Gents,
I found this thread after starting my own:
Vacuum questions on '87 300SDL
The information here was very beneficial, Icesailor, but what about my hissing sound? Any ideas on isolating it or just replace all the vacuum hoses under the dash? It hisses off and on when on the A/C or EC settings. Have not tried the max A/C setting yet.
My limited skill at this tells me it is a vacuum leak. On the other post Jim suggested checking the hoses as they go through the firewall.
Thanks for any and all help.