Second, running the fan constantly in a humid climate will greatly reduce the air conditioner dehumidification. An air conditioner can only remove moisture when the outdoor compressor is operating. When the compressor turns off after running for half an hour, the cold indoor evaporator coil is still wet. If the fan goes off, the condensate line drains. But if the fan is left on, the water on the fan coil and some of what is in the drain pan will be re-evaporated back into the air stream and blown back into the house. This means that much of the air conditioner moisture removal potential will be lost. In a humid climate, that can be a huge problem.