1992 Buick Lesabre recharge

Air Conditioning problem
1992 Buick Lesabre 6 cyl Front Wheel Drive Automatic
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how do i recharge my ac? i know i need to attach recharge kit to my low pressure line but dont know where that is and i dont want to attach to high pressure line on accident. I have found two areas to connect to one is like a tire with a pressure relief valve and the other does not have that valve. If one of these are the one i want please tell me which one is the low pressure and if both are wrong where should i look to locate what i am looking for?

thanks