Several factors could prevent a refrigerator from cooling, such as the door not sealing properly. If the door gaskets have rusted, warped or come loose, the door will not form the seal needed to maintain the proper temperature.
Another common reason for a refrigerator failing to get cold is that the temperature control setting has been adjusted. Turning the control one number higher will help to determine if this is the problem. Other things to check include making sure it is kicking into defrost mode when necessary. Most refrigerators models can be manually put into defrost mode by pushing the switch that controls the light when the door opens five times quickly. Users should also check to make sure the condenser on the bottom or back of fridge is clean and free of debris. These can be cleaned easily with a wire brush or vacuum.