I read a previous posting where the person had the same problem as I am having. The middle two vents on my 87 300 SDL is not blowing any air. The air seems to come from the other two vents, the rear vent, and the defrost vents. I am pretty sure their is a problem with the inline screen for the vacuum pump. I was wondering if someone could guide me in the right direction by telling me where it is located.

At the front of the engine just inboard of the power steering pulley is the vacuum pump. It has two connections - a big pipe to the brake booster and a smaller vacuum hose. 3-4" up from the connection is a small plastic filter. I think it's yellow. That's where the bad screen is.

If that's not the problem, you probably have a bad diaphragm in the center vent acutator.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

Any one have any suggestions/techniques on the best way to remove the dash so I can check if diaphragm in the center vent actuator has gone bad. I would appreciate any help given.

The best way to remove the dash is to have someone do it

You don't have to remove the dash to get to the center vent actuator. Try this:

- open the ashtray
- remove the ash receptacle
- remove the two screws at the bottom of the ashtray frame (don't let them fall under the console)
- pull out the ashtray frame
- reach behind and pull out the radio
- remove the two screws holding the ACC control panel in place
- pull out the ACC control panel
- remove the various electrical connectors and fiber optic lines from the switches. It's pretty hard to get the connections wrong but make labels if it'll make you feel better. No need to label the fiber optic lines, they're all the same.
- look for the center vent actuator in the upper right corner of the cavity. It's casing it pink with a vacuum nipple pointing out at you.

Apply a vacuum to see if it works. If not, scratch your head to figure out how to replace the actuator. I can't figure out how to remove it with or without the dash in place because the far end of the actuator is deep in the vent. The manual says to go in through the venetian blind, but it doesn't lead to the same place. BUT you can get a replacement diaphragm and fix the actuator in situ. Takes some delicate fingers but I was able to do it.

There's a battery of tests you can do before tearing into the console. Start by checking if the system will hold a vacuum downstream of the yellow check valve ahead of the brake booster. You can also check each actuator from the vacuum junction block inside the right console panel. You have to drop the passenger side lower dash panel before you remove the right console panel. Check that each line holds a vacuum and that you can hear a flap actuate. It'll be an obvious and familiar sound if you've been in a 126 with working ACC.

If one actuator is shot you can bet that others are shot as well.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

Sixto

Thanks for all your help. I got around to opening everything up this weekend. You weren't kidding when you said to scratch my head and figure a way out to get the diapraghm off. I'm going to try to remove the carpet under the glove box and see if that helps any. In the mean time I found out this weekend that my climate control switch has gone bad. I am going to order the part today and replace it. I'll let you know how things are coming along. Thanks again.

Just wanted to follow up on this post that I had put up a while back. I finally replaced the small plastic filter/strainer that is connected to the tube that comes from the vacuum pump. After replacing it I have noticed a big difference in the shifting of the transmission, it is a lot smoother now. Also the air that was blowing from the defrost vents has stopped and works as it should, only when turning on the defrost. However the center vents still don't seem to be working. My feeling is that the flap maybe stuck. If anyone has any suggestions or recommendations I would greatly appreciate it.

Time to break out the MightyVac and test each line at the ACC vacuum switching log. Remove the passenger kick panel, lower dash and right side panel of the center console to get to the ACC switching log.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

Not to be thick here but I'm only just getting into the DIY thing. I would like to check my screen also. Can someone help me understand exactly where this is on an 87 420SEL. Is the part available on FastLane? Do I need to somehow recreate the vacuum or can I just change this screen, hook it all back up and voila?

Thanks,

John

Sorry about the tread dyslexia. Someone else is having similar problems with a 300SDL. I don't know if a 420SEL has a filter or where it might be.

Sixto
95 S320
91 300SE
87 300SDL
83 300SD

I noticed today that their is a little bit of air blowing from the vents when the blower is off. Any reason why it would do that?

Probably because the recirculation actuators are shot. The default position of the actuators is everything closed except for the defrost vents and outside air intake flap. With the engine running and the ACC set to '0,' the outside air intake flap should close (recirc) giving you no air to any vent since the blower isn't running when the ACC is set to '0.'

The recirc actuators are easy to get to. Just remove the glove box liner and there they are. Then defrost vent actuator is to the left of and slightly higher than the glove box cavity.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

I am not sure but I think 420sel, being a Gas engine, does not have a screen, neither vacuum pump as a source. The vaccum source is the intake manifold, I believe. It has a vacuum pump under the rear seat but it is for the door locks. The vacuum pump and screen in the engine bay is for the Diesels only.
What kind of problem you are having John.

Thanks

__________________
87 420 SEL
Looking for a nice mid 80's MB diesel.
87 BMW 528e (Sold)
99 TOYOTA 4Runner
1989 Honda Accord (Sold)
1988 Honda Accord (Total)

Thanks, but just looking for another potential preventative to do. Have already fixed a bunch of little stuff -- learned on this board. Monovalve replacement yesterday gave me heat back but I'm still getting AC out of the defroster vents. With the monovalve fixed, and no vacuum filter, this seems to narrow it down to the diaphragm.

Thanks,

John