I have an 87 635 csi. To add freon to my ac system, do I use the valve by the sight glass located at the passenger headlight? There is another valve closer to the rear of the engine, but this tubing looks much thicker. I'm figuring this is the high pressure line. While the sight glass tubing is thinner. My Bentley doesn't identify the proper valve. I'm not enough of a mechanic to do this without guidance. Thanks in advance.
PS I have a rear ended 86 535i if anyone wants some components.