I bought a used R4 AC compressor at PullaPart yesterday - it looks good, no visible signs of oil leaking, clutch turned by hand, and when I disconnected the hoses, the system was still pressurized.

What else should I do to test it before installation? Can I pressure test it off the car like this?

I have 30 days to take it back...

Ryan

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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

Install, and check pressures. Its a pump. Unless your pumping you really can't tell. It does have valves and seals that do wear out and need replacing.
Good luck.

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92 300D 2.5L OM602 OBK #59