2007 Kenmore 596.66252400 : Temperature variation (37F to 52F)

Hello everyone and thanks for your help.

I have a 2007 Kenmore 596.66252400 with the freezer at the bottom and no ice maker. Recently, I begun to have problems with it and someone reffered me to this forum to ask help.

Symptoms

• The temperature vary day to day. For example, last saturday the temperature was around 3*C (37F) , and today it was at 11*C (52F) when I came back home.
• Last week, I tried to defrost it: I left it unplugged for around 5 hours thinking it would solve the problem. It worked for almost a week, but the problem came back
• The compressor will start if I move the temperature dial of the freezer and I can feel cold air blowing in the freezer and the refrigerator
• I cleaned the bottom-front coils... I don't see any back coil (there's a metal sheet and it seems I can't remove it)

If anybody has a clue about what's going on? I search for an answer since almost 2 weeks now, but I can't find any solution for my particular problem.

Thanks again!