Larry, this is on a 89 420SEL.
I decided to check the pressures again today as it was 95F outside. The results put the system on the low side. It was only reading 15-18 Low, ~160 High at high idle condition.
I added more R12 until I achieved about 20-22 Low, 230-250 High at high idle. This gave me about 48-50 F at the vents. So 45-47 degree temperature differential. It should be nice and ice cold when 75-85F ambient temps hit I'd wager.
In my googling I found a book that might be helpful:
Automotive Heating and Air Conditioning - Mark Schnubel - Google Books
Around page 185 it has a nice section on diagnosing various conditions on R12/R134 orifice tube and TXV type systems. Might be helpful to some of you out there.
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