@ MICKEY and bce123, So I put the JSR instructions in the main ladder (LAD2) to jump to the main air dryer program in LAD 3 and PID control in LAD 4. The air dryer program cycle is about 3 hours. Will the PID loop be executed repeatedly without waiting for the main program to be done?
@L5K_Edit, I did change the PID output indirectly to an N file. We don't have an MANUAL/AUTO mode for this air dryer system; however, there is a manual valve for the heat exchanger.