Idler or Tensioner?

1998 Taurus, V6,3L, OHV. Need to replace the alternator and was wondering which pulley loosens the serpentine belt - the idler or tensioner ?? I’ve tried both, and was wondering if anyone has any tricks because instead of “swinging up” and allowing the belt to be taken off, both just loosen up and go absolutely no where - regardless of which way I turn either one of them Any I missing something here ??

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