AC recharge question.

I am going to recharge the AC in my '90 750iL before doing any troubleshooting. First, I have a possibly stupid question. My car still uses R12. I don't want to convert it. The only port I see is by the passenger side intake plenum and has a red cap on it. Red usually means high pressure side, but it's the only one I see. Is that the low pressure port with a wrong cap on it? If not, where is the low pressure port? Thanks guys.

AC recharge question.