samsung fridge freezer model SR-L629EV s/no 602041AT500135 D?

My freezer is not working. It keeps making ice in the back of the fridge and doesnt send any air to the freezer. I have defrosted throughly and started again and the freezer still is not working showing temp of -4 and the fridge as +5. The fan is working. and the fridge part is fine too. In the fridge area it keeps freezing food in the vegetable tray. Somebody said it might have a weak sensor as its not telling the fridge to defrost. I am confused as the temperture are being read correctly. please help what part should i try changing. many thanks