So I am having a problem with my 300TE's A/C...
I think there is a blockage in the system somewhere, but I need help diagnosing this first.

I evacuate the system, and vacuum down to ~29 hg. The problem is that with only 12oz of refrigerant, I am getting 45/320 psi lo/hi. (25/380 at 1500rpm).
That is only a 1/3rd of the recommended capacity for r134a (the recommended is ~28oz). Why would my pressures be so high after only ONE can? The only thing I can think of is that there is a blockage?

Could there be anything else that could be causing this? I'm purging the lines of air before I begin and vacuum held fine for 30mins after I shut off the valves.
I need some help diagnosing here its driving me crazy!!!
Is there a specific test I can perform so I don't have to waste hours and hours swapping parts unnecessarily?

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
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2003 Gray Mercedes ML350 - 122k