I have a 220 ver 4.02,SC36 cell, 4200 ppm salt, voltage email@example.comA (typ). The cell gets coated with white salt after a few days. I replaced the cell and still have the problem. The book said the polarity needs to change every 4 hrs. I put a voltmeter on the output tabs on the control unit (the ones that go to the cell) and the voltage never changes polarity. I know that the display ON or OFF has a period that comes and goes to indicate a polarity change but the out put voltage does not change polarity. I can do a forced polarity change and the output polarity does not change.Should the meter change polarity is the 1 st question and would the problem be in the control module or the power supply unit?