[s-cars] Engine Management shuts off AC?

Wed Jul 27 20:19:43 EDT 2005

This AC system is nuts. Typical german. -short vent right there.
There are about 11 ways that can shut off your AC. From looking in my
bentley cd, diagnostic channel 52 has the following reasons to shut
down. (abbreviated)
A1: Slippage or blockage, refrigernat high pressure switch 120x
B1: rpm<200-500rpm
D1: rpm > 6000rpm
B2: low voltage
C2: kick down switch (From trans controller)
D2: Engine Coolant Temp warning light switch -I guess this is from the
MFTS
E2: Low pressure switch 
F2: High pressure switch
C3: Outside temp too low
D3: Engine management system (My personal fault code)
F3: ambient temp at blower <27f

So low voltage will be shown by segment B2
The MFTS fault, which also effects the dash guage will be shown by
segment D2
I still haven't used a VAG to find out what causes D3, but hope to do
that soon.
My opinions on Keith's q's:

>As the three of us have S6's, can you guys comment on your (yes its
>unreliable) voltage gauge behavior?

-My gauge says a pretty steady 14 (if the mark between 12 and 16 is 14)
It will drop to about 13 at night with the fan motor blowing at a good
speed, but seems like my voltage is reasonable. 

>Could a low voltage situation be clouding the operation, output, or
>interpretation of the MTFS signal perhaps, causing the AC to be
>disabled in abnormal circumstance?  Could a low voltage situation
cause the fan to run backwards?

>Is it possible to get hot air pockets in the coolant system, perhaps
>near the temperature sender that drives the dash display? (which might
>explain the rapid temperature changes that I saw...)

I hear the MFTS can fail intermittantly, which will cause the temp gauge
to jump up and down. That is more likely in my opinion to be the cause
of crazy MFTS function rather than voltage. I don't think hot pockets in
the cooling system are the culprit. The fan has 2 speeds, it could be
the speeds were reversed somehow...

I can barely hear my fan though. I thought for a long time it didn't
work, until I really listened for it.

Ah, recreational speculation, Best to use some diagnostic equipment and
figure it out....
Cooler times ahead,
Mike

-----Original Message-----
From: Keith Maddock [mailto:keith.maddock at gmail.com] 
Sent: Wednesday, July 27, 2005 5:18 PM
To: Bob DG
Cc: Toborg Michael (AC-SM/ESC3) *; TMULLANE at snet.net;
s-car-list at audifans.com
Subject: Re: [s-cars] Engine Management shuts off AC?

Just before the 2nd Rodknocking incident, I was having similar issues.

I also beleive I was having low voltage issues due to bad ground
between the alternator and vehicle ground.  (most likely a re-assembly
error when putting in the engine).

The AC would stay on as long as I was driving "normally", but after a
couple of full boost runs, it would disable.

Also weird was that I noticed some odd engine temp behavior related to
the AC before it would shut off.  Idling in traffic, turning the AC
would cause the engine temps to go from the thermostat point to the
"turn on all the fans full blast point" in approx 10 seconds.  turning
the AC off resulted in a nearly same-speed return to the thermostat
point.

I was almost convinced the electric radiator fan had been plumbed
backwards and was pulling hot air into the radiator when turned on. 
But when I got home I used a postcard to verify that the fan was
indeed pulling outside air through. Then again, I also could not
duplicate the same temperautre behavior, and I didn't stay testing too
long because there were some very familiar and very expensive sounds
eminating from the depths of the block...

As the three of us have S6's, can you guys comment on your (yes its
unreliable) voltage gauge behavior?

Mine would start around 13.7v at startup and eventually run down to
12V after the engine got warmed up over 20 minutes or so.   (which
goes back to the ground issue being temperature related).

Could a low voltage situation be clouding the operation, output, or
interpretation of the MTFS signal perhaps, causing the AC to be
disabled in abnormal circumstance?  Could a low voltage situation
cause the fan to run backwards?

Is it possible to get hot air pockets in the coolant system, perhaps
near the temperature sender that drives the dash display? (which might
explain the rapid temperature changes that I saw...)

