>
> Early Vanagons used the same system as Buses -- there is a vent on the
> inside of each front door at the lower rear corner.  These vents can be
> manually opened or closed by sliding a blue knob fore or aft.  These
> vents vent interior pressure to the insides of the doors and from there
> presumably to the outside.
>
> Later Vanagon eliminated these door vents and went with the always-open
> vents behind the rear side windows.  They serve the same purpose, hence
> the puff of air from the vents as mentioned above.
>
As an aside to this, I've noticed that the Westy pop-top serves as a
pressure-equalizing device on my '81.  When I shut the door I can see
the pop-top front edge lift a tiny bit as air under pressure is forced
out.  It pops up a little more when shutting the rear hatch or the
sliding door.

--
Sean Bartnik
Fredericksburg, Virginia
1981 Volkswagen Vanagon L Westfalia
1974 Volkswagen Karmann Ghia convertible
http://www.type2.com/bartnik/myvan.htm