I have an old Frigidaire freezer (FV1241) (upright) which seems to work perfectly well.There are 3 lights, red, amber and green and the red and amber ones come on when I switch it on, and it gets very cold. But the red light doesn't go out and the green light doesn't come on even when the freezer has been on for 24 hours. Is it likely that it's not working properly?