When flushing an a/c system do you flush only the condenser or both the condenser and the evaporator.

Also, I want to use the compressor from my totalled '86 300E in which the A?C was working perfectly in an '86 300E that I just acquired. The old car had R134A but the new one is an R12 system.

How do I flush the compressor to use it with R-12?

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1986 300E (3/2002) Rear ended and totaled (10/2009)
2000 Xterra (5/2000)
1992 400E (11/2009) -Sold
1986 300E (12/2009) - Sold
2004 E500 Wagon (6/2013) - Sold