A5 Compressor "Port"

[CadillacFlashback]

Can anyone tell me what this large "port" in the body of the A5 compressor (circled in blue) is for? 

[dadscad]

Looks like a pressure relief valve. If for some reason, the system becomes over pressurized, an over charge of refrigerant or maybe a stopped up dryer or expansion valve, etc. It will relieve the high side pressure. That would save possible rupture of other components, hoses or coils.

[Scot Minesinger]

Or it could be oil

[Jon S]

Or it could be oil

That was my thought . . .

[CadillacFlashback]

Or it could be oil

The manuals show that oil is added through the bottom

["Cadillac Kid" Greg Surfas 15364]

Scott,
Pressure relief valve assembly "wins" by a landslide.
Greg Surfas

[John Washburn CLC 1067 Sadly deceased.]

Yep,

The Master Parts List agrees also. 54.1153 calls it "Pressure Relief Air Conditioning Compressor Valve Assembly".

The Johnny