At 02:27 PM 7/11/2010 Sunday, mark drillock wrote:
>Yeah, you are right that the fan can push some fresh air out the end
>vents when the vehicle is stopped in early types. There are some gravity
>flaps that push open when under way and let fresh air get directly to
>the early hoses without passing through the fan.

Bingo -- if you can't hear those flaps snap shut when you suddenly
turn the fan on full speed, they are no doubt stuck open or
completely fallen off (both from poor design choices) and will negate
the effect of the blower.  The system will still work fine from ram air.

They are designed to fail, difficult of access and hard to fix, sorry
to say.  My fix on the '84 involved substituting metal end (pivot)
pins for the worn out plastic, no mean trick in itself; and driving
heated pins through the box itself to substitute for the silly little
molded clips.  The system wouldn't be so bad except that the flaps
hang from the open end of the clips -- the pins wear triangular and
then jam or fall through completely.  Difficult of access is the
polite way of describing the situation.

Yours,
David