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Open Roads Forum  >  Tech Issues

 > Fridge Thermistor Replacement Question UPDATE (Fixed)

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BFL13

Victoria, BC

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Posted: 02/08/20 07:28am Link  |  Quote  |  Print  |  Notify Moderator

Updated 10 Feb. and 14 Feb

My 641 Norcold cools down too cold and won't shut off. It is not in back up power--the temp light does not flash.

I have not yet fiddled with the light/thermistor to see if it is just a bad connection.

There is a replacement part available. As a temporary fix if fiddling doesn't help, can I swap out the sensor (snip the wires) and replace with an old Dometic 6 cu ft fridge's sensor (splicing in its wires to the Norcold's)

AFAIK it is all about the resistance of the sensor, but no idea what the circuit board would think.

http://rvrefrigeratorrepair.com/wp-conte........ds/2016/08/Norcold-Service-N61x-N81x.pdf

Thanks

* This post was last edited 02/14/20 09:44pm by BFL13 *   View edit history


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cavie

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Posted: 02/08/20 08:37am Link  |  Quote  |  Print  |  Notify Moderator

thermister is probably bad. google "Snip-the-the tip". Should fix your problem.


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enblethen

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Posted: 02/08/20 08:42am Link  |  Quote  |  Print  |  Notify Moderator

I would get the correct part for your Dometic. Here is one listing from Amazon for Dometic.

Dometic thermistor
Is your circuit board an original Dometic?


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BFL13

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Posted: 02/08/20 08:54am Link  |  Quote  |  Print  |  Notify Moderator

Thanks. Also noted the way to measure its R. Heading out so no replies for a few days.

mchero

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Posted: 02/08/20 06:03pm Link  |  Quote  |  Print  |  Notify Moderator

Download the service manual.


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Posted: 02/10/20 07:59am Link  |  Quote  |  Print  |  Notify Moderator

Our Norcold 611V would freeze everything. A new thermistor didn't help and neither did adjusting it. The solution was to install an adjustable "optical controller board", I got the board under warranty & it was a 5-minute job to change it.


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wnjj

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Posted: 02/10/20 09:31am Link  |  Quote  |  Print  |  Notify Moderator

The couple of resistance charts I found showed the Norcold thermistor resistances don’t match the Dometic. So I’d say no, it won’t work to borrow an old Dometic one.

BFL13

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Posted: 02/10/20 01:00pm Link  |  Quote  |  Print  |  Notify Moderator

Yes it didn't work when I swapped to the old Dometic thermistor. I have not yet checked either one for R. Based on above posts, first I need to confirm the Norcold one is not right before getting a new one or one of those other gizmos.

Camping this weekend I just turned off the fridge when the fridge thermometer said it was getting too cold, and back on again later.

I am really mixed up on how the thermistor works. AFAIK they have more R when cold (at least those in-rush ones do), so that would mean the signal to turn off the fridge is when R gets that high.

But then, they say to move the thermistor up where it is warmer on the fins to make it shut off sooner. Makes no sense to me. Oh well.

http://rvrefrigeratorrepair.com/uncategorized/the-thermistor-shuffle/

BFL13

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Posted: 02/10/20 03:26pm Link  |  Quote  |  Print  |  Notify Moderator

According to this

http://bryantrv.com/docs2/docs/norcoldnxseries.pdf

At 70F it should be 11.1-12.0 kOhms. Mine is 8.2 kOhms
At 51F it should be 15.5-16.5 kOhms. Mine is 12.7 kOhms

At 70F the little Dometic one is 3.4 kOhms.

So assuming mine is out by having lower R on the whole range, then instead of shutting off the heat at 25, mine would still have been way lower so it never shut off. The little Dometic one would be even lower in R so it didn't do any good.

Perhaps my jury rig should have used both thermistors in parallel. ISTR they would add their Rs doing that. ??

Anyway, unless somebody says no, I plan to order the replacement thermistor part. I see in the manual above that it goes on the 10th fin from the right, at least to start with.

* This post was edited 02/11/20 05:41pm by BFL13 *

wnjj

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Posted: 02/10/20 07:32pm Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:

Yes it didn't work when I swapped to the old Dometic thermistor. I have not yet checked either one for R. Based on above posts, first I need to confirm the Norcold one is not right before getting a new one or one of those other gizmos.

Camping this weekend I just turned off the fridge when the fridge thermometer said it was getting too cold, and back on again later.

I am really mixed up on how the thermistor works. AFAIK they have more R when cold (at least those in-rush ones do), so that would mean the signal to turn off the fridge is when R gets that high.

But then, they say to move the thermistor up where it is warmer on the fins to make it shut off sooner. Makes no sense to me. Oh well.

http://rvrefrigeratorrepair.com/uncategorized/the-thermistor-shuffle/

The thermistors do get higher resistance when colder. As for moving it around on the fin, I think your confusion comes from interpreting their picture. The red area in the upper right is showing where you move the thermistor to make the fridge temperature follow the color (red=warmer). The upper right is also where the fin temperature is colder which in turn causes the fridge to cycle off sooner.

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