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Old 09-13-2000, 06:19 PM
fz500sel's Avatar
Happy now in paradise!
Join Date: Nov 1999
Location: Venice, FL - "sharktooth capital of the world"
Posts: 712
No center vent air on my '85 300D. I took out the glove box and sides from the center console so that I can observe the actuators. When the fan is on (EC or AC) The actuator behind the glove box turns fully. There are 2 other actuators behind the center console. One has the usual vacuum line going to it, but the other one has 2 lines. One that connects to the end and the other hose connects to the side of the actuator. The one with only 1 hose will actuate and turn the flaps so that air is diverted to feet BUT ONLY WHEN PUSHBUTTON FOR BOTH TOP AND BOTTOM is pushed. If I push the button for bottom vent only, it will close the vent and air will ONLY BE COMING OUT OF THE SIDE VENTS. I hooked up my vacuum gauge to the actuator that has 2 lines to it and I don't get any vacuum on either line. I hooked up a good vacuum source to it while the A/C was running and it DID actuate but I still only had air coming out of my side vents. When I look into the center vents I can see some flaps but even when I actuate the actuator by hand those flaps don't move. I'm wondering if maybe I have a some linkage to those flaps broken. I would have to pull the dash to investigate further.

My questions are: 1) why does the 1 actuator work opposite to the way I would expect? It should divert it to your feet when you have the bottom only pushbutton pressed.

2) are those vents that I see thru the center vent console actually tied to the linkage of the 2 hose actuator? My thoughts were that maybe it is turning a vent behind the console that I can't see and the vents I do see will open by air pressure when air is forced thru them.

Sorry for the long post. Just trying to understand this a little better.

84 500SEL EURO 87K
85 300D 267K (and still goin' strong)
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Old 09-13-2000, 08:23 PM
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Join Date: Jul 2000
Posts: 72
Had the same exact problem with my sister's 1984 300CD. Don't take the dash apart. The problem is with one of the vaccum solenoids that opens the center vent.
Remove the a/c push button unit, be careful not to break the wood when you pull it. It is held in place by plastic pins.
Behind the wood you will see some phllips screws, they hold the push button unit in place.
Behing the push button you will see four vaccum solenoids.
1) Defrost
2) Feet
3) Center Vent
4) Bi-level
Not sure if that is the sequence but I am sure it is close. If I remember correctly the one that controls the center vent is no.3 from left to right, to find out for sure:
Turn temp wheel to min.
Turn on car and a/c
Put your hand on the solenoids and try the various functions on the push button. The one that doesn't click should be the one for the center vent. I think they are $29.00 at the dealer.
The button with the arrow down is not to direct air to your feet. This system does not allow that selection separately. Arrow down is normal a/c, arrow up and down is bi-level - hot air only, the others are self explanatory. The arrow down function will direct air to your feet after the system detects it is too cold or when you have a temp selected that requires heat, it will then close the center vent and blow on the sides and feet only. That is the way it is supposed to work anyway. These systems almost never work perfectly.
Good luck
Joe Brasileiro

[This message has been edited by jbrasile (edited 09-13-2000).]
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Old 09-13-2000, 11:42 PM
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Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
I would check all of the vacuum actuators for leaks. One leak can cause a weird system operation problem. You can check all of them at the vacuum valve block.

You may need a manual to do this because you will have to identify all of the colors of the lines.

We sell the CD for this chasis and it has the vacuum diagrams in it.

Donnie Drummonds
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Old 09-14-2000, 01:42 PM
fz500sel's Avatar
Happy now in paradise!
Join Date: Nov 1999
Location: Venice, FL - "sharktooth capital of the world"
Posts: 712
Thanks fellas.

Where is the valve block located at Benzmac? According to the Cd it looks as thought the suspected faulty actuator is behind the climate control. I will need to pull the dash to get to it though. Seems like a lengthy process (pull instrument cluster,etc.). Started on it yesterday, wanted to finish today but it is raining. Unfortunately, my better half has the garage filled with her "crap" and I don't have room to work on it in there. Guess I will have to wait for another day.

By the way, how was your vacation, Benzmac?

84 500SEL EURO 87K
85 300D 267K (and still goin' strong)
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