97 80 Series - AC Compressor Valve Port

[LaffTown]

Question for y'all. See attached photos of the suction valve manifold that I will be migrating over to a new Denso compressor. I see there is a port with a fitting installed. I am curious if anyone might know the function for that? Looks to me like it could be some pressure release passage. I see nothing in the FSM on this. Nor has google shown any threads on Mud or elsewhere.

Thanks in advance.