Hi -
My '80 has a similar problem. I have to re-adjust the ends of the 
control cables at the change of hot-cold seasons.  The travel allowed 
by the control arm in the dash is not enough to accomodate the 
necesary travel to go from fully opened to fully closed.  It's a 
nuisance, but I absolutely refuse to have a VW without a heater (just 
on principle!)
Make sure the dash control is set for no hot air, adjust cable ends 
until vent is closed off.  One side of mine is a nut, and the other 
is s screwdriver clamp.  They can be accessed and seen thorugh the 
tire opening.
- Jeff '80 Westi

> My mother has a recently purchased '87 Vanagon Wolfsburg Ed. There is a
> noticable and uncomfortable draft of warm air comming from under the dash.
> I haven't seen the van, but she claims to be turning off all of the heater
> controls. This is more and more annoying as temperatures rise in mid
> summer.