Many times oil will be left in the compressor. Mercedes has a spec in the TDM that is 40cc of oil for "sudden emptying of system". This is the rule of thumb. Now, when replacing parts, you have to add oil for each part. Each part has a different amount.
By the book, you are supposed to remove the old compressor and drain the amount of oil out of it when replacing and measure it, just to know. Then Mercedes has a process of figuring out how much to put back in. I just go by how much the factory fill is because I have seen so many dry.
1991 GMC Syclone
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