CONNECTION TO RECHARGE THE AC W/REFRIGERANT

Hello, I have a 1998 pontiac firebird w/ a 3800 series II V6, 78,000 miles. I have a R134A a/c recharge kit, but I cannot find the low air connection to hook the hose up to. I found a connection that the shop manual says to use, however it has a pressure switch connected to it, that turns the compressor on and off, so I cannot remove that or the compressor does not work. The only other correct size connection I have been able to find is directly located on the side of the accumulator, it has a black cap on it. But I do not think this is where I am suppose to recharge it at, there is also another connection next to where the low air hose goes into the condensor, however it is too big for the hose plug. Can anybody PLEASE help me find the correct connection to use?