Interpreting resistance data for my freezer sensor
November 6, 2022 3:11 PM Subscribe
I ordered a replacement thermistor for my freezer, but decided to check it against the table in the service manual before installing it. I'm having trouble understanding the results, specifically why I'm seeing roughly twice the resistance I expect.
I'm measuring temperatures with two standalone thermometers and just in case I did check the Fluke with some known resistors. The data seems good.
The only thing slightly weaselly here is that the chart of expected values comes from the refrigerator service manual. I haven't found the specifications for the thermistor itself, I'm just assuming that since it's a drop in replacement for the existing thermistor it will match.
Any thoughts? I apologize for the limited data but the fact that there's nothing in the house below 20F right now it sort of the problem.
I'm measuring temperatures with two standalone thermometers and just in case I did check the Fluke with some known resistors. The data seems good.
The only thing slightly weaselly here is that the chart of expected values comes from the refrigerator service manual. I haven't found the specifications for the thermistor itself, I'm just assuming that since it's a drop in replacement for the existing thermistor it will match.
Any thoughts? I apologize for the limited data but the fact that there's nothing in the house below 20F right now it sort of the problem.
Why do you think this is the broken part? You could run the freezer with a fixed resistor installed and it should get cold (which would allow you to gather those missing data points.)
Is the temperature control digital or analog?
Unlikely, but, is the manual saying to measure the thermistor while installed?
I would not expect this part to work.
posted by flimflam at 6:05 PM on November 6, 2022
Is the temperature control digital or analog?
Unlikely, but, is the manual saying to measure the thermistor while installed?
I would not expect this part to work.
posted by flimflam at 6:05 PM on November 6, 2022
the chart of expected values comes from the refrigerator service manual.
Can you put this part of the manual somewhere on the net?
posted by Stoneshop at 1:18 AM on November 7, 2022
Can you put this part of the manual somewhere on the net?
posted by Stoneshop at 1:18 AM on November 7, 2022
Response by poster: Here's the whole manual. There's an abbreviated chart on on page 35 and the whole thing on 69.
Why do you think this is the broken part?
I want to be very clear (because I confused myself on this) that the actual diagnosis and repair of the refrigerator is not part of this question. The only way the freezer make and manual are relevant is that the manual contains a chart which I think should correspond to the part I ordered, and I ordered that part because it corresponds to the model described by the manual.
The only way the existing refrigerator is involved is in providing cold. I could be doing the same experiment using dry ice and the results would be equally confusing.
I would love to open up the basic troubleshooting problem, but that would begin with the question "Can anyone find me the service manual for a LG GC-M230LDW" and I feel like that would be too obscure even for this crowd.
posted by Tell Me No Lies at 8:47 AM on November 7, 2022
Why do you think this is the broken part?
I want to be very clear (because I confused myself on this) that the actual diagnosis and repair of the refrigerator is not part of this question. The only way the freezer make and manual are relevant is that the manual contains a chart which I think should correspond to the part I ordered, and I ordered that part because it corresponds to the model described by the manual.
The only way the existing refrigerator is involved is in providing cold. I could be doing the same experiment using dry ice and the results would be equally confusing.
I would love to open up the basic troubleshooting problem, but that would begin with the question "Can anyone find me the service manual for a LG GC-M230LDW" and I feel like that would be too obscure even for this crowd.
posted by Tell Me No Lies at 8:47 AM on November 7, 2022
Best answer: Your test procedure sounds reasonable. You verified that the meter is not giving bad readings by checking it with a fixed resistor. At this point, it's most likely that the new thermistor is the wrong kind /new defective out of box OR the service manual has the wrong data in it.
It seems like your options are pretty straightforward at this point. Buy another thermistor (ideally OEM not aftermarket) and bench test it the same way to compare it OR install the thermistor you have and see what happens (which is working off the assumption that the service manual info is wrong.) Speaking of which, it looks like the sensor data chart is on p.22. The values on p.69 seem really odd (they're in ohms, not k ohms) The chart on p22 implies that there is more than one type of thermistor in this appliance. Any chance you ordered the wrong one or the supplier sent you the wrong one?
posted by Larry David Syndrome at 6:19 PM on November 7, 2022
It seems like your options are pretty straightforward at this point. Buy another thermistor (ideally OEM not aftermarket) and bench test it the same way to compare it OR install the thermistor you have and see what happens (which is working off the assumption that the service manual info is wrong.) Speaking of which, it looks like the sensor data chart is on p.22. The values on p.69 seem really odd (they're in ohms, not k ohms) The chart on p22 implies that there is more than one type of thermistor in this appliance. Any chance you ordered the wrong one or the supplier sent you the wrong one?
posted by Larry David Syndrome at 6:19 PM on November 7, 2022
Response by poster: Nice spotting on that chart!
The part is theoretically OEM -- it was sold as that -- but I have my suspicions. In fact that's largely why I tested it in the first place.
If my testing sounds basically on track then I think picking up a few more sensors to test is probably the right way to go. The installed sensor reads zero ohms at all temperatures so it's getting replaced one way or another, but I'd like to have as much information as I can about what I'm putting in.
posted by Tell Me No Lies at 6:51 AM on November 8, 2022
The part is theoretically OEM -- it was sold as that -- but I have my suspicions. In fact that's largely why I tested it in the first place.
If my testing sounds basically on track then I think picking up a few more sensors to test is probably the right way to go. The installed sensor reads zero ohms at all temperatures so it's getting replaced one way or another, but I'd like to have as much information as I can about what I'm putting in.
posted by Tell Me No Lies at 6:51 AM on November 8, 2022
Response by poster: Just to share what little closure there is here, I did order the same part from a more reputable supplier. It showed up in the same packaging and exhibited the same results. I'm guessing I did not correctly identify the freezer sensor in the parts diagram. Since it's not even the right service manual I moved on.
A local group needs a big refrigerator and is fine with using the freezer part for just making ice, so off it goes.
Walmart was supposed to deliver a new refrigerator today. They showed up at 7:30pm with a washing machine. It's a fitting capstone to this process.
posted by Tell Me No Lies at 5:41 PM on November 16, 2022 [1 favorite]
A local group needs a big refrigerator and is fine with using the freezer part for just making ice, so off it goes.
Walmart was supposed to deliver a new refrigerator today. They showed up at 7:30pm with a washing machine. It's a fitting capstone to this process.
posted by Tell Me No Lies at 5:41 PM on November 16, 2022 [1 favorite]
This thread is closed to new comments.
If it's an aftermarket part, it's definitely possible that it's a bad substitute and is out of whack. (Once again, a non appliance reference- I used to repair a product which used battery packs with an internal thermistor. Some aftermarket packs were sold with a thermistor which was 1/5th the specified resistance at room temp. It didn't work! )
Good luck! Hopefully someone with more appliance repair experience will chime in with a definitive answer.
posted by Larry David Syndrome at 4:20 PM on November 6, 2022