Freezer switching off on Hotpoint Iced Diamond...

Question

Hi. I have a Hotpoint Iced Diamond RFA5IP fridge freezer and I find when the room temperature falls to below approx 6 degrees celsius (43 farenheit) the appliance switches itself off and the freezer defrosts. I often come back to find that it has switched itself back on again and the red light (high temperature) is lit. I have altered the temperature dial and tried it at 1, 3 and 5 (it goes from 1 to 5) but this appears to make no difference. I would appreciate your advice on what to do. Many thanks.