Fridge freezers usually have 2 separate cooling systems, one for each cabinet. So probably a fault in one system. Might be simply a thermostat fault (if a sudden failure) but if its got gradually worse might be a sign of a fault in the gas circuit, loss of gas or a faulty compressor (although they normally last years) Nothing you can do for a gas circuit fault, all sealed etc. Check the thermostat, then get out a service engineer as I had to do! New compressor around £70 fitted some years ago on my electrolux, but probably a common bought in unit in most freezers.
Andy
January 2007