It is not a difficult DIY. They make it 'idiot proof' these days when you buy the kit. Many years ago people hooked up the then R12 Freon to the high side, the nipples were the same and blew themselves up, by blowing the can up when the compressor started pumping IN TO the new can. Now either the low side nipple is different or the high side is not there. Follow the instructions with the kit of R134, you should have no problem.
The low pressure service gauge port valve is located on the manifold of the A/C compressor manifold and tube assembly at the A/C compressor. Item 5 in this image ...click on the image to see it
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