So Mark McCulley says:
> As far as I can tell, there is no way to block outside air from entering my
> '87 Vanagon. Most vehicles have recirculate/fresh control which
> accomplishes this. I _think_ I understand the heater controls, but maybe
> not. I just want to be able to block diesel fumes from entering the cabin
> when I'm sitting behind a bus (as in Greyhound). Should I pack gas masks?
> 

I had this same problem on my '91.  I don't know if the configuration for
them are the same or not.  In mine, it is the defroster control that controls
outside air from flowing in or not.  After making the mistake of letting the
dealer try to correct this problem only to tell me that that was the
way it was suppose to be, I looked at the setup myself.  With some tips
from Joel about how to access and look at the cable for the defroster
vent I was able to follow the control wire that connects to the defroster
lever to it other end where it connects to an lever on the air distribution
box.  This lever was loose on mine and this turned out to be because the
pin on the cylindrical edge of the lever was bent in so that it couldn't
hold the lever in its slot securely.  So I high tech solution of cutting
a small piece of cardboard and shoving it between the pin and the main
body of the lever and pushed it back in it's slot.  Works great.  Ocassionally
I have to replace the cardboard as it slowly gets squashed.  To gain
access to the distribution box lever, you need to remove the glove box.
It just lifts out.

Hope this helps!

Steven 

sjohnson@pcocd2.intel.com