Refrigerator Won't Stay Cold?

My Kenmore model 596.67272790 bottom freezer stays cold, but top refrigerator gets warm after about a week. Everything has been cleaned out and door seals are in place. The blower fan runs. It seems like the unit is not defrosting and freezing up (bottom unit behind panel in freezer section). I defrost it, but in a week the top fridge gets warm again (no cool air flow from freezer). Bottom freezer never gets warm. Fridge kicks on and off with no problems. No issues at all until bottom coils freeze up again, then I defrost them. All is good for only a week or so.

By Glenn