[s-cars] A/C update

[james McCarthy]

Tom,

I have a bently - thanks.

As for the order of the aproach - seemed reasonable as
when the ac failed on my avant - it turned out to be
due to an electric fan failure due to a wiring short
under the headlight washer hoses behind the driver
side headlight. Not to mention that it's super easy to
check these things without getting dirty.

As for the current issue -I guess I was hoping for
some help sorting out which of the bently list to look
at first...

Compressor seems most likely as I had never heard of a
damper failure - the search function on s-cars.org is
so poor that I can't find it there.

The belt doesn't apear to be slipping and the pully
seems to be spinning freely.  When the ac button is
depressed - the pully briefly engages and then cuts
out.  I've now determined that the fan is starting up
as well - but both quit 2 seconds later.

So - how best to figure this out.
I'll plod through it unless the list can offer some
suggestions as to how to proceed.
-jamie


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  
(not
likely) slipping clutch, binding compressor, or
crankshaft vibration  
damper
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  
condition.
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  
clutch,
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  
and
needs to be replaced before operating or you risk
contaminating the  
entire
system with metal-- think replacing condenser,
evaporator, dryer,  
compressor,
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  
value
of the car.

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

Tom


       
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