85 W123 300D.

When running air conditioning the car shifts a bit harder, and engine runs for a 4-5 seconds after turning off key.

No A.C, no issues.

Where should I look for a vacuum leak?

Thanks

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Current : 1988 R107 560SL

Previous: W123's, W211, w210 E55, W463's, W108's, W111

Check the vacuum-operated valves and flaps in the climate control system, buried in the dash (unfortunately). Pull the ash tray and the radio; in front of them is a set of vacuum valves. You can remove each vacuum line and test it with a Mityvac. Any line that won't hold vacuum is probably connected to a bad flap actuator. You probably have a flap actuator with a failed diaphragm. Some are fairly easy to access, some difficult, and some impossible, without pulling the dash. There's a lot of info on this forum on the subject. Use the search function.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

I will read more into it

Not sure how confident I am about digging into the dash. Oh well!

__________________
Current : 1988 R107 560SL

Previous: W123's, W211, w210 E55, W463's, W108's, W111

Probably the vacuum pod that opens the center vent flap is leaking. Do you get air out the two center vents when cooling the car? Testing them is pretty easy. I don't recall having to pull the radio in a 123, just the trim and the climate control pushbuttons - but it has been years since I last owned a 123.

The hard shifting is partially because you are giving the car more throttle to overcome the additional load of turning the a/c compressor. Though it does sound like you have a decent sized vacuum leak, given the run-on condition.

I am in fact getting cold air out of the center vents.

About 2 months ago, I did have them Tee off a door lock, as I had a vacuum leak that was effecting shifting.

__________________
Current : 1988 R107 560SL

Previous: W123's, W211, w210 E55, W463's, W108's, W111

So my A/C is working fine, switches vents, stays cold.

Should I look behind the pod? And how?

__________________
Current : 1988 R107 560SL

Previous: W123's, W211, w210 E55, W463's, W108's, W111

Rather than tear it all apart to get to the pods that are buried, just access the five control solenoids that are located behind the climate control unit in the console, above the radio. You may also need to remove the switch panel above the climate control. Each solenoid has a common line from the vacuum source and a line to one of the pods.

With the solenoid valves exposed, start the engine and run the a/c. Confirm that the engine shutoff is still delayed as you described in your first post. Now disconnect each solenoid in turn until you find one that restores the engine shut-off time to normal. The leak is in that line. (It's possible there is more than one leak, which will take more work, but you see what to do.)

To disconnect each solenoid you can either pinch or remove each vacuum line. If you remove a line, be sure to close off the vacuum source line so you aren't creating a leak even worse than the one you are trying to fix.

Once you have found the one that's leaking, figure out which pod has the leak. If you don't have a manual, re-post with information on which one leaks (number the solenoids #1--#5 from left to right) and we can tell you. Knowing which pod leaks will also tell you how much work it is to access that pod.

Depending on the difficulty to replace that pod, you may choose to seal off the vacuum line and ignore the problem for now. I did that with my '85 300D-T and eventually fixed it when I replaced my badly cracked dash.

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

It might be easier to select the OFF mode for the climate control before turning the key off. (If a slightly delayed shut-down is the only issue.)