[s-cars] A/C update

Tom Green trgreen at comcast.net
Thu Oct 4 12:09:05 PDT 2007

I'm not sure from reading your previous posts that the troubleshooting
of this problem has followed an orderly course.  My understanding is
that the electric engine cooling fan does not come on when the A/C is
engaged and the A/C compressor clutch disengages in a very short
time afterward. (2 seconds?)

You have bypassed the turbo afterrun switch and the radiator temp
switches and the fan runs.  ( Since these switches are not part of the
A/C problem, no further investigation was conducted on the condition
of these switches).

Now, trouble codes show 01270  N25(clutch) speed deviation too high,
showing a difference between compressor rpm and engine rpm.

This probably means the fan just has not had an opportunity to come on
since the A/C shuts off so quickly, so we think the clutch switch  
will turn
the fan on.

Bentley has the causes, symptoms, and corrective steps for this problem.
Runs from serpentine belt too loose, control head not coded correctly  
likely) slipping clutch, binding compressor, or crankshaft vibration  
of incorrect diameter- MAYBE BROKEN LOOSE.

Several possible causes here are serious problems some even if you don't
use the A/C.  Check that pulley out on the crankshaft for damper  
Darin did have some photos on s-cars.org of a separated damper.

Perhaps you are lucky enough that the serpentine belt tensioner is not
holding tension on the belt or the belt is worn for an easy fix, or a  
not too bad if you get it before the tensioner grenades into the fan and
radiator and maybe timing belt.

If the compressor is binding, it is failing and probably making metal  
needs to be replaced before operating or you risk contaminating the  
system with metal-- think replacing condenser, evaporator, dryer,  
hoses, valves, no just replace the car.  Many Audis have wound up at the
salvage yard for this problem since the repair cost can approach the  
of the car.

Sounds pretty grim, but may be a simple fix, only you are there to  
find out.
A Bentley manual would help.


> Date: Thu, 4 Oct 2007 08:27:39 -0700 (PDT)
> From: james McCarthy <jjssmccarthy at yahoo.com>
> Subject: [s-cars] AC update
> To: s-car-list at audifans.com
> Message-ID: <620752.96416.qm at web52608.mail.re2.yahoo.com>
> Content-Type: text/plain; charset=iso-8859-1
> Thanks for the suggestions.
> It's hot here so not an ambient temp issue.
> Where is the code I get from the ProDiag:
> 01270 A/C clutch - N25 speed deviation too great.
> Any chance I don't need a new compressor?  the serp
> belt seems fine.
> tia
> -jamie


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