I have been having defrost problems with my GE fridge for ~2 years. During this time, I have simply emptied the freezer, defrosted, and started back up. The unit would eventually fail to cool again, sometimes after a few months and sometimes after only a week. In all cases, both the freezer and refrigerator warm up together, so the problem is not isolated to one or the other.

I have recently discovered through this forum and other sources on the internet how to debug for defrost problems. Unfortunately, everything that I have checked so far seems OK. The heater/thermostat appear good, measuring ~22 Ohms at the J1 cable at the main board, and the thermistors also measure correctly. In fact, I bought a thermistor to replace the evaporator one, suspecting this as the problem. I clamped the new and the existing ones together, let the unit run for a while to stabilize temperature, and then measured both thermistors; they both read virtually the same impedance. Finally, all fans appear to be running correctly.

Based on this info, I am wondering whether the heater is ever getting turned on. Is there a way to force the heater on so that I can verify whether it is getting powered? Is the power applied through one of the relays on the main board? I would love to get a wiring diagram, main board schematic, and/or service manual to assist in the diagnostics.

I have little desire to simply replace the rather costly main board. I am an electrical engineer and am capable of repairing the board if I only know what to look for. Before these defrost problems began, the refrigerator quit working because the input flyback converter that generates the 14V to power everything failed. I repaired and improved the flyback design and also had to replace the ice dispenser solenoid at that time. Perhaps the heater control relay was overstressed when the converter failed. Other than the defrost issue, the unit has continued to work fine since my original repair.

I appreciate your assistance in fixing this problem.

Thank you for the links to the manuals and the feedback. Hopefully, I will be able to figure out my problem with this diagnostic help.

This morning, my hypothesis from yesterday about the heater not being activated was blown out of the water as I found the coils completely defrosted when I opened the freezer. The condenser was not running, and the freezer temp was at 2° when I first opened the door. The condenser came on after a few minutes but the temperature rose to 7° before I left for work; it is now back to 5° after ~2.5 hours. Frost was on the coils, and it seems to be operating correctly. The freezer is nearly empty, so I expect that this accounts for the wide tempertature swings, as the refrigerator is currently at 35° with a setpoint of 37 or 38.

This doesn't seem consistent with my previous defrost problems, but maybe I have reconnected something during my testing. As I reported yesterday, there is continuity on the defrost thermostat (which I only measured along with the heater). Since the freezer set point is 0°, I assume that it is normal for the hysteresis to be a few degrees before the condenser cycles back on. Is this correct?

Thanks again!