Motors Can someone tell me which port?

the AC on my moms 1998 GMC Safari started only blowing hot airlast year right at the end of summer. we didn't do anything about it because times were tight and it would be 40 degrees in a month or two anyway, but now it's 100 in the shade.

i picked up a recharge kit from wal-mart (Interdynamics Arctic Freeze AF-22) with a pressure gauge on the hose. From what i read, if i connect the hose while the engine is running and the gauge pegs in the red i'm gonna shut down everything and back away slowly, there is a plug in the system and handling high-pressure lines is out of my league. if i connect the hose while everything is running and the pressure is low i'm going to slowly add R-134A until it's in the zone marked on the gauge.

according to the video on interdynamics website, it looks like i am right, and the silver can is the accumulator. can anyone tell me for sure either way? there is a warning on the can saying if i tap into the high-side line the can could explode, and i don't want to find out if they are serious or not