1987 Chevy k10 350 ac help!!!!

[jtstrick38]

I am going through ac on my 1987 Chevy k10. After replacing major parts found I had hard line that needed replaced. Bought new line and new line has extra fitting that previous line did not have. If anyone can tell me what goes into this fitting? I found brass plug that seems to fit hole. Not sure if it’s relief valve or pressure switch?

 

[jtstrick38]

Here is the brass fitting I found them at seems to fit into extra fitting.

 

[TX87R10]

I am going through ac on my 1987 Chevy k10. After replacing major parts found I had hard line that needed replaced. Bought new line and new line has extra fitting that previous line did not have. If anyone can tell me what goes into this fitting? I found brass plug that seems to fit hole. Not sure if it’s relief valve or pressure switch?

Iirc Summit sold me this same part. I ended up returning it and fixing valve stem in the one I had.