When running my a/c; about half the cold air flow comes out the defroster and half comes out all 4 dash vents. When turning on just the defroster, it blows hot air out the defroster vents with good force as expected. I have read a lot of threads on the subject and it looks like a vacuum actuator could be bad. My question is: which actuator is the likely culprit? Center vent or defroster actuator? Some posts indicate the center vent actuator but there is reduced air flow out all 4 vents. I'm leaning toward the defrost unit being bad since minimal, if any, cold air should be coming from there. Any advice is appreciated.
Thanks
John

__________________
1985 300TDT
2013 E350 Bluetec

Sounds logical to me. The defrost actator is "relaxed" during defrost but vacuum is applied while in cooling compressor mode.

Here are some diagrams to help:
http://www.startekinfo.com/StarTek/outside/12265/disc_2/program/Climate/83-604.pdf

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

Thank you for the diagrams. They are a big help understanding what vents should be open or closed depending on a/c setting. If I'm reading it right, when its hot out and the center button is pushed for a/c; then the majority of air flow should come out of the dash vents and very minimal flow out the defroster... so this leads me to believe my defroster actuator is bad and not the center vent actuator; anyone else agree or not?
I'm hoping its the defroster one because its easier to replace

__________________
1985 300TDT
2013 E350 Bluetec

Thanks for that great diagram!

I don't get any air out of my center vents, I had guessed because of some issue with the vacuum flap behind it. Is there a way to manually pump that line or jam the vent flap open so that air will flow out of the center vents?

In the diagram, there's a straight line running from the regulating switch (4) to the center jets vacuum element (40) - if I could get at it without removing the dash, that would at least give me something to tinker with.

Yes, the best way to determine if a vacuum element is leaking is with a mightyvac. Access to the manifold of switchover valves is behind the kick panel, on the passenger side of the console.

I believe the system is set up for:
NORM = center & lower dash side vents
T/V = center, lower and slight amount of defrost

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )