jacrouch, I am sorry to inform you that that is not the type vacuum guage or pump which are used on the AC part of your car....
I asked the question on a hunch.... I thought maybe you had purchased one of the venturi type which run off the air from an air compressor... about $35 ... which is also not appropriate for this task.... Even used the type vacuum pump you need for evacuating the AC system is usually over $200.

My first advise may sound harsh... but you can ignore it and go to the second after you read it.... You are over your head on this part of your car's equipment problems. The amount of tools and knowledge you would need to acquire and apply Fast is huge. And not a small part of the problem is that there is a Safety Issue. AC involves serious stuff under pressure... which can explode and maim you... read Blind /Disfigure you. I was very lucky in the early 70's when I hooked up a can of R12 to the wrong side of the system and caught my mistake before it exploded in my face.... There are not the warnings which you have come to expect dealing with consumer goods.... they figure you will not be working on these things unless you already know the safety rules....and the function of the parts without markings on them.

I consult three manuals on AC... one is the Factory Mercedes AC manual , one a strickly Automotive AC manual and also a huge HVAC text with a section on automotive AC. They are strewn with warnings throughout.

You should at least find a copy of the Factory Mercedes AC manual... they are very specific in how they want things done... but then you will also need to purchase a set of guages for whatever referigerant you have in your system... which you will need to identify by the style valve installed. Then , to buy R12 cheaply if you need it you will need to take the online openbook epa test.... 608 or 609 ... do a search , plenty of info posted..... then you have to understand what electrical systems control your AC in order to by pass them one at a time to see what your problem/s might be.

Even for long time mechanics I suggest that the first time one works on this stuff that they have a ' mentor or guru' ON SITE... for safety reasons...
And I suspect you are not a long time mechanic... and we all start out that way.... so you really should find someone LIVE at your location to do this with you at the very least.