Whirlpool freezer not getting cold enough

I have a Whirlpool freezer (model EV171NYMS03) that is not getting cold enough. It is currently below freezing, but just barely. I replaced the fan motor earlier and that is still running. When I took everything out and looked at it this morning, I noticed a large amount of frost on the vents near the bottom of the freezer on the inside. I melted the ice/frost with some warm water and also removed the back panel and noticed that the evaporator coils were also covered with ice. I let everything thaw out with the help of some more warm water and put everything back together about an hour later.

Now several hours have passed and it is still hovering just below freezing. Is there anything else I should look for?