Okay, finally got to doing some diagnosing the ACC system on the 84 300D with the Mityvac. I have two problems. First the vacuum tubing that runs across the front of the engine to the EGR controls on the passenger side fender had contacted the water pump pulley and that caused a major vacuum leak. I fixed that and disconnected the green vacuum line at the firewall and plugged up the line. Test drove the car and it shifted wonderfully, silky smooth just like always. I connected the Mityvac to the green vacuum line and got these results:
ACC unit off = vacuum good, no leak
ACC unit on any other setting, cold or hot = didn't hold vacuum, leaked down fast. It leaked down extremely fast in the defrost setting.
I was able to keep pumping the Mityvac to keep up with the leak in other settings and when I did this I got heat to the floor vents. Once the vacuum bled off the floor vents closed. So whats this all mean? I am going to take what I can apart and start testing the individual vacuum elements with the Mityvac to see if I can figure out what is leaking. Any input appreciated. RT

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When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

Sounds like leaking diaphragms/tubing. Start with the ones you can reach. You can get to the ones for the floor by removing the drivers kick panel and looking toward the top of the driveshaft tunnel/toward the front. The other one you can see with this panel removed is for defroast if I remember correctly. I hate as much as the next guy/gal that these cars did not come with manual controls.

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Jim

sent you a PM, you've got mail.

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1980 500SE/AMG Euro
1981 500SEL Euro
1982 380SEL
1983 300TD
1983 500SEC/AMG Euro
1984 500SEC
1984 300TD Euro
1986 190E 2.3-16
1986 190E 2.3
1987 300D
1997 C36 AMG
2003 C320T 4matic

past: 1969 280SE 4.5 | 1978 240D | 1978 300D | 1981 300SD | 1981 300SD | 1982 300CD | 1983 300CD | 1983 300SD | 1983 380SEC | 1984 300D | 1984 300D | 1984 300TD | 1984 500SEL | 1984 300SD | 1985 300D | 1986 300E | 1986 560SEL | 1986 560SEL/Carat | 1987 560SEC | 1991 300D 2.5 | 2006 R350