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Re: '91 200Q: no air from dash vents

Here's an old post, for the 5kq.  Sounds like a similar problem, hope this 
chris miller, windham nh, c1j1miller@aol.com

Date: Sun, 21 Sep 1997 20:47:13
From: Tony Lum <tlum@flash.net>
Subject: A/C Programmer-another fix! (kinda long)

Hi fellow listers,

Today's lesson is how to fix your A/C programmer to blow cold air on you
and NOT your window!  First of all you gotta have a hand vacuum pump-it is
essential for testing.  Second you can't have any electrical problems in
the control head-in other words the readout on channel 01 is "00" (no
faults found).  This fix involves the solenoid actuated vacuum valves.

I had the typical symptoms on my '87 5kTQ, A/C blows nice and cold and into
the windshield! Rather than surrender $125 on a used programmer from Dad's
in Rancho Cordova, I decided to really dismantle mine first (if I destroyed
it THEN I could justify the long drive).  Since my control head was showing
no faults on channel 01 and channel 07 was displaying that the head was
outputting the correct signals, the problem had to be in the programmer.
After removing the programmer, I examined the PC assy very closely for
solder failures but I could find none. Also found no oil in the vacuum
lines.  I could hear the solenoids click as I pushed the various buttons on
the A/C control head so the electrical control signals were working.  I
then completely removed the entire solenoid assembly complete for testing
and here is where I made some interesting discoveries.

I tested each vacuum valve using my hand vacuum pump for operation and they
all worked when I applied 12 volts.  The discovery was what happens when
the power is removed.  With the vacuum applied to the center inlet nozzle,
the valves for center vents (yellow line) and recirculation door (red line)
would consistently leak very quickly when power was removed.  Aha says I!
So I whipped out my junker controller that I got for $8 hopeing to use for
this car.  Unfortunately the '85 programmer is different from the '86 on
programmer.  But it does have 4 vacuum solenoids, so I tested those too and
guess what-the same 2 solenoids leak too.  All that "heavy" vacuum must
wear out the seals in these valves.  So taking the best 2 (lowest or no
leakage) valves, I replaced the center vent and recirc valves, put the
whole thing back together and the A/C system works just like it was factory
new! If you don't have some "spare" vacuum valves, you can probably swap
the bi-level valve (green line) or the floor vent valve (blue line) but if
yellow and red valves are leaking bad, you're still gonna lose vacuum.

BTW, now I understand why plugging the red line sometimes restores A/C
operation for some listers.  This is the line to the recirculate door
vacuum motor and its common for the bracket for this motor to break off its
mounts which will pull off the vacuum line and cause a leak. Plugging this
line will stop the leak, but disable the recirculation door and impair the
cool down speed of the system.  Also this line inside the evaporator is
exposed to the elements and can dry out and crack.  Mine is cracking and I
intend to replace it when I get the factory bracket kit used to fix this
problem. Kudos to Steve Bucholz who documented this problem! 

Now I can drive the big TQ when it gets hot now and not suffer to much :-))

Stay cool,



Tony Lum
Fremont, California, USA

Audi Owner/Operator/Mechanic by Necessity ;-)

1987 5000S Turbo Quattro
1985 4000CS Quattro
1980 5000S Sedan