Automatic A/C Shutoff?

A peculiar thing happened last week with the air conditioner in my 2004 330i (4-door, manual, with performance package). It happened while I was driving up the Grapevine. For those of you who don’t live in the Los
Angeles basin (or travel to it from the North), the Grapevine is a very long, very steep hill (heading South on Interstate 5) that climbs into the Tehachapi mountains which separate the Los Angeles basin from the central valley. I don’t know exactly how long or how steep the Grapevine is, but it seems to go on forever. Trucks have a special lane where they can be seen creeping up the hill at what looks like about 10 mph. I was in either 4th or 5th gear moving at about 80 mph. The temperature was about 85 degrees. The engine was not laboring at all (why should it?), and I could have easily increased the speed if I had wanted to. What happened was that part-way up the hill, the air conditioning shut off. After I crested the top of the hill, the air conditioning turned back on. This behavior had never happened previously in this situation, nor have I experienced this with any previous 3-series BMW that I have owned. I would be interested to know if the engine electronics in the newer cars have some special mode where the air conditioning is shut down when it is sensed that the engine is having to work harder than usual (i.e., climbing a long steep hill).
Lou D'Amario
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Lou,
I would say that you car is suffering from the traditional "Final Stage Resistor " problem. The hill was coincidental, try googling for "Final Stage Resistor" and all will be revealed!
Roger (a fellow sufferer).
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All AC systems will shut down if the pressure gets too high - and this is likely to happen at slow speeds where the condenser isn't being cooled properly.
Has your model an auxilliary cooling fan and is it working?
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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wrote:

But Dave, he said he was doing 80 mph, surely this is not slow speed travel.
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wrote:

Might have iced up, alternatively he may have been in a lower gear, so a long haul at higher revs...
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wrote:

Nothing ices up in Los Angeles in August.
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R. Mark Clayton wrote:

wrote: </pre> <blockquote type="cite"> <pre wrap="">I would be interested to know if the engine electronics in the newer cars have some special mode where the air conditioning is shut down when it is sensed that the engine is having to work harder than usual (i.e., climbing a long steep hill). </pre> </blockquote> <pre wrap="">All AC systems will shut down if the pressure gets too high - and this is likely to happen at slow speeds where the condenser isn't being cooled properly.
</pre> </blockquote> <pre wrap=""> But Dave, he said he was doing 80 mph, surely this is not slow speed travel.
</pre> </blockquote> <pre wrap=""><!----> Might have iced up, alternatively he may have been in a lower gear, so a long haul at higher revs...
</pre> </blockquote> Why would a long haul at higher revs cause the a/c condenser to ice up? Also, assuming the a/c shut down was caused by some automatic protective reaction, what is the best strategy for climbing a long, steep hill: high speed/low revs, high speed/high revs, low speed/low revs, or low speed/high revs. I have to believe that a 6-cylinder BMW has the capability to climb a long hill without the a/c shutting down.<br> </body> </html>
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My 02 M3 shuts off the compressor through the ECU based on throttle position. Since my car is entirely "drive by wire" it might be different than other models. The idea is to allow max performance when needed, and probably also to avoid very high revs on the compressor.
Bob
wrote:

is
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That's common on many cars. Demand full performance and the AC shuts down. After all, you're unlikely to run at full throttle for long.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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wrote:

A 3 Series pulling Grapevine Hill at 80 is only turning something on the order of 3000 rpm. I seriously do not think the A/C is shutting down under these conditions because they planned it to.
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J Strickland wrote:

