial number.

Last row gives the result. As you can see, the compressor in the "failed" refrigerator actually works under certain combinations.

Winding resistance : I wouldn't trust the multimeter too much with such low values. It's a decent multimeter, but not a Fluke or similar, precision-grade one. Besides, these resistances are still within the range you provided. Alas I don't have the other, Known Good unit to test it against.

Voltage at the compressor: During its very brief runtime, I get a reading slightly above 108V between "common" and "main", the same voltage as the mains.
When the compressor vibrates but doesn't actually run, I read 99.8V.
How would the voltage get so low, since the "common" compressor pin is energized by a relay? From experience, even pulling 1,200 W from the same outlet only reduces the voltage down to 107V.

Special compressor? You tell me.
In my mind, "special" is always more expensive than "mass-produced", so I don't see a reason why it would make its way in a budget-priced refrigerator.
EHZ80H1Z has the following parameters in GMCC's list:

What is the difference between RSIR and RSCR?
Captura de pantalla 2021-01-26 a las 21.37.17.png


Can you explain me the electrical operating principle / benefit of the start relay I drew earlier? The original diagram functionnally assumes a PTC, but the real circuit is the one I drew earlier and reproduced here for clarity. The larger PTC hooked up on T2 is 4.7Ω, the smaller one on G is 1.6kΩ. Does it act like a single PTC, as the original wiring diagram suggests?
My partial understanding is that either PTC will heat up faster than the other, and turn off current, either aby cutting current flow returning from T2, or by turning off the gate.

Since both the compressor and the controller appears to be good when installed in another refrigerator, and that I replaced the relay with a brand new one…
Do you have any idea what else I could try?
 

Dan O.

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I wouldn't trust the multimeter too much with such low values. It's a decent multimeter, but not a Fluke or similar, precision-grade one. Besides, these resistances are still within the range you provided.

The start winding should be 2 to 3 times the resistance of the run winding. Your readings were almost identical.

If your meter doesn't have a 1x ohm scale you should probably get a different one. It doesn't need to be a Fluke or any other specific brand just have a minimum restistance scale. The meter I used most cost $15. You rarely need anything fancy for appliance repair.


As you can see, the compressor in the "failed" refrigerator actually works under certain combinations.

If the compressor starts and will run for an extended period of time (not just momentarily) functioning normally with a different relay installed, the relay is the problem.

As I stated previously, if power is getting to the compressor but it is not running, either the relay/overload or the compressor is the problem. If the compressor will operate properly for an extended period, it is likely not defective .... Pointing to the relay as the likely cause.

Can you explain me the electrical operating principle / benefit of the start relay I drew earlier?

No I can't. I have no idea why it would have diodes in it. I do not disassemble parts to see what they're made of. If a relay is suspected of being defective it gets replaced with the correct one going my model number and part number. I put in whatever the factory supplies for it.


Dan O.
 

Cubytus

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Messages
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Location
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Multimeter: I guess the 200Ω range would be the equivalent of 1x? There's no lower one.

Compressor: you're right, I should have specified "WORKS" refers to an extended runtime period. In these combinations, the compressor ran as long as necessary to get the fridge compartment to the set temperature, then interrupted every 23 to 25 hours by a defrost cycle. In the "Failed" state, the compressor only runs for a short period. In both cases, power initially reaches the compressor, but in the second state, the controller cuts power for an unknown reason.

I'm still not sure why the "hum-no-run" condition results in such a large voltage drop. The controller only switches a relay, closing off the circuit from phase to comp.

Windings: Nothing in the graph refers. Do these values assume a traditional compressor type? Others on this forum and elsewhere have found different values, but nowhere as much as 2x to 3x difference.

BTW, what are RSIR and RSCR compressor types?

Start relay: from your experience, how likely is it to get 3 bad replacement relays? One repaired, two brand new?

Update:
Since F-compressor, F-controller are working and the start relay has been replaced, I followed the wiring diagram again, and unplugged the freezer fan so as to remove another variable. Somehow, the compressor turned on and ran for hours continuously, until I unplugged it (Fridge compartment wasn't at the set temperature, but that was to be expected, not having a functional fan).

I tested the fan separately on a 12V bench supply, and most of the time, the blades oscillated, but wouldn't turn. Amperage ran around 400 to 650mA, significantly above the 4W printed on the label. The shaft itself isn't locked, and hand-turning it yields no resistance whatsoever. After a few seconds plugged but not turning, the bottom right corner was extremely hot (pic for clarity, not the fan motor in question). A few times, I managed to get the fan running by hand-launching it, but speed kept on oscillating.

410CSSMvNJL._AC_SX355_.jpg


Hypothesis: It seems the issue has nothing to do with the compressor or relay at all: the controller seemingly performs a self-test on power-up, and un-graciously cuts power to the compressor when the fan can't run, and periodically tries to restart both (but happily keeps compressor powered when fan is entirely absent. Go figure.)

