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FIXED ZIS420NMC 2003 GE Monogram Refrigerator - temperature issues

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Premium Member
Jan 28, 2021
Model Number
More than 10 years
Good day, my problem is actual freezer and fridge temps are MUCH different than the display temps and the freezer is getting way too cold before it cycles off and too hot before it cycles back on. Same problem in the fridge section.

The freezer section will pull down to -22 F before clicking off. The set point is set to max of 6 F. It will click back on at 9 F. The temperature display is always wrong- like if the freezer section is at -16 F it will read 12 F (I've never seen the display temp go negative) and at 7 F it will read 10 F. The temp display is also very slow to react to temperature changes. I've been leaving the fridge off all night and it will actually read correctly in the morning at 12 F or so. The freezer does react to my changing the set point- I can turn it off, and if I set the set point to say zero and I let the freezer cycle down to -28 F, I can increase the set point and it will cycle off.

The temp display in the fridge is also never right and very slow to react but is correct in the morning if I turn it off over night, etc- so like the freezer section. The fridge section gets down to 29 F to 30 F when the freezer is in the negative teens. Even if I set the fridge set temp to 45 F max, it doesn't keep the unit from cycling on as above.

I'm using wireless temp probes- I checked three against each other so I'm pretty close on my temp readings.

I did the diagnostics- 02 Pass, 03 and 04 Fail- but I don't have a dispenser, 06- all the LCD segments lit up, 07- All Pass, 08 and 10- I could hear the door cycle but the display didn't indicate anything. I've also thrown the fuse to the unit and waited 10 minutes or so.

3 years ago I had the damper changed and maybe some of the thermistors- not sure on those. I had a Sears guy come out this week and all he did was confirm the actual temps were far away from the temp display. He called into GE and told me I needed the HMI/temp control board part WR55X10159. But he said the part is no longer available so the fridge is dead. I've been looking far and wide for one with no luck yet.

So a couple of questions:
1. Could it actually be the motherboard or bad thermistors or something else?
2. Anybody know where I can get the part- new or used- or can it be rebuilt?
3. Can I instead buy the entire assembly the HMI board is in? If so, same question as #2.
4. I wonder if I could replace the assembly with any 42" Monogram part- might look different but function the same?

Lots of effort but the fridge is a custom cabinet build in and will be $$ and difficult to replace.

My model is ZIS420NMC


Corrected model number
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My model is ZI5420NMC
Recheck your model number for me. Nothing comes up with that one. Be sure to read it from the model tag on the machine.
Check for 13 VDC communication voltage across J4-2 and J4-3 on the main board. You can check the thermistors resistance matches the temperatures by measure each thermistor in the J1 connector. Disconnect the J1 connector and measure in the connector. J1-5 is common for all thermistors. I'll post a temperature/resistance chart. Here's the part you need:
WR55X11030 comm -volts thermistors.jpg


Here's the part you need:
Good morning, here's what I got. J4-2/J4-3: 13.4V. J1: 20.5 ohms, J2: 17.0 ohms, J3: 32.5 ohms, J4: 46.0 ohms. J1 @ 24 F, J2 @ 30.3 F, J3 @ 8.5 F, J4@ -2.5 F. Actual Fridge temp @ 30.1 F, Actual Freezer @ -5.6 F. Fridge dash reads Fridge @ 29, Freezer @ +5 F.

I don't know what to make of it- I could think that I have one bad freezer thermistor @ J3? But, not sure why the dash temps aren't the average of both? Plus, not sure why compressor still running with set point set at +6F? Thanks
Replace the main board.
Great, thanks very much.

So I understand the thermistor leads come directly to the main board, it converts ohms to degrees and sends the answer to the temp control board/HMI (in my case the main board is getting the conversion wrong)? And all the HMI does is display what the main board is sending and allows the cycle set points to be changed and sends that back to the main board? Also, I see two thermistors in the fridge section but only one in the freezer section on the middle inner side (mine is a 42"). Where is the 4th thermistor?

Finally, where there are two thermistors- does the main board take the average or use some sort of high/low logic?
Where is the 4th thermistor?
On the evaporator. The 13V communication voltage should also be present at the same J4-2 & 3 on the HMI board
Hey Rick, won't get the motherboard for a week or so, but for fun I reset from the diagnostics menu. I had flipped the fuse off for quite a while previously with no effect, but the reset changed things. The freezer is now cycling right- with the set point at 6 it will go up to 8 and shut off and come on again at 4 (using my temp probe). The indash temp display still seems off, but not by as much, and is till very slow to change though I don't know if that's an issue. Thoughts?
Check the wire connections on the boards Make sure they are on tight and none of the pins are starting to back out of the connectors. Look for cold/broken solder joints on the boards. Sometimes just checking the voltage is enough to make a bad solder joint work temporarily. Keep an eye on it. Unless there was some sort of glitch with the MICOM it will show up again.
Well, I installed the new motherboard and there is no difference. However, I have been more carefully tracking the temperatures by putting my probes just next to the thermistors. I now think the freezer is doing it's thing OK- how ever the temps are being calculated by the board and displayed seems to have some sort of long time averaging, but it does seem to hold the set temperature in a band of +2 and -2 degrees around the set point. The real problem is that the fridge side is too cold- just above freezing on average. I know the system is not thinking the fridge needs to be that cold- since the compressor doesn't cycle on for anything other than the freezer temps. I guess it sounds like a blend door problem? I did the diagnostic and heard them operate. Could it be a problem with the HMI board, or should I look more deeply into the blend doors? Or something else? Thanks!
Oh OK, got it. I was able to locate this service flash that includes your model number:


  • ZIS FF Compartment too cold REF18-03.pdf
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