The first problem two days ago was that both the fridge and freezer stopped cooling. Emptied both and cleaned dust from bottom coils. Adjusted temp controls to coldest settings. Temp in Freezer went down to -15 but fridge stayed 39. Checked behind panel inside freezer - no ice buildup is visible, just a very light frost on the coils but the temp went up to 50 degrees in there so I'm not sure if there used to be ice back there. The evaporator fan (I think that's what it's called) is running constantly. Some cold air flows out of the vent in the top of the refrigerator section but if you open the freezer door, a lot more cold air comes through the vent into the fridge. I can't figure out if this model has a manual way to put it into defrost mode or if there is a return air vent somewhere in the fridge that is clogged. The only other vent I can find is about 1/3 of the way up the inside wall of the fridge and it appears to be perfectly clear. What do I check next and how do I check it? Any ideas would be appreciated.