My next test: replacing the failed motor by another from another fridge.
 

Dan O.

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Multimeter: I guess the 200Ω range would be the equivalent of 1x? There's no lower one.

It is 200 x 1x

Others on this forum and elsewhere have found different values, but nowhere as much as 2x to 3x difference.

image.png

3 ohms is 3 x 1 ohm. On the other end of the scale 11 ohms is more than 2 X 5 ohms.

There is a ratio between the resistance of each winding. They're not just any resistance in those ranges. If the run was 1 the start might be 3, if the run was 2 the start might be 5, etc. But it's pretty pointless anyway if you can't even actually measure them.


Listen, I'm not an engineer, I didn't design the product, I didn't make the product, I'm not qualified to teach the subject. I am just an appliance repairman. My experienced opinion is if power IS continually going to the compressor, it SHOULD BE running. If at any time power IS there (at the compressor) but the compressor is NOT operating, the problem is with either the compressor or relay/overload.

If the control was responsible for stopping the compressor, all it would do is cut ALL power from even getting to the compressor.

So the bottom line is, is power getting to the compressor when it should be running or not? NO power = control system. YES power = defective compressor or relay asm. Period.


Any other answers you want you'll have to search the Internet. Sorry

Dan O.
 

Cubytus

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Messages
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Location
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It's true that applying power to the compressor should make it run. During these "hum-no-run" cycles, it receives about 750W, much higher than the normal 85W. A refrigerator compressor needs to have some resting time for pressures to equalize to be able to start. Does the very short cycle time allowed by the ePTC prevents the compressor from starting against pressure?

About the TRIAC-based PTC: documentation isn't very informative, but two compressors manufacturers, Secop and Danfoss mention an ePTC, which indeed acts as a standard PTC, but with less heat loss and shorter cycle time. My uneducated guess may have been correct after all. Why manufacturers would install an additional component to save 2W is beyond me however. I don't know yet if this ePTC can be replaced by a standard one, as the latter is very common, just in case the OEM ePTC isn't available. Relying on OEM parts, while usually desirable, isn't always possible: brands and manufacturers may offer no support at all, use rare parts, or chronically faulty ones. Between throwing away a minimally-defective fridge, losing 1 or 200$ worth of food in the process (More, if it's a larger fridge), and trying my best to make it run and extract a few more months/years of service out of it, I tend to chose the latter. Only when the compressor isn't compressing anything that I will consider it toasted.

RSCR: Resistance start – capacitive run For higher efficiency the auxiliary winding is supporting the main winding by a run capacitor (From Secop documentation). These look like the "high-efficiency" compressor types modern firdges use.

I get you, though.
Altough not in any technical trade, I like to know why stuff fails prematurely and asking on an appliance repair forum hosted by repairmen seemed like a good way to go. Sorry if I wrongly assumed any repairman experience would be better than my 7-fridges one.

As a repairman, given these symptoms, no service manual, no available parts, an unused refrigerator, would you have thought the fan motor would turn out to be the faulty part, turning a $600 replacement refrigerator into a much more reasonable $50 replacement motor?
 

Dan O.

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Cubytus said:
During these "hum-no-run" cycles, it receives about 750W,

It consumes...

It's trying to run but can't and thus it draws more power until (likely) the overload protector cuts off the power due to excessive current draw. That's the overload's purpose.

Cubytus said:
Does the very short cycle time allowed by the ePTC prevents the compressor from starting against pressure?

There is nothing that monitors refrigerant pressure. If the pressure it too great, the compressor will draw excessive current and the overload protector will cut off the power supply until it resets and tries again. It will continue to try until the compressor starts, the relay or overload fail outright, or the compressor does.

Cubytus said:
would you have thought the fan motor would turn out to be the faulty part

No I wouldn't and i do not see how it is possible the fan could be responsible for stopping the compressor when the compressor was still receiving power.

Did the motor fix it?


Dan O.
 

Cubytus

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Consume is the right term. Electrical power isn't received, but consumed (That's high school physics for me!). That's what I thought when I looked different schematics at how fridges operate: only time allows for pressure equalization through the capillary tube. A few minutes will do, though probably not 3-4 seconds. Compressor starting power appears to be 1300W, but running power is 85W.

My interpretation as to why the compressor wouldn't run a few seconds after stopping : the ePTC prevents current from reaching the "start" winding too soon. As a result, despite drawing so much power, the "run" winding doesn't have enough torque on its own to turn the compressor, especially if it's against pressure.

As to why the failed motor would stop the compressor: It's a low-voltage motor, so can be driven from a power transistor, not a relay. Somehow the electronic controller either 1- senses the excess current going through the motor, and tries to power-cycle compressor + fan motor (sounds real stupid to me), or 2- doesn't sense anything, and the controller just endlessly restarts because the low-voltage power supply contained within cannot power both a shorted motor, the controller itself, and keep the compressor relay in the "closed" position. The latter sounds more realistic to me as it's the simplest explanation.

