Westinghouse/Gaggenau fridge - freezer

[Melanie]

Hi,
If anyone can help us figure out what is going on with our fridge.
We have a Gaggenau SK 535-2 62/1 which i think was made by Westinghouse?
The fridge is not staying cool because the freezer is not (regularly) defrosting when set at -15, i think the vents get blocked up so cool air stops flowing into the fridge? But it defrosts sometimes! and also when i turn the freezer right (-20) down is continues to ice up but the fridge stays cool. Which part do you think is the one that needs replacing...first! We bought it cheap at an auction and think we now why now
Any help much appreciated.

[tonto33]

defrost problem need to check defrost heater and defrost sensor