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300E Year 87
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3 Posts
Discussion Starter #1
Hi there,
After I have replaced my 300E 87 model’s the side air vent, I noticed that the centre air vent and all
the vent bulbs stop working. I also washed (blow) the engine area too. I relay don’t know what actually have caused for this trouble! Any help would be appreciated. Many thanks
 

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1993 300e 2.8
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179 Posts
Did you use a pressure washer or forced air? Sounds like you knocked a vacuum line somewhere. What did you replace? Just the vent louver?
 

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300E Year 87
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3 Posts
Discussion Starter #3
Yes I used a pressure washer 😳. Just changed the air vents for both sides. I will now check the engine areas to see whether any vacuum line is knocked out! But thank you much appreciated.
 

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Buncha W124's
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2,214 Posts
The vent bulbs are controlled by the dimmer in the instrument cluster. If the cluster lights work and the dimmer works, and none of the vent wheel bulbs are on, most likely the bulbs are either bad or not snapped into place on the vent itself.

Search for more info on the center vent, if it's not just a vacuum tube disconnected in the engine compartment. Pretty common for multiple vacuum pods to have failed after 30+ years, and it's time consuming to pull the dash and repair them properly.
 

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300E Year 87
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3 Posts
Discussion Starter #5
The vent bulbs are controlled by the dimmer in the instrument cluster. If the cluster lights work and the dimmer works, and none of the vent wheel bulbs are on, most likely the bulbs are either bad or not snapped into place on the vent itself.

Search for more info on the center vent, if it's not just a vacuum tube disconnected in the engine compartment. Pretty common for multiple vacuum pods to have failed after 30+ years, and it's time consuming to pull the dash and repair them properly.
Thank you. Bulbs are working now! I don’t know how it that happen though!
I have looked around the engine to see any disconnected vacuum tube but couldn’t see! I am pretty sure this should be related to engine wash! Is there any diagram for such vacuum tubes in engine? Way to look for?
Thanks again much appreciated
 

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Buncha W124's
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2,214 Posts
There is normally a silver decal above one of the headlights with the vacuum diagram. Otherwise, there are vac diagrams in the factory manual.

To fully diagnose the climate control pods you need to pull the glovebox and test each of the 7 lines from the manifold with a MityVac, and also verifying vacuum is present at the top (inlet) of the manifold with the engine running.
 

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1996 E320 Cabriolet
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253 Posts
Dave, would a high cold idle on start up for three seconds to 2000 rpm be related to a vacuum leak?

Any tips on replacing the vacuum actuator diaphragms for the manual heater flap control mechanism... I know you had the auto system in the US, we had manual as standard here, and it is clearly not having the flaps do much when spinning the dial, they do operate a little bit but not as much as they should. Wondering if the two issues are connected...??
 

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Buncha W124's
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2,214 Posts
Idle issues in general could be due to a vacuum leak, but it would probably have to be larger than a single 1mm ID vacuum tube disconnected.

Unfortunately I am not familiar with the manual climate control system, I have never owned nor worked on one of those. However, based on the EPC diagrams, they share about most of the same vacuum pods.The automatic system adds a vac pod for the defrost and footwell flaps, which the manual system does not have. The other four (2 recirc/main air, 1 center vent, 1 diverter) are the same and require removing the dash to R&R.
 
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