R129 (2000 SL320) Centre Air Vents stopped working

[Shottenden]

I don't know why but the centre air vents stopped blowing anything a few weeks ago. The aircon works fine and so does the heater. The side vents work fine. If I press the red button on the vents the top and side give warm air and if I press the blue button the top and side vents give cold air. The symbols on the screen just show forwards and footwell (not screen) but air is still coming out of the screen vents regardless. It is like some flap inside is not switching between screen and centre vents.
It is not a huge problem but wondered if there are some quick and easy checks I can do. I went through the diagnostics on the climate control panel but no fault codes were shown.

 

[grober]

IIRC the early R129's had electrically switched pneumatically operated flaps via vacuum diaphrams---eventually these perish and leak= fail to operate---- later models may have gone completely electric not sure. snag with electrically switched pneumatic valves is the electrics can be fine [ no fault codes] but fail to operate because of vacuum leaks.

R129 climate control vacuum schematic

www.benzworld.org

 

[Shottenden]

IIRC the early R129's had electrically switched pneumatically operated flaps via vacuum diaphrams---eventually these perish and leak= fail to operate---- later models may have gone completely electric not sure. snag with electrically switched pneumatic valves is the electrics can be fine [ no fault codes] but fail to operate because of vacuum leaks.

R129 climate control vacuum schematic

www.benzworld.org

Thank you. I’ve read about the vacuum system. Seems incredibly complex but these cars were very advanced for their time. I assume you mean passenger side UK?
I’ll look in the morning. Is it easy to have got kicked and something dislodged?

 

[grober]

Thank you. I’ve read about the vacuum system. Seems incredibly complex but these cars were very advanced for their time. I assume you mean passenger side UK?
I’ll look in the morning. Is it easy to have got kicked and something dislodged?

More likely to be a perished operator diaphram- you should be able to test its vacuum integrity by identifying the operating line and using a handheld vacuum pump. getting at the operator itself may be a different matter if its leaking!!

 

[grober]

this is for a C class but basically the same principles apply

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[Shottenden]

More likely to be a perished operator diaphram- you should be able to test its vacuum integrity by identifying the operating line and using a handheld vacuum pump. getting at the operator itself may be a different matter if its leaking!!

Thanks - beyond me - probably need to find a decent independent MB garage that knows about R129s in Kent.

 

[grober]

Thanks - beyond me - probably need to find a decent independent MB garage that knows about R129s in Kent.

As you can see main problem is access and a familiarity with this older technology- not all independants will be familiar -so ask specifically how many they have actually repaired? labour costs may be high

 

[Shottenden]

As you can see main problem is access and a familiarity with this older technology- not all independants will be familiar -so ask specifically how many they have actually repaired? labour costs may be high

I found the fault and fixed it myself for under £3 for a new vacuum pipe connector.

 

[grober]

Glad it was a cheap fix- somewhere accessible and not deep in the innards of the heater/aircon assembly! was the leak on the air handler assembly itself or the 15 way switchover valve assembly?

 

[Shottenden]

Glad it was a cheap fix- somewhere accessible and not deep in the innards of the heater/aircon assembly! was the leak on the air handler assembly itself or the 15 way switchover valve assembly?

Just lifted bonnet and it was on UK near side near bonnet hinge. A small connector block. Easily visible and accessible. I was very chuffed and lucky I think.

 

[Shottenden]

Just lifted bonnet and it was on UK near side near bonnet hinge. A small connector block. Easily visible and accessible. I was very chuffed and lucky I think.

 

[grober]

A picture is worth a thousand words---may well help a fellow R129 OWNER in the future.

 

[RichWeath]

I found the fault and fixed it myself for under £3 for a new vacuum pipe connector.

Where is this located please as I have simiIlar issue, excepts it's drivers side vent.

Thanks