Correct me if I am wrong. The fans will run sometimes, the fresh food is freezing at the bottom, the freezer sometimes defrosts completely, the fresh food fan doesnít seem to be running and the turbo light stays on all the time.
I donít think it is going to be the user interface (control with turbo cool light). But you can try disconnecting the user interface control. I believe if you unplug this control the main board is going to run on a default mode that should cool the fresh food to 37 degrees and freezer to 0.
You will not feel a lot of air coming out the duct into the fresh food section in fact it can be hard to tell if the fan is running or not. It is not going to move as much air as the other fans.
The damper could be staying closed but that wouldnít explain the fan motor issues as well as the freezer defrosting. It could however cause the bottom of the fresh food to freeze. Never the less you can take the air duck down so that you can see the air duck inside the air duct. You do this by removing the top shelf (maybe the next one as well) and popping off the cover at the top where the light is to access screws. Once off closed the door and wait three minutes. Then open the door and look at the damper, it should be open. Then after three minutes the damper should close and if you press the door switch it should open again. This will confirm that the damper will open and close.
Are you sure the fan next to the compressor is running? I have seen them run slow and not move enough air to cool the compressor. If the fan next to the compressor isnít running or running slow the compressor can be short cycling possibly causing all your problems (other than the turbo cool light).
The problem I see with the fan motor test you did is by the time you did the test the fans had started running. If you had did the test before they came on you would know if the board was calling for the fans to be on or not. If you were getting voltage to the motor and it wasnít running then you would know the fan was bad (or vice versa) however if the fan were running you would expect the voltage to be correct especially if it were running fast. I can tell you that if the door is opened for more than three minutes the fan is supposed to come on and if not you need to know if the board is sending voltage or not.
There is one more thing you can do to clue us in as to what is going on is to remove the back wall of the freezer with it running and describe what you see. Is there heavy frost build up on the coils that could block airflow? Is there light frost along the entire coils?