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Heat/AC/Fresh Air Flap
>>Can anyone out there tell me how the "freah air flap" on my '83 UrQ is
supposed to work? The thing is very solidly shut; it resists even "firm"
pressure applied by hand to open it, so something is actively holding it
shut (as opposed to whatever pulls it open being merely disconnected).<<
Where is it and I can go look at mine.
Dave Lawson email@example.com
Pulling that flimsy plastic guard back reveals a big mutha vacuum servo
connected to the fresh air flap. Breaking the vacuum circuit (!whoosh!)
causes the servo to "relax" and the air flap opens, so in fact the servo
seems to "work" just fine (amazing how strong a bit of vacuum can be!),
as does the flap.
The vacuum line of course disappears through the firewall (actually, I
guess this is past the "firewall", yet before the dash/windshield -- I
wonder if this would qualify as a "plenum" ??). From the inside, I can
see a vacuum line that runs along the lower right (passenger) side of
the heater/duct unit (with AC coils to the right and drip tray to the
right), but can't see where it terminates. The other end of this vacuum
line disappears upwards into the nether regions of the dash above the
WFT (Whole F*****g Thing), and is -- I suspect -- the side that connects
to the fresh air servo flap, although whether directly or through another
dozen joins/relays/thingamabobs is impossible to discern.
The frigging Bentley manual is typically useless. It acknowledges that
AC does exist, and dedicates pages to different compressors, but nowhere
does it actually describe the control "circuit" (mechanical/elec/vacuum),
other than to say how to adjust the cables.
There is a small "thingie" mounted on the upper left rear of the control
assembly (three-levers for footwell air, windshield air, and AC/off/Heat)
with two wires and what looks like a thermostat connection that runs off
to the AC coil assembly). Anyone know what the devil this thing is? the
Bently manual doesn't even show an ink stain where this thing is, so I
am kinda mystified. Maybe the AC/Clutch thermostat/switch? (This is not
to be confused with the "AC microswitch" mounted on the lower left side
of the control assembly.)
If your talking about the fresh air inlet valve under the thin plastic cover
at the base of the windscreen..... normally it's open to let fresh air
into the interior, it closes when the A/C is on to prevent humid outside
are from getting inside. Working from memory here, I think it's vacuum
controlled by a electrically operated valve mounted on the ducting there
under the hood. Might be the same as the 4000/4000 Quattros?
So "normal" operation is open for heat and closed for AC? I wonder if the
AC will work with it open (I *know* that heat works with it closed). I am
beginning to suspect the easy solution will be to install my own "outboard"
electric vacuum valve (which is actually kinda neat 'cuz then I can tell
it to do what *I* want it to do, not what some damn furriner thinks is
teutonically correct...[note to the humor-impaired: I am being semi-sar-
castic/humorous here, no need to flame me for daring to question the
competence of the World's Most Perfectly Engineered Car and/or the World's
Most Perfectly Engineered Car's Engineers]).
I am also thinking of adding a switch parallel to the "A/C Microswitch"
to allow me to run the AC when on the heat setting -- which all (that I
have seen) Japanese cars provide. This allows defogging/dehumidfying
on those cold dank days (or when your heater sucks in great gobs of light
airy snow flakes and dumps the melted remains on your windshield...).
Anyone done this before? Pros/Cons/etc?