I have a Rheem classic hvac. The outside unit has ice on inside walls of heat pump as well as on the top. A service guy replaced a board & it still is freezing. He changed a setting on it he said & it is still freezing. Also, the furnace runs all the time even when it gets to the desired temp. This has been going on for two weeks & I am frustrated because I can't get it fixed. Help me. Thans