A/C Compressor Zener Diode to stop radio popping

urq urq at pacbell.net
Sat May 9 09:32:24 PDT 2009

.... sorry it took a while to get to this Ken,

I would recommend that you look into the "SA15A" transient suppressor,
manufactured by several sources ... Littelfuse, Fairchild ... 

I did a quick web search ... many places (like DigiKey) have an outrageous
minimum quantity ... far too many for even a group buy.  I did find a
retailer who would sell them individually for $0.69 and seem to be offering
a no minimum order sale ... 


I have never done business with this company, so I can't vouch for them ...
you may want to call them rather than placing an on line order.  They do
indicate they've been around a while, and they have an office in the USA.  

I may look into doing this mod on the V8s ... assuming they are prior to the
VIN break Scott mentioned.  If I do this I'll document it for others.  For
those DIYing this be aware that the device is directional 

You may want to look for one of the factory parts in a car in a wrecking
yard ... I doubt it would be something a person would specifically seek.

Your follow on question asked if the mod will work for other non-factory
stereos ... if you are hearing a pop when the compressor is switched the
answer would be yes, it will likely help you too.  Some stereos may do a
better job of filtering power transients.  The compressor clutch is the
source of the noise, it is a large inductive source, so when power is
applied and removed a transient is generated.  

HTH and IUD!
Steve Buchholz

-----Original Message-----

Does anyone know where I can find the appropriate Zener Diode to use
with the a/c compressor (patient is a 200q20v) to stop the feedback
popping when the clutch cycles?  I found some on Mouser.com but they
are sold by large quantities and I just need one.
http://www.sjmautotechnik.com says it needs to be one with an 18v
breakdown voltage.

Has anyone done the mod?  It's described here:



More information about the quattro mailing list