[s-cars] A/C update

[Tom Green]

My suggestion is to carefully inspect the serpentine
belt and tensioner to insure they properly tension
the belt and it does not slip.  You should not be able
to turn the belt without the engine and accessories
turning as well.  Maybe a mirror will allow inspecting
the crank pulley and damper.

Then remove the serpentine belt and check the clutch
and compressor.  I think you can engage the clutch
without the engine running and see if it holds when
turning the compressor and if the compressor turns
freely.

I would check the speed sensor and clutch wiring
and change the sensor before changing the
compressor if it turns freely.  This wiring is not far
from the headlight washer as well as below the
thermostat housing.

I don't think a professional audi shop or A/C shop
will have any shortcuts to diagnose your problem
any better than you can, but I would expect a bad
compressor diagnosis at the start.  And, if you have
any doubts when inspecting the compressor, the
safe way is change it.  HTH

Tom

On Oct 4, 2007, at 9:50 PM, james McCarthy wrote:

> 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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