We sorted this all out on this list a few years ago. The later
heater/airbox has 2 sets of possible hose connection points for the
large dash end vents. During the 87 model production they all started
coming connected to the set that provides only air that has first passed
through the heater core. Before that these vents had a more direct
source of outside air with better flow. The early setup did not allow
for heat to come out of these dash vents.

I have vans with both types. I prefer the better fresh air of the early
type Someday I may change my later model over to use the other port. The
hoses that connect to the 2 sets of connections are different sizes and
shape so you can't simply just move them to the other ports. You need to
get the hoses for the type you prefer.

Mark

Loren Busch wrote:

>RE: Fresh air vents
>Depends on the year.  '88 (IIRC) on the fresh air vent goes through
>the heater core, prior years fresh air was just that, fresh air
>without heat, good in summer, bad in winter if the seals had
>deteriorated.  My '85 was great, plenty of fresh air when needed
>through the vents.  My '90 provides little air w/o the fan on but it
>is nice to get warm air from that source in the winter.  I'd rather
>have the pre-88 setup most of the time.  I've never explored the
>possibility of rerouting the air in the '90 but I understand the air
>plenum is different on later models.
>
>
>