By default, energizing the Interlock Signal Pin 4 on a Control Port on the Downstream side of a ConveyLinx Module will cause that zone to accumulate an item when it arrives on the zone sensor. You get the same result if you energize the Local Accumulate Signal on Pin 3. So if all you want to do is accumulate a zone, which signal should you use and does it make any difference? The answer is yes it can make a difference

What happens if you use Pin 3 when you should use Pin 4?

Suppose you want to control the release of multiple items by toggling the Pin 3 signal. After you release the first one, you will get an Arrival Jam because the module is looking for the Pin 4 signal to be energized in order to “confirm the downstream arrival” of the item. So, by using Pin 3 in this case, you will have to wait the Jam Time plus the Auto Clear Time between release of each item.
Downstream Control Port Pin 3 is ON and Carton 1 accumulates when it arrives
When Pin 3 is turned OFF, Zone 1 will run to convey Carton 1 on downstream
When Carton 1 clears PE1, Pin 3 signal is turned back ON. Because Pin 3 is ON, Carton 2 will stop upon arrival at PE1 however because there is no signal to Pin 4 to indicate arrival downstream, Zone 1 will generate an Arrival Jam !!!