Whats the problem?

I have a fisher and paykel fridge C270 .When you look inside to the top right hand corner when 2 pipes enter to join a "cold"back plate,only the top right hand corner is cold and eventually builds up to be a large block of ice,what has happened is it worth fixing,the fridge otherwise looks perfect.I have defrosted and dried out but the same happens after a few days.Many thanks for any replies.