Is a/c and central locking system on the same vacuum system? The reason I asked is that they both stopped working. I took the car to the dealer a couple of years ago and had the a/c converted to R134. The car cooled wonderfully that summer and last summer. When I tried to use the a/c the other day, it didn't respond when I turned the a/c button to the on position and switched it to max a/c on the control panel. Also the central locking system is malfunctioning. When I lock the driver's side door, the other locks do not lock i.e, the trunk,the fuel tank,and passenger door. The car is a 79 300cd. Please help because I really need my a/c soon.

The source for all vacuum used is the vacuum pump. It covers vacuum storage, locks, transmission shifting, engine shutdown, power brakes and the air cond controls.

Did you notice a change in how the trans shifted? Maybe a clunk when you come to a stop or a bit harsher shift?

It goes from the pump to the brake booster via a hard line. First thing you need to do is see if there is vacuum in this line while it is running and then see what happens to the level when you turn it off. There is a tee in it to plug a vacuum gage in.

After that point, you need to check the vacuum on each main circuit to see which might have a leak and then go through that circuit finding where the leak is.

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1980 300TD-T (82 Turbo and Trans) 159,000 Miles "Jackie-O"
1983 300SD 272,000 Miles "Aristotle"
1987 Jeep Wagoneer Limited - keeps the MB's off the ice and out of the snow
1994 BMW 530it

Check the vacuum lines near the oil filter. It is common for them to be knocked loose at oil change time.

Good luck,

Thanks,
I went outside a few minutes ago, and low and behold I found that I had a vacuum hose off in the area of the oil filter. The hose was green w/yellow stripe. I had the oil changed last week and I guess they knocked this vacuum line off. Larry you hit it right on the head. Thanks for saving me a trip to the dealer. It's no telling what they would have charged me to "put the vacuum hose back on" I really appreciate your expertise Larry. You saved me a day off work and possibly $$$$. I promise to check with you guys on this website for now on before I even think about going anywhere else. Thanks a million.

Glad to help. Even a dumb old man like me learns a few things along the way.

Have a great day,