I think you guys may be confusing 'integral gain' and 'integral sum'. Setting Ki to 0 will not set the integral contribution to zero, at least in the vast majority of PID implementations. I know that all the books show the integral term as:
Ki * INTGL(e)dt, which infers that the integral sum is multiplied by the gain. In my experience, most PID loop integral terms act more like:
INTGL(Ki*e)dt.
Mathematically I believe they are equivalent. But in practice they are not. Setting Ki to 0 will simply cause the integral sum to hold at it's last level.
Having said that, I don't know why you would both set Ki to zero AND disable the rung. That doesn't make much sense to me.
However, I can think of cases where you would keep the rung enabled and set Ki to zero. I do alot of web applications. I can't always guarantee that the web is fully under control when I start. However, I want to have some correction to 'keep me in the ballpark' when I start. So I will operate with the integral effectively disabled and operate in proportional control only until i am confident I have full control of the system. This prevents excessive integral wind-up.
Keith