[s-cars] A/C shutting down

[Bob Rossato]

I'm not so sure it's the engine overheating as much as the AC system
pressures being high, or at least the sensors thinking it's high.  The
engine cooling system on these cars is more than up to the job.

I too have had the AC shut down on me, but only when first starting the car
after it's been sitting in the parking lot on a hot day.  I've had it happen
a handful of times when going out for lunch.  Ambient temps are typically in
the mid-90s and up.  AC will shut off a few seconds after I start the car.
Immediately pushing the AC button does nothing.  Continue on and try AC
button again after 30-40 seconds and it starts back up but then shuts down
after a few seconds again.  Repeat wait cycle and this time it holds.  By
the time I'm out of the parking lot it's holding and never acts up again for
the rest of the trip.  I've never had to drive the car in stop and go
traffic so I don't know if it would start acting up again in that situation.

>From my review of the Bentley manual a while back on this issue, I found the
following three sensors that would shut down the compressor:

F73 A/C Refrigerant Low Pressure Switch - Switches A/C clutch OFF if system
suction pressure is too low (low refrigerant charge)

F118 A/C Refrigerant High Pressure Switch - Switches A/C clutch OFF if
system pressure is too high

G111 A/C compressor Speed Sensor - Determines A/C compressor speed; compares
compressor speed to engine speed and calculates belt slippage and switches
compressor OFF if slippage is too large (for example, if belt is too loose.)

Since I'm just starting the car after it has been sitting for 4-5 hours,
engine temperatures are not an issue in my situation.  I think it's just the
high pressure switch on the AC system that is doing it.  Whether it is
because the pressures are truly high and the system is trying to protect
itself, or the high pressure switch is just overly sensitive I don't know.
But my money is on the latter.  Sensors do drift with age.  That in
combination with the higher baseline pressures as a result of the car baking
in the hot sun could be enough to trigger it.

Might be worth changing that out and see if you continue having problems.

Bob

> -----Original Message-----
> From: s-car-list-bounces at audifans.com
> [mailto:s-car-list-bounces at audifans.com]On Behalf Of Mike Claire
> Sent: Friday, July 23, 2004 6:50 PM
> To: TOM GREEN; s-car-list at audifans.com
> Subject: Re: [s-cars] A/C shutting down
>
>
> Thanks Tom and other listers who replied.  In a
> perverse way I guess this is good news - nothing to
> fix!  But it still surprises me that a car can be
> designed without sufficient cooling to survive in even
> 110 deg temps without having to resort to shutting
> down A/C.
>
> One more question about these A/C systems.  The
> compressor is LOUD.  A constant groan kind of like a
> dry power steering unit.  Is this normal too?  I guess
> I hope it is...
>
>
> Mike