I'd tell ya if I did - but I am not too knowledgable in that area. Do you have the Factory Service Manual(s) for your z31? They are extremely informative and indepth and do cover air conditioning/heating items where the Haynes manual does not.
If you do not have a copy and would like an electronic version I could post a link for you to download a copy tomorrow morning. Let me know here on the post or via email and I can do that. The "ha.pdf" that covers heating and air conditioning is very informative and includes diagrams.
This will take you to an area with each of the individual PDF documents. There is also a file in this folder that ends is ".rar". This file has all of the PDF documents inside of it, but you will need the program "WinRAR" to pull them out.
Let me know if you have any questions. Glad I can help out!