It sounds as if you are not an experinced refrigeration guy so it's important that I warn you.

Do NOT try to charge through the high side port! This can result in can explosion!

If you don't know how to identify the low side port, then stop, do some research and KNOW what you're doing.

You should use manifold gauges on this car. On some American cars the fittings are fool proofed to prevent incorrect connection. Your MB, however, has the same size ports on low and high.

I would strongly recommend that you do some reading and learn the principles of refrigeration, get correct equipment and be SURE of what you're doing before proceeding.

I have thought a few times that if any of our mshop friends were to get hurt or worse, we would probably never know about it, at least not in this lifetime. We would just stop seeing their posts.

Be safe,