Re: Little Audi Problems

["Dick Green" <dick.green@valley.net>]

I wouldn't assume an electrical problem. A vacuum problem could cause the
same symptoms.
The recirculate flap is vacuum actuated and I would assume that the air
flaps are too. While it's possible that the whole climate control computer
is fried, you should check the vacuum system first. It'll probably be easier
and cheaper to deal with that. On my '93 90 Quattro (which must be very
close indeed to your '93 90CS), you can perform a quick and easy test to
determine whether the problem is electrical or vacuum. But first, make sure
that all of your fuses are OK (I doubt that has anything to do with it, but
it's so easy to do.)

The vacuum switch for the recirculate flap is behind the glove box. You can
get to it via the rectangular opening directly underneath the glove box (all
the way at the back of the passenger leg area.) This opening is the source
for the passenger compartment air feed in recirculate mode, and leads
directly to the recirculate flap. If you get down on your back to look
through the hole (shine a flashlight up there) you will see the vacuum
switch on the extreme right. It's a brass frame with a black cylindrical
switch housing inside, white plastic ports (nipples if you will) and one
brass port on the other side. Two black cloth-insulated hoses are attached
to the white plastic ports. One leads to a large black cylinder directly
behind the switch (that's the vacuum cylinder with the actuator arm for the
recirculation flap.) and one leads off towards the firewall. Obviously, the
one leading to the firewall is the vacuum source and the one leading to the
vacuum cylinder is the output.

If you can't see all of this clearly, you can remove the black plastic panel
(the one with the hole you are looking through) just by removing a few
bolts.

Start the engine, wait about ten seconds until the vacuum system comes on,
and remove the input hose. You should feel a vacuum. If there's no vacuum,
then there might be a break in the hose, a leak in the hose, a loose or
broken connection somewhere along the way, or a problem with the vacuum
pump. I'd follow the hose to it's source to determine the cause of the
problem. If there is one, fixing it should make the recirculate flap open
and probably will fix the air flaps as well.

If you do feel a vacuum, the problem is more likely to be electrical (yes,
the actuator switch could be broken, but that wouldn't explain the failure
of the air flaps.) Two wires lead to the vacuum switch, one black-blue and
one black-brown. The plug is polarized so it cannot be inserted incorrectly.
When +12VDC is applied to the switch, the vacuum is connected to the vacuum
cylinder, the arm moves and the flap opens. By the way, the flap is behind
the large black plastic box that houses the heater and A/C. You can feel it
by reaching behind the box. If you lie on your back you can see the flap.

Remove the wire plug from the vacuum switch. Start the engine and activate
the recirculate function. Test the voltage across the pins of the plug. It
should be +12VDC. Note that the recirculate icon (the little car) must stay
on when you push the button. If it goes off immediately after you push the
button, the car is forbidding you to use recirculate mode. You can only use
recirculate when the A/C compressor is on (the snowflake icon is lit). It
shuts off (and can't be turned back on) when the ambient temperature is
below about 40F. Assuming you can get the recirculate button to stay on, and
you don't measure +12VDC at the plug, something is wrong with the climate
control computer or electrical system. That I can't help you with.

By the way, you can get to the vacuum switch a little more easily, and see
things better, by removing the glove box. To do so, open the box, disconnect
the two wires on the glove box light, and remove the four bolts at each
corner. Remove the plastic strip with the rubber stop on both sides, and
squeeze the box to one side to free the hinges (i.e., horse the darned thing
out of the opening.) This is not really necessary, but allows you to get to
the vacuum switch without lying on your back.

Good luck.

Dick Green

>Anyone familiar with trouble shooting the 93 model year automatic
>climate control system?  Mine worked excellent until it seemed to loose
>control of the air flaps.  The system no longer sends air to the dash
>defrost vent when asked to, nor does it close the recirculate flap on
>command.  I know climate control problems are very rare in late model
>Audis (ha, ha).  Again, I think this is an electrical problem with the
>system rather than a mechanical fault.  How do you even remove the
>system from the dash?  I can't find a way to access the screws or clips
>which hold it in place.