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ZISS420DRGSS GE Refrigerator - Heavy Frost on Evaporator

luckysam

Premium Member
Joined
Sep 4, 2020
Messages
3
Location
San Ramon, CA
Model Number
ZISS420DRGSS
Brand
GE
Age
More than 10 years
This is a 15-year old GE monogram side-by-side. A couple of years ago technician replaced inverter box.

About a couple month ago, we had a warm refrigerator. We bought an extra refrigerator so we can slowly fix this one. After being shut for a longer period of time, we got the refrigerator back to normal. (I didn't research enough. This should have indicate to check frost issue). Then in a couple month, we had a cold freezer (-4F) but warm fresh food (54F). I learned from this board; dissembled and replaced a broken damper (clearly broken; damper door can't open). Refrigerator didn't stop for more than 24 hours. I restarted the refrigerator and we can visually confirm damper door open. Air circling issue was solved. Now refrigerator has warm freezer (25F) and warm fresh food (46F).

Thanks for this board: I found a manual called zis360nm.pdf
I did what I can do so far: vacuumed condenser coil; visually checked the motherboard (WR55X10560, front and back has no visual burnt-out); visually checked evaporator fan spinning. After I finally touched Styrofoam insulation (not able to see evaporator drain pan), I could touch the evaporator foil and found thick ice. --- This must be root cause if not the only cause.

1. In "Heavy frost on evaporator" diagram at page 60 of zis360mn.pdf, one step is "Disconnect power. Unplug blue connector from main board. Measure between red wire on connector and orange (neutral) wire on main board Job 7, pin 9. Are there approximately 37 ohms?" In diagram of this link, it indicates "18-20 ohms. Anyhow I can't detect any resistance (J9 onboard and J7 orange pin).

2. I followed "Defrost Heater" path and got stuck at "Remove Stkyrofoam insulation from the bottom of the evaporator drain pan." My question is how I can proceed without damaging anything? In the power-off mode, how can I figure out "defrost heater" (where to test resistance?), and defrost overtemperature thermostat?

3. Now ice melted. Shall I at least put back the evaporator fan to power on? What test shall I do while it is on?

Thanks!
 

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Jake

Appliance Tech - Admin
Staff member
Joined
Aug 24, 2004
Messages
112,870
Location
McMullen Valley, Arizona
I can't detect any resistance (J9 onboard and J7 orange pin).
It's either the defrost heater, evaporator thermistor, or motherboard that is bad.

Your evaporator thermistor should be at about 16.3K ohms while its covered in frost.

Here's the evaporator thermistor for your model you can order:
WR55X10025 Temperature Sensor


Here's the defrost heater for your model:
WR51X322 Defrost Heater Assembly


Read this thread on how to access the defrost heater:

Also this one:

All you do is ohm test the 2 heating element terminal ends and see if you get less than 50 ohms on your meter. If so, the defrost heater is good. Make sure power to the refrigerator is disconnected before accessing and ohm testing those parts.

Watch this video to ohm test the defrost heater:

Jake
 

Jake

Appliance Tech - Admin
Staff member
Joined
Aug 24, 2004
Messages
112,870
Location
McMullen Valley, Arizona
Ok Sam, sounds good.

Jake
 

luckysam

Premium Member
Joined
Sep 4, 2020
Messages
3
Location
San Ramon, CA
Jake,
I followed J1-5 vs J1-4 resistance test. I had confirmed the evaporator thermistor is defect. It has 5.88k ohm at room temperature while other three sensors are consistent at 4.9k ohm. While dipping in ice water, the thermistor gave random readings. I also confirmed the consistence of the heater from inside freezer is good at 38.6 ohms. I can't test the thermostat because I couldn't get it off the evaporator.

I am ordering replacements and will update if replacing works. And I am clear about next steps: replace thermistor, if not working, replace thermostat; or further replace main board.

Thanks a lot!
-Sam
 

Jake

Appliance Tech - Admin
Staff member
Joined
Aug 24, 2004
Messages
112,870
Location
McMullen Valley, Arizona
Yes Sam, that is correct.

Jake
 
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