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Old 06-23-2022, 07:03 AM   #1
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norcold thermistor question

It appears my thermistor decided to do its own thing. in my norcold 6121

Fridge wouldn't cool down at all and long story short.
I removed the thermistor from the cooling fins to test it.
Fridge cooled down over night, so I believe that is the issue.


How long can this thermistor be left off?

Reason for asking; down the road if this should happen to me again I can either shut it down/deal with food or disconnect it and let it blast to keep the temps down.
on side note.. how do things break sitting over a winter season -ok not a real question but frustrating..

The fridge worked well last summer, but over the winter
I lost an ignition board and now the thermistor. I hope the fridge is done acting out on me. haha
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Old 06-23-2022, 09:24 AM   #2
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The thermistor sitting on the rack or totally removed will make fridge's cooling unit run on max cool all the time. adjustments on the fin will result in a gradual change in cooling over at least 24 hrs. Here's a link you might like:


https://jc-refrigeration.com/product...free-shipping/
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Old 06-23-2022, 09:33 AM   #3
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Quote:
Originally Posted by puttin View Post
The thermistor sitting on the rack or totally removed will make fridge's cooling unit run on max cool all the time. adjustments on the fin will result in a gradual change in cooling over at least 24 hrs. Here's a link you might like:


https://jc-refrigeration.com/product...free-shipping/
You seemed to answer a question I wasn't asking.
but I appreciate it..



I am just curious if it will destroy the cooling unit if left like that for an extended time? Is it any different than setting it on the coldest setting and letting it run full blast that way on a hot day?
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Old 06-23-2022, 12:01 PM   #4
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Loss of Thermistor fed back results in fridge temp control running continuously which can result in over freezing or under cooling depending on which temp setting number at time of failure

Heat source duty cycle is based on TIME vs Temp upon failure of thermistor fed back
If TOO cold in food compartment...lower temp setting
IF not cold enough.....raise temp setting

Timed based is less accurate vs temp based control but at least fridge keeps working.
*Some models shut down if thermistor fed back is lost
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Old 06-23-2022, 12:11 PM   #5
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Originally Posted by Old-Biscuit View Post
Loss of Thermistor fed back results in fridge temp control running continuously which can result in over freezing or under cooling depending on which temp setting number at time of failure

Heat source duty cycle is based on TIME vs Temp upon failure of thermistor fed back
If TOO cold in food compartment...lower temp setting
IF not cold enough.....raise temp setting

Timed based is less accurate vs temp based control but at least fridge keeps working.
*Some models shut down if thermistor fed back is lost
Yes sir, I understand all that. This question is purely hypothetical, not that I anticipate the new thermistor to quit or I hope the new one doesn't quit that soon. So basically if it dies while on a start of a trip, there is no real harm in disconnecting it from the fin and letting it run full on.
If it starts to freeze up, I can lower the setting, if it isn't keeping up I can raise it again. I didn't think there was any real issue with such a scenario besides using more eletric/propane, at least my rudimentary understanding of the working of absorption fridges.
Thank you
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Old 06-23-2022, 12:45 PM   #6
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For $32 to have a spare thermister there is https://www.snip-the-tip.com/NorcoldThermistor.htm

Quote:
Originally Posted by inthepines View Post
Yes sir, I understand all that. This question is purely hypothetical, not that I anticipate the new thermistor to quit or I hope the new one doesn't quit that soon. So basically if it dies while on a start of a trip, there is no real harm in disconnecting it from the fin and letting it run full on.
If it starts to freeze up, I can lower the setting, if it isn't keeping up I can raise it again. I didn't think there was any real issue with such a scenario besides using more eletric/propane, at least my rudimentary understanding of the working of absorption fridges.
Thank you
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Old 06-23-2022, 01:01 PM   #7
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already ordered
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Old 06-24-2022, 08:40 AM   #8
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Thermistor

Quote:
Originally Posted by inthepines View Post
It appears my thermistor decided to do its own thing. in my norcold 6121

Fridge wouldn't cool down at all and long story short.
I removed the thermistor from the cooling fins to test it.
Fridge cooled down over night, so I believe that is the issue.


How long can this thermistor be left off?

