I found an earlier thread that had similiar problems at forum.appliancepartspros.com/refrigerator-freezer-repair/468686-change-temperature-sensor.html

Following those instructions:
the defroster test (J9 and pin 9 of J7) = no resistance on 200 ohm scale.
The thermistor test (both evaporator and freezer) = no resistance 20K and 200K scale. (same as if I just touch the test leads together). It appears the thermistors are bad based on this test.

I also found: applianceassistant.com/ServiceManuals/31-9072_arctica_profile_ge_side-by-side_refrigerator_service_manual.pdf

Based on the service manual, page 52 Heavy Frost on Evaporator, I ran the diagnostic and the defroster did not come on (the area below the evaporator coils did not warm up after the door was closed for about 5 minutes. There was still frost on all over the coil.) The temp in the freezer based on the freezer's display changed from 0 to 16 F.

The wire to J9 and orange wire on J7 connector showed 0 ohms. With the fridge plugged in, the VAC across J9 and pin 9 of J7 showed 0 Volts VAC (on 200 volt scale). Should I have the connectors plugged into the mainboard and the fridge plugged in to get this reading or can I measure across the corresponding pins on the mainboard?

Just for kicks, I ran diagnostic 0 7 for thermistors and all 5 passed despite the zero resistance when measured across J1 pin 3 and 5, and J1 pin 4 and 5.
Do I need to replace the main board and the thermistors?

My wife is getting annoyed about not having a freezer/fridge every time I have to unplug to thaw it out and diagnose. Any help would be much appreciated.