You can buy refill bottle of freon with gauge and hose for about $15.
I did it last season on E. It was easier there, since E has AC pressure display on the climate console, but adding single bottle is not going to harm anything. If that doesn't work, than you take it to the shop.
Amazing thing, that freon on my E drained to absolute 0, but after refilling it hold for the rest of the season. Evidently something opened and closed on its own. Time to check it for this summer.
I agree, you may want to evacuate the system in order to remove all the impurities that affect the AC performnace. Since you will be evacuating the system, you will need to add some oil, too. It makes a huge performance difference having a system with no water/impurities in it. It cools very fast and gets as cold as the system can..
You will need to take it to some AC place where they have the machine to do it.
2005 ML 500
Black, 18" AMG Wheels, 285/60R18 Yokohama Geolander HTS + Bi-Xenons(+ Drew's e-code mod, though the reflectors rusted off and do not give out much light anymore), Yakima roof bars, Akebono pads all around. Former vehicle 2001 ML 320 with 108K miles, when traded, and a large repair/defect history. After all these years of owning my current 2005 ML 500, it is a major unreliable vehicle with a very large/expensive repair/defect history and has been like this since brand new.
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