I had the same problem on a one year old Summit FF874W, zero in the freezer, 50 in the fridge, clean coils etc, but after reading in this thread I got an idea!
I checked the fan, and it was not running, so I thumped the back of the inside of the freezer with my palm over where the fan is and the fan started to go then scraped to a stop.

So I took off the 4 screws holding the panel in place, and removed the panel with the fan attached.
That's when I discovered the problem :)

The fan was screwed to a metal bracket which in turn was screwed to the back of the panel, I noticed the fan bracket was loose and the fan just fell out, I noticed the screw heads were broken and that allowed the fan to shift a bit and get jammed.

So I replaced both screws with new stronger ones, and it works fine now.

Your refridgerator gets its cold air from the freezer by way of a fan that transfers air past the freezer coils to the refridgerator. If the fan isnt working the refridgerator will not get cold. I your coils in the freezer are freezing up this will also stop the flow of air to the refridgerator. The first thing to check is the fan.

My freezer is working, but about a week ago I noticed the fridge getting warmer. On Friday it stopped cooling completely in the fridge and became very warm inside. Everything ended up spoiling. I unplgged the whole unit and let it defrost for a full day. The little holes on the top of the fridge compartment in the back leading up to the freezer were frozen solid and I waited for them to thaw before starting it back up. I have plugged it back in and the freezer is still working, but the fridge still is not. it's not even making any noise at all. Can anyone please tell me what I need to replace? I cannot afford a new fridge and need to repair this one. Please talk to me in layman's terms so I can figure it out myself. Thanks!