This can be a pesky problem, and may mean you need to replace the refrigerator. However, there are a few things you can check on your own before you shell out several hundred dollars for a new unit.
You’ll likely notice is that your refrigerator isn’t keeping things cool. This is relatively easy to check, but to get the most accurate reading of the cooler temperature, stick a thermometer in a glass of water (necessary to equalize the temperature) and put it in the refrigerator. After 12 hours, the temperature should be no higher than 43 degrees F. After 24 hours, it should be in the low 20’s to high 30’s maximum.
If you can’t maintain these temperatures, the cooling unit is bad and should be replaced or rebuilt.