NS-RTM12SS7-C Need help identifying Insignia fridge GE-built?

Cubytus

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Where should the defrost sensor be located, normally? Is the side of the evaporator coil the right place?

This Insignia fridge has both a defrost sensor and a defrost fuse. The latter is a SHENG PING SPF70 TF 73ºC 10A 250V 15A 125V.
I tested both fridge and freezer thermistors, and they give similar values:
14KΩ@-12º 7,5KΩ@5º 1,94KΩ@25º
In other words, the freezer sensor doesn't appear to be broken, yet defrost starts way too often, and stops much too late. Should I replace the sensor, the (back-ordered) board, both?
 

rickgburton

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The defrost sensor is normally located on the evaporators lastpass. The defrost thermistor is used to terminate the defrost cycle.
Samsung thermistors -12°C = 22.3KΩ----- 25°C= 5.0KΩ
LG thermistors -12°C=50.1KΩ ----- 25°C=10.7KΩ
LG defrost thermistor:
43707

Cubytus said:
Should I replace the sensor, the (back-ordered) board, both?
Both unless you can fine a tech sheet or wiring schematic. Even then there's no guarantee that will solve your problem. Look on the compressor or model tag and see if it uses R134a or R600 refrigerant.

I should add this; If the defrost thermistor is mounted to the evaporator, the evaporator temperature is about 20°-30° colder than the compartment temperature.
 

Cubytus

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Could be an LG defrost thermistor, but there's no marking on the metal case. Your chart only gives values for very low temperatures. Obviously entry-level household regrigerators cannot reach such lows. I tested it by placing it in my own freezer, but not on the evaporator itself as the freezer is full :)

This Insignia uses refrigerant R600a, but does it really makes a difference as the sealed system is OK?

The sensor does appear to be mounted somewhere on the last pass, though not on a naked portion of the tube. Would its factory location be sub-optimal? I mean, it's not exactly over the heater (See picture)
IMG_1773.jpg

As for the wiring schematic, parts are approximately drawn where they are located when looking at the front of the fridge.
Notes:
There's a pair of white wires that appear to end between the fridge walls. I don't know if they connect R sensor or TH sensor (User manual states it's an ambient temp sensor) (See other wiring schematic from the back of the fridge).
The door switch doesn't appear to play any role in defrosting. In fact, the lamp works even with controller removed.

Images.jpg
IMG_1711.jpg
 
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rickgburton

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Cubytus said:
Obviously entry-level household regrigerators cannot reach such lows
You better look at the chart again. If your refrigerator can't reach 32°F in the freezer section you have a bigger problem. Normal is around 0°F. The actual temperature of the evaporator coils when the machine is running is -20°F to -30°F.
 

Cubytus

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Do you mean I should test the sensor in situ with fridge running? In other words, should I attempt to get another data point for very low temps? Or find the lowest temperature the evaporator can go on an empty compartment? Do you think that, somewhow, very low temperatures may not be read correctly?
 

Cubytus

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I answered your questions to the best of my knownledge. You asked for the wiring diagram to help find what could be the faulty part and the refrigerant used in the fridge, I found / drawn both.

But how does that help in answering the question:
What should be replaced in that fridge to make it functional again?
And also: why would such a recent fridge fail to defrost properly?
 

rickgburton

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OK, Let's recap and in simple sentences; You have a defrost problem where you think it defrosts too often. Since the machine does defrost, we can rule out the defrost heater and defrost fuse. That just leaves the defrost sensor/thermistor and control board. Since we don't know the actual manufacturer of the machine and can't look up any parts, I gave you the thermistor values for LG and Samsung sensors/thermistors because they both are manufacturers of Insignia. A defrost sensor is attached to the evaporator coil. I gave you the value for the lowest temperature you measured, -12°C and room temperature 25°C. I got the wiring diagram. Unfortunately it's not a wiring schematic and shows no values. According to the wiring diagram the TH-Sensor, the R-Sensor, the Fan motor, and compressor have absolutely nothing to do with the defrost cycle. If you can't determine if the defrost sensor value is correct or not, replace it.
Cubytus said:
This Insignia uses refrigerant R600a, but does it really makes a difference as the sealed system is OK?
I don't know if the sealed system is OK. Do you? If there was a refrigerant leak and the evaporator didn't have a full frost pattern, the symptoms would be the same.
Cubytus said:
test the sensor in situ with fridge running..... get another data point for very low temps? ......lowest temperature the evaporator can go on an empty
What the hell is that all about?? I don't need any of that information.
 
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