Thermistor or Thermostat?

Refrigerator & Freezer Repair
1

Brand:Whirlpool
Model Number:WRT138FZDW00
Main Symptom:Freezer not freezing
What happens & when: Ice forms inside the freezer on the right side. I opened it up to find a solid block of ice where the thermistor or thermostat is mounted to the copper pipe.

Error Code (if any):
Parts or tests already tried: The thermostat you sent does not go in this freezer. The guy I spoke with today (Mike) said this model uses a thermistor. I have pictures if anyone can help me figure out why this thing isn’t working right. The stuff gets cold and sometimes freezes but nothing stays frozen and that area always ices up. After getting the cover off I understand why. There was solid ice all over that entire right side about six inches high and wide and at least an inch thick.
Photos / video link:

2

Have you or can you check the resistance readings of that thermistor and the heating element?

3

I don’t know how to do that. My brother tried to help me understand a multimeter, but they mystify me. I already put the back cover back on and turned the machine back on so as to not lose any food.