Refrigerator dampers allow cold air to flow from the freezer to the refrigerator. A stuck damper restricts that airflow, causing the air in the refrigerator to become warm -- sometimes too warm to keep the food fresh. Other features of a refrigerator's cooling system might also be affecting the damper's operation, so it may not be an isolated problem. For this reason, consider hiring a professional to diagnose and repair the problem.
Cold air is produced in the freezer as liquid refrigerant passes through the evaporator coils and changes into gas. This process causes the surface of the evaporator coils to become extremely cold. A circulation fan blows air over the coils and through a vent into the refrigerator. Within the vent is a damper. The damper is a small flap that controls the flow of air from the freezer to the refrigerator. It is usually found in the top of the fridge or on the back panel near the top. The damper is controlled by a thermostat, which triggers it to open and close depending on the temperature of the air in the refrigerator. In some cases, it can be triggered by a timer, or a combination of the two.
Although a variety of things can cause cooling issues in your refrigerator, it's easy to see whether the damper could be the problem -- simply stick your hand in front of the vent. If you can't feel any cool air flowing into the fridge, and you know the evaporator fan is working, the damper is likely stuck in the closed position. If the damper has a removable vent protecting the damper flap, remove the vent and see if you can manually move the damper. If not, you might have to call a professional to repair it.
You might think the stuck damper is causing the cooling problem, but if you have not verified that, there might be a problem with the evaporator coils instead. Check the inside of your freezer. If you see ice and frost building up on the walls, this is a sign that your self-defrost system is not working and that ice is also collecting on the surface of the evaporator coils. Too much ice limits the flow of air over the coils as produced by the circulation fan. As a result, there will be much less cool air flowing into the refrigerator through the damper.
Replacing the Damper
Some refrigerators have dampers that are connected to the refrigerator's electrical system -- including the timer and thermostat. A professional should replace or repair these. Not only are they harder to repair, but because they are controlled by an external thermostat they will malfunction if the thermostat malfunctions. If you are replacing the damper, consider a self-contained unit. These have their own power source and thermostat, and are much more easily replaced if broken.