Just thought that some of you would be interested in the results of my "Stop
the Leak" campaign.

What I did was first put duct tape on all of the fresh air duct connections
under the dash (the round tube ducts that provide fresh air to the dash
vents and "heated" air to the tiny side defroster vents).  This kept cold
air from leaking out of those previously loose connections.  It seemed as if
my flaps internal to the heater assembly unit had properly functioning
seals, so that wasn't a problem for me.  If this is your problem, heater
disassembly and dash removal seem the painful option.  (Try all of my
suggestions first, as they are easy and can hopefully eliminate most
problems.)

Then I completely covered the air intake tube located behind the top front
grill, using appropriate amounts of duct tape.  The ambient temperture was
about 35 F, so the duct tape stuck properly.  At low temps, this is not
usually the case.

These techniques were so successful that I had NO COLD AIR leaking into the
van.  However, even with the fan running, the volume of heated air was
diminished substantially.  Additionally, I was getting fogging on my
windshield and side windows from the water vapor resulting from my
breathing.

To rectify both problems, I removed some duct tape from the air intake.
Specifically, I left the air intake plastic grill fully covered, but untaped
the triangular openings (which were designated as mouse holes in my earlier
post) which are located on each side of the main air intake grill.  (I will
keep the main grill covered until Spring, but this is probably overkill.)

This allowed air flow to return to normal.  When driving, air flowed into
the van, even without use of the fan.  It can be heated using the
temperature control lever, just like the elfs at Wolfsburg designed it.

My conclusion is that the most important aspect of stopping air leakage is
to be sure all internal portions of the ventilation system are secure and
leak-free.  If so, it seems that the originally engineered design is quite
adequate.

It should be noted that although this air leak issue became a problem
because of cold air infiltration, it works equally well in the summer to
stop hot, humid air infiltration which reduces the efficiency of our a/c
systems.

Budd Premack
86 Syncro, 84 GL, 73 Super
Minneapolis, MN (Land of Frozen Waters)