Warm fresh food section

Hi,

I have a GE Side-by-Side Freezer and it is not cooling in the fresh food section and is cool in the freezer. I have had a problem in the past with this fridge with the same problem, and this was about a year ago. The first time I followed this guide and I found the Defrost Heater was bad. So I ordered the part and an upper thermostat(it was cheap and I did not want to come back to this problem) and replaced them. When I did this the it began operating normally. About a month ago, it started having the same problem. So I took the back panel off expecting the Defrost Heater to have failed again. Instead I noticed it was actually in the process of running at the time. So I placed the panel back on and and came back the next day. Still having the same problem, except that this time there was a definite difference than before. The bottom third of the evaporator coils were not covered in ice but the rest were. To my thinking the defrost heater could not be non-functional if it is running periodically. Here are my questions:
Is the timer bad, which to my understanding is on the board, and the problem could be that it is not leaving it on long enough?
Or is the heater unit possibly bad again?
Could the problem be that the thermostat is bad?
Do you have any suggestions on how to fix it?
I appreciate your help from before and I look forward to your help now.

Pull the cover off the motherboard in the back. Unplug fridg and unplug the three pin,gray power connector and place a wire jumper between the mating
board pins labled line and comp. Plug in fridg and check the evaporator after a period of time. If it gets fully frozen, you may have freezer thermistor problems. If not, you have refrigeration problems.

When I put the jumper wire on, how long do you want me to leave it on for? If it is the thermistor, is it that difficult to change?

The compressor should start when you plug in the fridg. If so, pull the jumper off and plug the connector back in the board.