Adding 134a-- Which port?

I have a friend that owns a 1998 Century(the last body-style) and his air-conditioner is blowing lukewarm.

I have extra refrigerant left from refilling my neon, and that was a straight-forward process, but this Buick is another matter!

The ports seem to be located around the driver's shock tower, but which should I add it to? There was one that I recall was nestled into the firewall, on a more flexible line, and there were two that lived lower in this spagetti-like mass of things.

Which do I add the refrigerant to? Any images to help me out? He doesn't own a service manual for the vehicle!

Thanks in advance!

I believe the fitting will only fit one of two ports.