Is the AC run by the very needy Nipondenso system? If so, only MBZ rebuilds can handle R134 reliably, or blow up withhin 2 months. I went through that already with my 190D with the 2.2L. Was convinced to convert to 134, and the pressure was so great it busted the bracket on my alternator, not once, but twice!!!!

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1983 300D, the "Avocado"
1976 240D, 4-spd the "Pumpkin", SOLD to Pierre
1984 190D, 2.2L, 5-spd, my intro to MBZ diesels, crashed into in 2002