Games : Activate clock only when command block output is true

I'm trying to activate a clock when a player looks south. I got the command for it, but when I try to make a comparator clock even if I'm not looking south the comparator clock is still going, so how do I make a clock that will only activate when the command block output is true. I'm using a comparator to test if it is true, then a repeater to extend to 16 redstone then with that 16 redstone I use it to activate a comparator clock but when I'm not looking south the very 1st comparator doesn't turn off.