Background
If fresh foods are stored in areas with low levels of moisture in the surrounding air, they are prone to drying out and going bad. Unfortunately, the traditional refrigerator design does not encourage moisture production. This is because the evaporator, which is responsible for sucking out heat, is typically located in the freezer. A fan circulates the cold air a condenser produces into the fresh foods sections, but not before many of the water molecules in the air freeze to the surface of the condenser. As a result, the air in the fresh-foods section is not very moist. Moisture control systems combat this problem by introducing air from the surrounding environment into the refrigerators.
Bringing In Outside Air
Refrigerator moisture control systems allow external, non-refrigerated air to flow into the fresh foods sections of refrigerators. The systems accomplish this via passageways or pipes, which can be located on the side panels, back panels, tops or doors of moisture control refrigerators. To regulate the amount of external air flowing into refrigerators, moisture control systems utilize louvers or shutters, which can open and close to let in more or less air.
Manual vs. Automatic
Moisture control systems in refrigerators can have one of two primary modes of operation -- manual or automatic. To operate a manual moisture control system, you turn a dial, lever or push a button, which triggers the air-regulating shutters to open wider or close tighter. The precise mechanism for doing this will vary from model to model.
With an automatic moisture-control system, there is typically a push-button interface on the inside or outside of the refrigerator, which allows you to select a specific moisture level. Unlike with a manual system, the automatic system uses a sensor to detect the amount of the moisture in the air. The system then moves a motorized damper to increase or decrease the flow of external air as needed to maintain the selected setting.
Filtering
To prevent foreign particles like airborne dust and dirt from entering the passageway of a refrigerator's moisture control system, manufacturers include filters at the passageway entrances. The filters catch particulate matter before it is able to flow into the fridge.