My 84 300SD (W126) didnt shut off with the key yesterday for the firs time (320K mi) No problem use the shut off lever then read up on debugging the system.

Without a vacuum gage/mity vac I have determined I have vacuum at the brake booster (checked a line and it pulled some vacuum on my finger). jumped to the conclusion it was the keyswitch of vacuum shut of valve at the engine. Pulled the shut off supply line near the brake resivour (brown one) with engine running sucked on it and nothing, shut key off and sucked on it again and the engine shut off. So I started it up again and pulled the climate control supply line (red and?) and shut the engine off, then I blocked the opening for the supply and the engine shut off.

So it appears I have leaks in the ACC vacuum system. which leads me to two questions.
One if I plug the ACC suply line I can shut off the car with the key, the question is will the system default to defrost mode? I figure this is acceptable in the cold till I can get the time to take apart the dash to debug the ACC vacuum. I figure I'll have to get a mity vac at the local auto parts place now, a chance to buy a new tool

Two - anyone have a W126 ACC vacuum debug procedure? I havent found one searching yet.

As usual when one thing goes wrong somthing else goes wrong as well, this had to happen when the W124 is disassembled waiting for parts!

Thanks for any help
Paul