A dehumidifier is built with an evaporator that is supposed to condense the moisture in the air and let it drip either in the condensate bucket, or leave through the built-in pump. Most dehumidifiers are built to work even when temperatures drop under 70oF. When temperatures drop below this level, frost may form on the unit’s evaporator and render it functionless. Something else that could be the cause of your dehumidifier freezing up is when the fan motor is not turning fast enough. You can reduce the freezing up by moving your unit to a slightly warmer area or by you could seek a solution to the fan motor problem. If you are using the unit in your basement, try looking for units that highly efficient (Check our review about dehumidifier for basement)