Fridge / Freezer please help

Hi there i may not have discribed the issues that i am having with my seimens fridge freezer 50/50 the fridge part of the f/f works and has a temp of 3c, you can hear a fan running in the freezer half,when you open the door of the freezer the fan seems to stop although the freezer half is cold it is not freezing the contents i have tried switching it of for 12hours but this has not made any differance, you can clearly hear the motor cutting in and out as it should, thanks for any comments as im at a bit of a loss and am wondering if this is in fact repairable kind regards Gary