R129 1999 No air from centre airvents

[DrNick]

I've just recently noticed that I don't get much (any) air from the centre vents on my R129 99 500SL
Selecting the manual air directing button (the one with three triangles on the LCD) only allows me to select "Down" or "up" or "Down and Up". It never allows the "out" arrow to be selected.
Any ideas what might be happening?

 

[Doodle]

The centre vents are controlled by the red and blue buttons in the middle of them.

 

[DrNick]

Thank you for that - the red and blue buttons were hidden behind a clip on phone holder. Having reverted to the manual again these are mentioned grudgingly!
However, this seems to only relate to the temperature of the air, not the amount (again according to the manual) and I'm getting no air even if I twiddle the knob for amount. I'll go and try the buttons later but the book is a bit economic when it comes to explaining the purpose of this system. eg does the blue button always give maximum cold air and the red button give maximum hot air. Surely no buttons means just normal temperature air? The book is quiet on this. And why have a symbol on the LCD that is non-functional. Again the book doesn't go into detail.
I'll go and have a play later

 

[Doodle]

It is a bit arcane. From memory on my 1995 example, you can have it working either when all face vents are set active, or independently by using the buttons. The fan speed is governed by the climate panel, you can then moderate the centre using the middle wheel. I wouldn't say maximum on the buttons, but appreciably warmer or colder.

Of course, it assumes that something isn't broken, which it sounds like might be the case if your out/face vent mode isn't available on the climate panel.

 

[Wearsthefoxhat]

Possible fault on the air manifold, often cured with some araldite. They seem to crack slightly.

 

[DrNick]

An update. I had a play yesterday and it all burst into life. It turns out that the little blue and red buttons on the air vents control the outward pointing arrow on the LCD display in the climate control and this control the airflow from the vents. The AC control unit has no direct control over the centre vents. I'm pretty sure the manual is unclear on this point. in my defence!
(On reflection this is exactly how Doodle described it, so thank you for that)

 

[Doodle]

Agreed, the manuals are pretty useless at explaining it's operation.