Why won't my refrigerator cool?

I have a Fridgidaire side by side. I bought it brand new in August 2007. About a week ago, the freezer quit freezing and the refrigerator side wasn't cooling at all. Repairman replaced a timing unit. Then he replaced the circulating fan. The freezer cools like a refrigerator, and the refrigerator doesn't get cool at all. He said the circulating fan isn't kicking in for some reason. All of the wiring harnesses have also been replaced. What else can be causing this problem?