More questions than answers, sorry....

Cheers,
Keith

On 7/27/05, Bob DG <bobs6 at msn.com> wrote:
> Yes, only when car is hot.
> 
> >From: "Toborg Michael (AC-SM/ESC3) *" <Michael.Toborg at us.bosch.com>
> >To: "Bob DG" <bobs6 at msn.com>, <TMULLANE at snet.net>
> >CC: <s-car-list at audifans.com>
> >Subject: RE: [s-cars] Engine Management shuts off AC?
> >Date: Wed, 27 Jul 2005 08:20:02 -0500
> >
> >Does your AC stop working only when the car is hot? Mine gets
shutdown
> >by the engine management even when the car is cold.
> >
> >MT
> >-----Original Message-----
> >From: Bob DG [mailto:bobs6 at msn.com]
> >Sent: Tuesday, July 26, 2005 7:17 PM
> >To: Toborg Michael (AC-SM/ESC3) *; TMULLANE at snet.net
> >Cc: s-car-list at audifans.com
> >Subject: RE: [s-cars] Engine Management shuts off AC?
> >
> >I have the same problem, though it is related to the electric rad
fan,
> >intermittently works- even when ac is off. coolant heats up when
idling
> >in
> >traffic...
> >
> > >From: "Toborg Michael (AC-SM/ESC3) *" <Michael.Toborg at us.bosch.com>
> > >To: <TMULLANE at snet.net>
> > >CC: s-car-list at audifans.com
> > >Subject: RE: [s-cars] Engine Management shuts off AC?
> > >Date: Tue, 26 Jul 2005 10:02:01 -0500
> > >
> > >Hmm, I hear this limits boost also. Hope I can fix my AC and get
some
> > >extra power. That would be nice.
> > >-Mike
> > >
> > >-----Original Message-----
> > >From: TMULLANE at snet.net [mailto:TMULLANE at snet.net]
> > >Sent: Tuesday, July 26, 2005 11:35 AM
> > >To: Toborg Michael (AC-SM/ESC3) *
> > >Cc: s-car-list at audifans.com
> > >Subject: RE: [s-cars] Engine Management shuts off AC?
> > >
> > >Sounds like a bad MFTS (multifunction temp sensor).
> > >One of its jobs is to prohibit the AC from coming on
> > >if engine temps are too high.  The sensor is located
> > >in the water manifold just above the thermostat.
> > >
> > >Tom
> > >
> > >Date: Tue, 26 Jul 2005 07:57:11 -0500
> > >From: "Toborg Michael (AC-SM/ESC3) *"
> > ><Michael.Toborg at us.bosch.com>
> > >Subject: [s-cars] Engine Management shuts off AC?
> > >To: <s-car-list at audifans.com>
> > >Message-ID:
> > ><18CC350E919CE04A831B9CCE2B88700643552C at sbdmail09.us.b
> > >osch.com>
> > >Content-Type: text/plain; charset="us-ascii"
> > >
> > >Still sweating in my 95 S6...
> > >Used diagnostic channel #52 yesterday to try and
> > >figure out why the AC
> > >doesn't work, and I got segment d3 to light up.
> > >Bentley says this is
> > >"Engine management system" It pretty much turns off
> > >the compressor as
> > >soon as it comes on. When driving I can feel a slight
> > >hesitation when
> > >the compressor cycles... The electric fan seems to be
> > >working fine.
> > >
> > >So what does this code mean? What part of engine
> > >management system is
> > >shutting off the AC?
> > >I gues a VAG tester might be the next tool to use...
> > >
> > >Thanks!
> > >
> > >
> > >
> > >_______________________________________________
> > >S-CAR-List mailing list
> > >S-CAR-List at audifans.com
> > >http://www.audifans.com/mailman/listinfo/s-car-list
> >
> >
> >
> 
> 
> _______________________________________________
> S-CAR-List mailing list
> S-CAR-List at audifans.com
> http://www.audifans.com/mailman/listinfo/s-car-list
> 

-- 
------
PGP Key: http://keith.maddock.com/pgpkey.html