Norcold 1200 - Thermistor temps wrong until power cycled

[kmb1966]

I am troubleshooting an ongoing problem with my Norcold 1200.
It cools fine for a few days and then suddenly will stop cooling. Putting the Norcold in diagnostic mode, the thermistor reading will show very low temperature readings. For example the thermistor temperature will show 11 degrees even though it is 58 degrees in the refrigerator and 45 in the freezer.

- If I turn the refrigerator OFF and then back ON using the control panel, it has no effect, thermistor temp is still wrong.

- If I disconnect the thermistor and re-connect it, the thermistor will read the correct temperature and the cooling unit will come on and cool fine for a few days and then suddenly start reading incorrectly again (very low) and therefore cooling unit won't come on.

- I've replaced the thermistor with a new one, and the new one does the same thing. Reads correctly for a few days and then starts reading very low and therefore cooling unit won't come on.

- I don't think the problem exists if the refrigerator is in LP-GAS mode. Seems to work fine all the time in gas mode.

- I do have an ARP (frig defend) device on the frig. Turning it off and back on also causes the thermistor to read correctly. I don't think the ARP has anything to do with this though because if I turn the ARP OFF altogether, the problem still happens.

Still testing.....

[kmb1966]

dougrainer wrote:

kmb1966 wrote:

dougrainer wrote:
Replace the Rear Control board. Remember the Thermister reading in diag mode is the FIN temp. The actual refer temp will be 10 degrees warmer. Also, a Defective Thermister will test(Ohm) out correctly. But, since you have replaced it, go with the control board. Are you positive the 4 wire quick connect by the interior light has good solid pin connections for the 2 wires to the Thermister? Doug

Hi Doug, Thanks for you input. I think that the connectors by the interior light are OK, (at least they look OK). But it is worth mentioning to you that the internal fans(2) from the ARP Device also connect to the black wire on this interior light. Perhaps that could be the cause of the problem?

Possibly. In 25 years of working on hundreds of 1200's I have never heard or seen this type problem. I thought you stated you disconnected the ARP device and it still malfunctioned? There are 4 wires Positive/Ground(2) for the light. The other 2 go to the Thermister and should not be affected since they are separate. I thought maybe the pins at the connector may have corrosion and causing lack of OHM signal. Doug

I have not disconnected the ARP unit, but I did simply turn it off and test with the same results. I think I should unwire the ARP unit and re-test, or at least unwire the 2 internal fans and re-test. What seems ODD is that I cannot get it to malfunction in the LP-GAS mode.

[dougrainer]

kmb1966 wrote:

dougrainer wrote:
Replace the Rear Control board. Remember the Thermister reading in diag mode is the FIN temp. The actual refer temp will be 10 degrees warmer. Also, a Defective Thermister will test(Ohm) out correctly. But, since you have replaced it, go with the control board. Are you positive the 4 wire quick connect by the interior light has good solid pin connections for the 2 wires to the Thermister? Doug

Hi Doug, Thanks for you input. I think that the connectors by the interior light are OK, (at least they look OK). But it is worth mentioning to you that the internal fans(2) from the ARP Device also connect to the black wire on this interior light. Perhaps that could be the cause of the problem?

Possibly. In 25 years of working on hundreds of 1200's I have never heard or seen this type problem. I thought you stated you disconnected the ARP device and it still malfunctioned? There are 4 wires Positive/Ground(2) for the light. The other 2 go to the Thermister and should not be affected since they are separate. I thought maybe the pins at the connector may have corrosion and causing lack of OHM signal. Doug

[kmb1966]

dougrainer wrote:
Replace the Rear Control board. Remember the Thermister reading in diag mode is the FIN temp. The actual refer temp will be 10 degrees warmer. Also, a Defective Thermister will test(Ohm) out correctly. But, since you have replaced it, go with the control board. Are you positive the 4 wire quick connect by the interior light has good solid pin connections for the 2 wires to the Thermister? Doug

Hi Doug, Thanks for you input. I think that the connectors by the interior light are OK, (at least they look OK). But it is worth mentioning to you that the internal fans(2) from the ARP Device also connect to the black wire on this interior light. Perhaps that could be the cause of the problem?

[dougrainer]

Replace the Rear Control board. Remember the Thermister reading in diag mode is the FIN temp. The actual refer temp will be 10 degrees warmer. Also, a Defective Thermister will test(Ohm) out correctly. But, since you have replaced it, go with the control board. Are you positive the 4 wire quick connect by the interior light has good solid pin connections for the 2 wires to the Thermister? Doug

[Chris_Bryant]

I’d check the solder joints where the thermistor plugs into the board- could be cracked.
Shot in the dark.

[DFord]

I'd check with ARP and Dinosaur Boards before condemning the controller.

https://www.dinosaurelectronics.com/Nor_boards.htm

https://www.dinosaurelectronics.com/contact_form.php

Dinosaur Boards Website wrote:
If you are in need of immediate technical assistance, or have not heard back from us in two business days give us a call between 8:00 am and 5:00 PM PST at: (541) 994-4344

[time2roll]

I would put a new control board in it.

[Flute_Man]

Sounds like the control board may be the problem. Have you been able to contact Norcold for their comments?