How do I setup my P Series control for On/Off control?

You need to set the Primary Output Proportioning Band Pb_P to 0.0.  This parameter is in the Setup Mode.  Once this is set another parameter will be available in the setup mode that may be useful for your application.  It is the Primary Output ON/OFF Differential  diFP.  This sets the differential between ON and OFF and can be adjusted between 0.1% and 10.0 % of the span of the control.

How to navigate to the Setup Mode