Freezer only reaches 20 degrees. Fridge stays at 37 degrees. Hear fan and feel cool air blowing through the vents in the freezer. Fan in back underneath is running. No frost/ice buildup. Coils are clean. Compressor runs smooth, but is very warm to the touch.
Does the compressor and it’s fan run all the time, other than when it goes into a defrost cycle?
If yes then remove the cover in the freezer so you can inspect the evaporator coils,
They should have a fairly even coating of frost on them.
Be sure to do this after the compressor has run for a coupe hours. If you do it during or shortly after a defrost cycle you will come to the wrong conclusion.
If there is only frost in one area (usually where the freon enters the coils) or it is patchy you have a sealed system problem.