Refrigerator Won't Get Cold

The refrigerator won’t get cold. The freezer works fine. Following a tip we found online somewhere, I vacuumed out underneath the fridge and poured hot water in two vents at the bottom of the fridge (behind the vegetable crisper). This worked for a few weeks, but not any ore. A friend said that the defrost timer may be broken, but I can’t figure out how to take anything apart in this unit.

HOward