If you are simply replacing the oil with the correct amount, just dump whatever is in the compressor and let it drain a bit, and fill into the suction side with the correct amount (which I do not remember at the moment). Use PAG oil.

It is not necessary to flush the rest of the oil out unless you need to remove debris.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!