An evaporative cooler is a box-shaped appliance with one or more porous surfaces that enable air to pass through. A fan inside the unit pulls outside air through the sides and into the house. To produce cool air, each porous side is fitted with a pad of water-absorbing material. Water is stored in a pan at the bottom of the cooler and a small pump lifts the water to the top of each side.
To effectively cool your home, each pad needs to remain damp, but not soaked. Dampness creates the most evaporation and, therefore, the most cooling. The amount of water the pump moves may need to be adjusted from time to time to properly dampen the pads.