Try:
www.griffiths.com
to learn all you ever wanted to know about Porsche and other a/c systems. It was this site that educated me as to how much work and money I would need to rebuild my cars OEM a/c. (All parts of which are now sleeping in a big cardboard box in the basement).
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Doug
'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
members.home.net/zielke/911SC.htm