I'm not sure where else your low pressure port could be, but I have the same 2nd high-pressure port behind the driver's seat there, so I'd feel pretty confident in saying that both of the red-caps you've found are the high-pressure ports.

Also, the low-pressure cap is likely black on your vehicle and blends in pretty well. That blue cap, which is way larger than the original one, was from the r-134a adapter I screwed onto my vehicle.