A/C service port

On my 1999 4-door Tahoe (5.7 V8, 4x4), can anyone tell me where the low-side service port is for the A/C? Under the hood, passenger or driver side, etc.? I found a green-capped valve marked as an EVAP port, but I don't know if that's different. Thanks!

Shodid...pop ur hood...face ur truck...extend ur right arm out...u should touch ur compressor...the last pulley on right(on top)...ur a/c ports right on top....one port is facing u...and one port is facing up...both has black caps...the one thats pointing at u is the one ur a/c line hooks up to!! dont worry the a/c line only fits one...u cant mess up!!! if u have just the front a/c u just need 3 12oz cans and 8oz of oil... and if u have rear a/c u need 64oz thats bout 5.5 cans but i'll do 5 to make sure i dont over do it and 11oz of oil !! this is if its bone dry!

http://napabeltshose.com/downloads/download_common.cfm?file=NapaCapacityGuide2-8-05.pdf&folder=news&view=napa_hc