I have a bell upright freezer model tff 654w. The red light keeps coming on and frost is forming at the back of the freezer. We have checked the temp and it does not seem to be getting down to -12 only going down to around - 8 or -9. We have defrosted it and it is forming ice even after 3 days. What could be the problem. It's is only 2 years old. It is in the garage which is a bit warm but no warmer than the house.