help adding freon to 2004 malibu

I am trying to add freon to a 2004 malibu, I have two sliver lines pretty close to each other but I am not sure which line to add the freon to, one line is a little bigger than the other, and they both have black screw on caps. any assistance is greatly appreciated! :)

If you got one of those do-it-yourself charging kits, the hose will fit on only one fitting on the car. The car ports are different sizes to prevent you from attaching a can of freon to the high pressure line, possibly exploding the can in your face. The low pressure line (not fitting) will usually be larger in diameter. Always add freon to the low presure side!

technical knit picking...is it freon? I thought freon was dichlorofluromethane.
the 2004 uses tetrafluoromethane
It is also good to wear some eye protection also

Using the word "freon" as a generic term for refrigerant. R-134A would be a more correct term.

The real issue is missing here " just" adding freon is incorrect, how do you know you are not overfilling the system, this will kill performance, it should be evacuated, leak tested and charged with the proper fill amt.