I have a Norcold 1200 with a strange problem. The cooling unit will operate and cool down to around 35 degrees (or slightly lower) and work fine for about a week. Then suddenly the temperature inside will start climbing and get into the mid 50's and the cooling unit will not engage because the thermistor temperature reads 15 degrees (using the diagnostic mode). Upon opening the door (light comes on) the thermistor temperature will jump to 10 degrees. If I toggle the door switch (causing the light to go off and back on) (either door), the thermistor will suddenly switch to reading 45 degrees and the cooling unit will come on. I've changed the thermistor, I've checked the connector plug (playing with the connector plug has no effect when the thermistor is reading incorrectly). Problem persists. Only opening and closing either door will cause the thermistor to snap out of it's problem and read correctly, and therefore cause the cooling unit to operate correctly. :h

They go through auto-defrost modes at times although that wouldn't explain what the thermistor is doing. Still, maybe that's what you're seeing?

ScottG wrote:They go through auto-defrost modes at times although that wouldn't explain what the thermistor is doing. Still, maybe that's what you're seeing?no because once it starts doing this, the temperature continues to climb. I am familiar with the defrost cycle, but that is not what this is. During the auto defrost, it will get around 42, but not 55 and thermistor read 15. And as soon as I turn off and on the light (pushing the door button in and out), the thermistor immdiately displays correct temp and cooling unit comes on immediately.

I don't know if this is plausible, but---Is the thermistor losing its power over that week where the light bulb snaps in? The light has the same power at the other end of the light bulb holder. Maybe the light comes on and kickstarts it.

BFL13 wrote:I don't know if this is plausible, but---Is the thermistor losing its ground over that week where the light bulb snaps in? The light has the same ground at the other end of the light bulb holder. Maybe the light comes on and kickstarts that ground.It appears to be something very close to what you are describing, but I cannot figure out what to do about it.

Sorry, had to edit out that being the ground. Same idea though. How about moisture/icing up there?

Norcold 1200 Thermistor reads wrong until door opened/closed

kmb1966
Explorer
Mar 08, 2020
dougrainer wrote:
1. Remove the Bulb from the light and see if the problem goes away
2. If not, then the odds are the rear Main board is bad
3. Long shot, would be corroded wire harness from the evap area thru the insulation of the box to the board. THIS is not a serviceable part.
4. How old is the refer?
5. Is the control board original? It is a Norcold board? Doug

Thank you for the advice.
Will try removing the bulb and re-test.
The Norcold is a 2003, so it is old. On it's 3rd cooling unit (Amish)
Yes the board is a Norcold board.
dougrainer
Nomad
Mar 07, 2020
1. Remove the Bulb from the light and see if the problem goes away
2. If not, then the odds are the rear Main board is bad
3. Long shot, would be corroded wire harness from the evap area thru the insulation of the box to the board. THIS is not a serviceable part.
4. How old is the refer?
5. Is the control board original? It is a Norcold board? Doug
BruceMc
Explorer III
Mar 06, 2020
Just guessing in the wind, but it sounds like the logic board is faulty.
RLS7201
Explorer II
Mar 06, 2020
There is a reset procedure for Norcold circuit boards that may help. Just guessing but it's a cheap try.

Richard
kmb1966
Explorer
Mar 06, 2020
dougrainer wrote:
kmb1966 wrote:
BFL13 wrote:
I don't know if this is plausible, but---Is the thermistor losing its ground over that week where the light bulb snaps in? The light has the same ground at the other end of the light bulb holder. Maybe the light comes on and kickstarts that ground.

It appears to be something very close to what you are describing, but I cannot figure out what to do about it.

There are 4 wires. 2 for the Light assbly. 2 just for the Thermister. Both are separate from each other. Are you positive the Thermister is installed correctly on the Fin? Are your cooling fans operating? The White and Black wire bundle for the light and rear fans can be swapped by mistake on the rear control board. This will cause no obvious problems except the rear fans will not come on. Maybe it also causes your Thermister problem? The large white/small white goes on the LEFT terminal facing the control board. Doug

Both fans in the rear are coming on.
Thermistor is on the correct fin, and in the correct position.
Thermistor was the first thing I replaced when this odd situation starting happening.
Watching the thermistor temperature (in diagnostic mode (3)) the temperature will show oddly low readings (00, 11, 15) and upon opening the door(light comes on) thermistor will read 15, 18, and then if I push the door switch(plastic white door switch) causing the light to go off (no change), but then release the door switch(causing light to come ON) the thermistor will jump to the correct reading (usually in the 40's) and the cooling unit will come on. All is well for a few days, and then it happens all over again.
dougrainer
Nomad
Mar 06, 2020
kmb1966 wrote:
BFL13 wrote:
I don't know if this is plausible, but---Is the thermistor losing its ground over that week where the light bulb snaps in? The light has the same ground at the other end of the light bulb holder. Maybe the light comes on and kickstarts that ground.

It appears to be something very close to what you are describing, but I cannot figure out what to do about it.

There are 4 wires. 2 for the Light assbly. 2 just for the Thermister. Both are separate from each other. Are you positive the Thermister is installed correctly on the Fin? Are your cooling fans operating? The White and Black wire bundle for the light and rear fans can be swapped by mistake on the rear control board. This will cause no obvious problems except the rear fans will not come on. Maybe it also causes your Thermister problem? The large white/small white goes on the LEFT terminal facing the control board. Doug
BFL13
Explorer II
Mar 06, 2020
Sorry, had to edit out that being the ground. Same idea though. How about moisture/icing up there?
kmb1966
Explorer
Mar 06, 2020
BFL13 wrote:
I don't know if this is plausible, but---Is the thermistor losing its ground over that week where the light bulb snaps in? The light has the same ground at the other end of the light bulb holder. Maybe the light comes on and kickstarts that ground.

It appears to be something very close to what you are describing, but I cannot figure out what to do about it.
BFL13
Explorer II
Mar 06, 2020
I don't know if this is plausible, but---Is the thermistor losing its power over that week where the light bulb snaps in? The light has the same power at the other end of the light bulb holder. Maybe the light comes on and kickstarts it.
kmb1966
Explorer
Mar 06, 2020
ScottG wrote:
They go through auto-defrost modes at times although that wouldn't explain what the thermistor is doing. Still, maybe that's what you're seeing?

no because once it starts doing this, the temperature continues to climb. I am familiar with the defrost cycle, but that is not what this is. During the auto defrost, it will get around 42, but not 55 and thermistor read 15. And as soon as I turn off and on the light (pushing the door button in and out), the thermistor immdiately displays correct temp and cooling unit comes on immediately.

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Norcold 1200 Thermistor reads wrong until door opened/closed

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