Ok, I understand what the free-swinging flaps do in the heater box.  They
matter...

Heater box has three functional parts: cold air inlet, cold air plenum, hot
air plenum, arranged top to bottom.  The blower is the obvious connection
between the inlet and cold plenum, but VW added two big holes (about 3x6"
each) so that ram air wouldn't have to pass through the blower to get into
the plenum.  But now of course the blower output is short-circuited right
back to the input; so they added a couple of very light swinging flaps that
close off the holes whenever the pressure is higher in the plenum than in
the inlet.  The design (if you can call it that) of the flaps is such that
they ordinarily fail open, either by sticking or by falling off.  Either
way, result is that you get greatly reduced blower output.

The flap design is bad because they made the wearing parts out of plastic,
and doubly so because the pins on the flaps hang from the open ends of the
little clips they're stuck into instead of from a solid part.  So as the
pin gets smaller, the opening also gets wider until the flap falls off.

Fixes -- 1) new middle section (that's where the hinges are) and new flaps;
2) build up the pin thickness with epoxy -- it's unlikely to have broken
off completely -- and make new hinges.  This is hard because there is no
access.  I succeeded by heating brads and driving them through to support
the pins, but it's still hard; and you have to remember to put the flap in
before the second hinge since it no longer snaps into place; 3) in a pinch,
close off the holes permanently.  This will reduce the flow of ram air
because it will have to pass through the blower, but it's better than nothing.

These flaps are covered with light foam (easier than putting a narrow strip
on the edges) but I see no need to renew this as it mostly reduces the
noise of the flap hitting the frame.  As long as there aren't lumps
standing up in some places and not others, there should be no functional
difference.

david
ps -- we might consider a contest for how far someone can send one of the
spring clips that hold the box together -- and still recover it.  They're
snappy little guys, pays to hold your finger over them whilst
removing.  Did I hear they're close to $4 each at the dealer?

pps -- I would strongly recommend replacing the M6 screws holding the
heater box to the vehicle with M6 bolts instead, and generously anti-seized
at at that.  This is an area that takes a hit when the windshield leaks,
and the ends of the upper four screws/bolts are out in the open
anyway.  Might similarly replace the Phillips screws on top of the dash
with hex-head screws as they are quite difficult to drill out with the
windshield in place.
David Beierl - dbeierl@attglobal.net <<- New address becomes mandatory on 1
Oct, optional until then.