Fridge temperature at 50F instead of expected ~37F. Took cover off freezer to check for ice in the evaporator. No ice. Fan operational. Noticed drain plug was clogged. Cleaned out drain plug. Also removed front grill and noticed it was thick with dust. Cleaned grill and coils. I put everything back and power cycled it. But after a few hours it's back to 50F, but I do feel a bit of cold air from the diffuser. Will check again in 24hrs. Q: Could it be the air diffuser? How hard is it to replace it? How can I tell if the diffuser is bad? Thanks.