we service two seperate sites with 75 ton mcqauy rps style units that will rapid cycle the supply fan contactors to death,weve swaped out ribbon cables, mc boards,output boards, relays you name it ,the problem always comes back,may go away for up to 9 months,but will still return.one site has vav style systems the other is constant volume,several units at both sites with only one at each acting up. michrotec contol system both vintage around 1996.anyone out there have or solved this problem?