A/C Compressor Zener Diode to stop radio popping

Henry A Harper III hah at alumni.rice.edu
Thu May 7 10:27:54 PDT 2009

> On Thu, May 7, 2009 at 12:52 PM, Henry A Harper III
> <hah at alumni.rice.edu> wrote:
> >> Thanks Kneale.  Do you, or does anyone reading, know whether this is
> >> only required/helpful with the factory sound system or is there/would
> >> there be popping with aftermarket components as well?
> >
> > I don't think I have ever heard any popping from the a/c
> compressor on the
> > 12 year old aftermarket system in my car (Kenwood CD head +
> outboard amps).
> > So I vote for Bose-only issue.
> It's not a "bose-only" issue, and not all cars are affected, because
> in some, they already have the diode.  On the 200q20v there was a
> recall to REPLACE (or install?  I forget which now) the diode.  It's
> called inductive kickback:
>...and the cause is the A/C compressor clutch's electromagnet.  The
>pop noise is from a large voltage spike.  If you feel comfy plugging
>your GPS/iPod/etc into the cig lighter with those spikes, be my guest
>:)  It's a cheap fix...

All right, I change my vote to "does not affect my car, for whatever reason"
then. As I said, it's had the same Kenwood CD head unit for 12 years now -
apparently undamaged by all these large voltage spikes. I'm unmotivated to
change it to a more iPod-friendly unit if it's not broken and the FM
transmitter option barely works so no worries about plugging in my
iPod...and I have had the same 10 CDs in the changer for about the last 6
years...good mix.

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