More than likely, your 5 yr old dehumidier may not be a "low temp" operation model.  Even if it was designed for low temp operation, many manufacturers' units can still only operate correctly (not freeze up) if the temp is above 40-50 degree range.  I've only seen one or two units so far that advertise that they can operate down in the higher 30's.
                 Dave Lindler
                
 January 2007