Low Pressure AC Port location?

[bleu7]

Hello, I have searched for this question in various ways and have received no solution,

so I'd like to know where my Low Pressure AC Port location is, in order to recharge my AC?

my old sentra had a clear blue cap on it, but in my trailblazer i see two seperate black tops one on the cylinder by the back of the engine bay on the passenger side and one appears to be on a line that goes into the radiator...

i am pretty sure that it is the black cap on the cylinder, but would like some reassurance....

thanks in advance

 

[AV8ER]

Its the one in the back of the engine bay on the passenger side on the silver cylinder

 

[HARDTRAILZ]

Reminds me to recharge mine. I got the stuff, but never remember to do it until I am driving and realize it wont blow very cold.