1997 C280, well maintained, 110K mi.

The center dash vent no longer flows air -- air only flows from the defrost and side vents. Also, possibly related, the rear headrests wouldn't retract when the button was pressed.

Research shows both symptoms can be a vacuum problem. I've read that the air vent problem *might* be caused by a faulty "vacuum pod." But how to I access it? I cannot find any how-to data.

Inspecting under the hood, I found a gray vacuum line that was off. It was near the oil filter, under the intake manifold (thanks no doubt to some knuckle-dragger at Jiffy Lube).

Time for a test: I started the engine, and hit the button again. Down the headrests went! Next, the air-con controls: I cycled through the air-direct button and, for the first time in many months, I was greeted by a blast of cold air from the center vent!

However, after a few minutes, and more cycling tests, the air stopped coming out of the center vent. As far as I could tell, everything else still worked (including the head rests). Aw, @#%$!

I tried driving it around the block, going from light- to full-throttle, with speeds up to 60 MPH. Still no center air.

I guess it's a combination of problems. Do these clues ring a bell with anyone? Still sound like a bad vacuum pod inside the dashboard?

Any help would save me hours and hours of troubleshooting.

Thanks in advance.