One month later and it's finally hot enough to get me to go outside and do this. Found a sight glass under the intercooler intake, and found a port on the top of the compressor. The port has a black cap and an "S" stamped on it. I'm guessing since this is on the top, that it's not the right port. Can't find a blue-capped port anywhere.

Do I have the right one? Where do I need to look?

1991 Mitsubishi Pajero XP TD LWB family hauler.