As said, I replaced the motor using one from a trashed Danby: same shaft and fan, but different body shape: I had to cut the Insignia plastic bracket to fit it and keep the connector from the Insignia.

So far it appears to be running smoothly, but before claiming a successful "fix", I will have to leave it running for a few days with a temperature logger inside.

IMG_1909.JPGIMG_0721.JPGIMG_0720.JPG
 

Dan O.

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the controller just endlessly restarts because the low-voltage power supply contained within cannot power both a shorted motor, the controller itself, and keep the compressor relay in the "closed" position. The latter sounds more realistic to me as it's the sim

The machine's wiring diagram you posted shows the motor connected directly to the control. If the motor was somehow causing the compressor to stop, the power to the compressor would have to be stopped at the controller.

If there IS power at the compressor, it is not the control stopping it. If there's power at the compressor it should be running or the problem is at the compressor or the relay/overload.

I'm glad you're satisfied with your repair. I hope it contunues to operate.


I can't do anything more for you. Good luck!


Dan O.
 

Cubytus

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Did the motor fix it?
After a few days with the logger inside, I downloaded the data, and can confirm the fan motor replacement appears to have fixed it.
Captura de pantalla 2021-02-08 a las 4.34.00.png

One can see the moment when I put the logger in the freezer, then the fridge compartment, freezer again with these wild temperature swings as there's no fan to push some of the cold air in the fridge compartment. When the fan is replaced, freezer temp is much more regular, with the defrost spike every so often.
The machine's wiring diagram you posted shows the motor connected directly to the control. If the motor was somehow causing the compressor to stop, the power to the compressor would have to be stopped at the controller.

If there IS power at the compressor, it is not the control stopping it. If there's power at the compressor it should be running or the problem is at the compressor or the relay/overload.
You're right, that is probably what was happening: power was cyclically cut at the controller level, not at the compressor level. So the compressor doesn't receive a continuous 120V a whatever power it happens to draw, but rather, an intermittent 120VAC.

In fact, the controller does power-cycle itself with only the motor fan connected and compressor disconnected.

A refrigerator (or A/C) compressor cannot be power-cycled at will every 20 seconds, can it? The PTC would prevent the "start" winding from being energized too soon, leaving only the "run" winding connected. And on the "hot" wire, the overload protector would eventually cut all current flowing through the compressor if the overcurrent condition lasts long enough, though I am unsure under how much current and after which delay an overload fuse will turn off.
 

Dan O.

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So the compressor doesn't receive a continuous 120V a whatever power it happens to draw, but rather, an intermittent 120VAC.

That is what I originally asked as it would point to what is responsible for the problem, the control system or the compressor.



A refrigerator (or A/C) compressor cannot be power-cycled at will every 20 seconds, can it?

Not and work, no. It could also permantly damage the compressor if allowed to continue.


the fan motor replacement appears to have fixed it.

Glad to hear it. Thanks for the followup.


Dan O.
 

Dan O.

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My point was if power to the compressor was cutting out, it was the control that was doing it in which case looking into why would have be next, instead of focussing on diodes in the compressor relay and the compressor's functioning.

I would not however have suspected the fan motor being responsible but at least we wouldn't have been wasting our time considering the compressor. As I said, "If there's still power at the compressor when it stops operating, the problem is at the compressor. The control system would stop power from even getting to the compressor."


I'll try to keep a DC motor in mind for other control system malfunctions on models that use them.


Dan O.
 
Last edited:

water2xu

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Hi cubytus, I have the exact same problem with my new Insignia NS-RTM18WH8Q refrigerator as you described since my refrigerator was shutting down for the last winter in my cottage. I checked the fan motor and it seems seized. I use my finger to force the fan running and the refrigerator start to working. I really appreciate your experience and you save me money to buy an new refrigerator. I will get a spare motor fan part later when I get chance, just in case to replace it next time. Thanks you a lot.
 

Cubytus

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@water2xu, now that's weird. Does your model use the same motor? Would Insignia unknowingly mounted a bad batch? I don't see why a lightly-used, sealed brushless fan motor suddenly fail to run.
 

Dan O.

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Insignia NS-RTM18WH8Q appears to have been made by Midea offshore.

Motor # 502404010024 looks to have been substituted to # 11002015002201 which is listed as NLA at several suppliers. The 502404010024 motor looks to be available on eBay from China. I can't find anyone else selling that part #.

LINK > 502404010024 Fan Motor

A Danby model fridge looks to use the 11002015002201 motor which shows in stock at their supplier in Canada:

LINK > 11002015002201 Motor (no pic)


I don't know anyone else selling Midea parts.

Dan O.
 
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