[200q20v] Bose intermittent pops

[Kneale Brownson]

Scott Mockry documents this on his website under "click or pop heard when 
A/C turns on,,,"   What happens is the magnetic clutch for the A/C sends a 
shock to the ECU because of some fault in the design.  Usually you just 
hear the pop on the radio initially, but as time goes on, you start getting 
a violent jerk in the operation of the vehicle.  The fix from Audi, based 
on a TSB Group 87 #92-02,  is to install a small wiring harness in the 
wiring to the A/C clutch that includes a zener diode and replace the A/C 
clutch relay under the dash with a modified one.  The relay is Part # 
443-919 578H  and the zener diode wiring harness kit is part # 443-298-008 .

I installed these two items, which cost something over $100.00  at a 
"discounted" price from Carlsen.  The two items are dealer-only products, I 
was told at the time.

The installation amounts only to separating a connector set on your A/C 
wiring that's easily available in the engine compartment, inserting the 
"harness", which has appropriate wiring connectors to go into that 
junction, grounding the diode and applying a tie-wrap to hold the excess 
wire.  The relay goes into the panel behind the lower dash panel below your 
steering wheel.  It's a bit of a trick to figure out which relay is which 
(the diagram on the back of the panel is pretty unreliable and half the 
relays have their part numbers on a side that can't be viewed until you 
pull them out), but it's no biggie.

The more wiring-adept may be able to modify the original relay to provide 
the same protections.  I was told to simply replace the burned diode in the 
relay, but I couldn't see any sign of a burned/blown diode and have no 
facility for checking each diode in the relay, so I opted for the fix Audi 
prescribes.

At 05:53 PM 06/13/2001 -0500, Steve Crosbie wrote:

>Guys,
>    Started getting intermittent popping from Bose unit in my '91 200 last 
> winter.  Appeared to be related to high humidity days.  Thought it was 
> the incendiary device on wheels syndrome - our rear speakers.  I just 
> discovered that when I turn off my air conditioning (auto mode) the 
> popping stops (AC blowing cool at best - appointment tomorrow ... 
> hopefully just a low charge). It appears to pop after the clutch on the 
> AC compressor is released.  Is there a fix for this ... an electronic 
> filter gone awry?  I seem to remember a post that was related to the AC 
> system and radio problems, but couldn't find it. Thanks,
>Steve
>
>'91 200
>'97 A4 1.8
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