Reason for asking; down the road if this should happen to me again I can either shut it down/deal with food or disconnect it and let it blast to keep the temps down.
on side note.. how do things break sitting over a winter season -ok not a real question but frustrating..

The fridge worked well last summer, but over the winter
I lost an ignition board and now the thermistor. I hope the fridge is done acting out on me. haha
One cause of thermistor failure is water infiltration.

There are two methods, one is melting front on the thermistor, the other is putting them in ice water to test.

We have sampled many thermistors and found the failure to be water some of the time.

Hope this helps
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Old 06-24-2022, 09:27 AM   #9
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One cause of thermistor failure is water infiltration.

There are two methods, one is melting front on the thermistor, the other is putting them in ice water to test.

We have sampled many thermistors and found the failure to be water some of the time.

Hope this helps
I just took it off the fins and it cooled down at least during the cool part of the day/night. Probably as good as it will get in an unconditioned camper and sun on it for better part of half a day.
My diy blower fan has been running nonstop, may add another fan but I'm not sure it will help much more. I already feel the air moving out of the chimney.

Haven't performed any other test, but if I was to test more I'd just ohm it out. I don' think I need to at this point though.


I imagine it failed though due to what you stated,condensation on the fins may have done it in. Not positive, just a guess.
No idea if the PO ever used an interior fan but I have one running in it.
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Old 06-25-2022, 12:50 AM   #10
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Quote:
Originally Posted by George Schweikle View Post
For $32 to have a spare thermister there is https://www.snip-the-tip.com/NorcoldThermistor.htm
Thermistors are 90 cent parts.

The most common type is 10K Ohm NTC.
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Old 06-25-2022, 10:59 AM   #11
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Fan Control

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Originally Posted by inthepines View Post
I just took it off the fins and it cooled down at least during the cool part of the day/night. Probably as good as it will get in an unconditioned camper and sun on it for better part of half a day.
My diy blower fan has been running nonstop, may add another fan but I'm not sure it will help much more. I already feel the air moving out of the chimney.

Haven't performed any other test, but if I was to test more I'd just ohm it out. I don' think I need to at this point though.


I imagine it failed though due to what you stated,condensation on the fins may have done it in. Not positive, just a guess.
No idea if the PO ever used an interior fan but I have one running in it.
As mentioned in the last post, the thermistor is rated at 10k ohms R25 value. I am going from memory, at 25C the thermistor reads 10,000 ohms.

See our engineered fan controller. The only time the fans will run is when they are needed. We make a small blower for inside the fridge, again engineered for the application.

Running fans full time is bad

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Old 06-25-2022, 11:10 AM   #12
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Running your fridge without the thermistor will cause it to run in full cool mode regardless of the temperature setting . It may freeze foods in the fridge compartment and ice up. You can run it that way , but you will have to monitor the temps. If it gets too cold just turn it off for a couple of hrs.
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Old 06-25-2022, 11:31 AM   #13
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Quote:
Originally Posted by Soppy View Post
Running your fridge without the thermistor will cause it to run in full cool mode regardless of the temperature setting . It may freeze foods in the fridge compartment and ice up. You can run it that way , but you will have to monitor the temps. If it gets too cold just turn it off for a couple of hrs.
You can make minor temp adjustments by changing the temp setting when fridge is in BOS (Backup Operating System) due to thermistor failure

Thermostat reverts to Time Based control vs Temp Based Control
Changing the Temp Setting affects the Time Duration.
Lower setting - less time heat is on ---less cooling
Higher setting - more time heat is on ---more cooling

**Some fridge models will just RUN continuously
**Some fridge models will STOP running w/o thermistor

Need to check manual for specific operation for ones model to verify how it will function w/o thermistor
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Old 06-26-2022, 07:30 AM   #14
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Originally Posted by Fridge Defend View Post

Running fans full time is bad
why would that be? I'd love to hear your opinion on this one.

I've been around computer/server fans for 2 decades so I'm curious.
Maybe it's because of this I don't see any issues letting fans run 24/7

Power consumption is negligible, if 1 amp +/- running 24/7 kills your battery bank than I think there are bigger issues that need to addressed.
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