Dehumidifiers work on the same principle as refrigerators and air conditioners. They have a cooling system that refrigerates the air entering the unit. The moisture in the air condenses on the cold coils and drips into a holding tank. The cold air is then passed over a warm set of coils and reheated to just a little over room temperature. For more information, see the "How things Work" section.
Because the room is too cool. Because dehumidifiers remove moisture from the air by chilling a set of coils and allowing the moisture in the air to condense on them. If the room temperature is too cold, the moisture can freeze. To prevent ice-up, you may need to either raise the dehumidifier to a higher (warmer) location or increase the temperature of the room.
When it's full. You don't need to empty the reservoir before it's full as long as there's a safety shut-off for when the unit is full. Most units have one.
Usually. Most dehumidifier water containers have a sealed outlet on them to which you can attach a garden hose. Sometimes you need to remove the plastic in the center of the outlet before you hook up the hose. If you need to stop up the hole later, you can purchase a threaded hose cap at any hardware store.
We suggest that you buy a separate, good-quality hygrometer to determine the actual moisture content of the air in the room you want to control. Then, with a bit of experimentation, you can set the humidistat on the dehumidifier so that it cycles off when it reaches the humidity level you want to maintain.
Usually no. If your dehumidifier is running constantly and the water container is not filling up at least once a day, there may be something wrong with the dehumidifier. But if the unit runs constantly and the water container has to be emptied daily, there's just a lot of humidity in the room and the dehumidifier is doing what it's supposed to do.