</pre> <blockquote type="cite"> <pre wrap="">My 02 M3 shuts off the compressor through the ECU based on throttle position. Since my car is entirely "drive by wire" it might be different than other models. The idea is to allow max performance when needed, and probably also to avoid very high revs on the compressor. </pre> </blockquote> <pre wrap="">That's common on many cars. Demand full performance and the AC shuts down. After all, you're unlikely to run at full throttle for long.
</pre> </blockquote> <pre wrap=""><!----> A 3 Series pulling Grapevine Hill at 80 is only turning something on the order of 3000 rpm. I seriously do not think the A/C is shutting down under these conditions because they planned it to.
</pre> </blockquote> I beleive I was in 4th gear, so the rpms had to be much higher.<br> </body> </html>
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wrote:
My 02 M3 shuts off the compressor through the ECU based on throttle position. Since my car is entirely "drive by wire" it might be different than other models. The idea is to allow max performance when needed, and probably also to avoid very high revs on the compressor.
That's common on many cars. Demand full performance and the AC shuts down. After all, you're unlikely to run at full throttle for long.
A 3 Series pulling Grapevine Hill at 80 is only turning something on the order of 3000 rpm. I seriously do not think the A/C is shutting down under these conditions because they planned it to.
I beleive I was in 4th gear, so the rpms had to be much higher.
I can't imagine why you feel you needed to be in 4th, your car can easily pull that grade in 5th doing 80. It youhad to downshift, then you have issues to deal with. Even in 4th, the tach should be hovering around 4 grand, hardly a load that should shut the A/C off even if the A/C was meant to shut itself down.
There are lots of freeway hills that are just as steep as the Grapevine. The Grapevine gets its distinction because it is so long, not because it is so steep. My car climbs equivelent grades with 4 adults crammed inside, and the A/C does not shut off.
PS, Please turn the HTML off before posting again.
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Yes - didn't read or comprehend the post fully. ;-)
And of course it depends what the OP meant by shutting down. If the blowers stopped running it's likely the usual final stage fault. If the compressor switched off - pass.
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Dave Plowman (News) wrote:

What I meant by "shutting down", was that the air coming out of the dash vents was no longer being cooled. From the other posts, it appears that shutting down the a/c is a normal occurrence when high demand is being put on the engine. I was just surprised, becuase I had never experienced this before.
--------------000406010805090505020707 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type"> <title></title> </head> <body bgcolor="#ffffff" text="#000000"> Dave Plowman (News) wrote:
<pre wrap="">In article <a class="moz-txt-link-rfc2396E" href="mailto:t snipped-for-privacy@ez2.net">&lt;t snipped-for-privacy@ez2.net&gt;</a>, Jeff Strickland <a class="moz-txt-link-rfc2396E" href="mailto: snipped-for-privacy@yahoo.com">&lt; snipped-for-privacy@yahoo.com&gt;</a> wrote: </pre> <blockquote type="cite"> <blockquote type="cite"> <pre wrap="">All AC systems will shut down if the pressure gets too high - and this is likely to happen at slow speeds where the condenser isn't being cooled properly.
</pre> </blockquote> </blockquote> <pre wrap=""><!---->
</pre> <blockquote type="cite"> <pre wrap="">But Dave, he said he was doing 80 mph, surely this is not slow speed travel. </pre> </blockquote> <pre wrap=""><!----> Yes - didn't read or comprehend the post fully. ;-)
And of course it depends what the OP meant by shutting down. If the blowers stopped running it's likely the usual final stage fault. If the compressor switched off - pass.
</pre> </blockquote> What I meant by "shutting down", was that the air coming out of the dash vents was no longer being cooled. From the other posts, it appears that shutting down the a/c is a normal occurrence when high demand is being put on the engine. I was just surprised, becuase I had never experienced this before.<br> </body> </html>
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wrote:
All AC systems will shut down if the pressure gets too high - and this is likely to happen at slow speeds where the condenser isn't being cooled properly.
But Dave, he said he was doing 80 mph, surely this is not slow speed travel.
Yes - didn't read or comprehend the post fully. ;-)
And of course it depends what the OP meant by shutting down. If the blowers stopped running it's likely the usual final stage fault. If the compressor switched off - pass.
What I meant by "shutting down", was that the air coming out of the dash vents was no longer being cooled. From the other posts, it appears that shutting down the a/c is a normal occurrence when high demand is being put on the engine. I was just surprised, becuase I had never experienced this before.
That is not true, the A/C should not shut itself down under the conditions you cited.
Even if it does shut itself down under load, you should not have loaded it enough just climbing Grapevine Hill. Indeed, downshifting into 4th should reduce the loading through the mechanical advantage of the lower gear.
My suggestion is to get A/C service. You could be low on R134a, and this can cause what you complained of.
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Right - that's clear. But the compressor shutting off only usually happens at full throttle.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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I once owned a Chevrolet that did this, but my BMW has never done it. I think you are having a service issue. Another poster suggest the resistor pack, I am inclined to agree with him.
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Next hot day, check the sight glass and see if there're bubbles. You might be low on refrigerant which could trip the low pressure switch when under a heavy load.

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