A/C on , rpms low
08-01-2005, 11:08 AM
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A/C on , rpms low Lately as the heat is unbearable, I've been running with my AC on. Whenever the compressor cycles on, there is a significant drop in rpms. my car is a M6 and its almost to the point of stalling out even with the clutch all the way in. has anyone had this problem. my cars got 48k on it. could it be a bad compressor? do they all do this? Usually idles at 8-900 rpms, when the compressor cycles on, it drops to around 5-600. Its seems like its putting too much of a load on the motor. Thanks.
-Jeff
-Jeff
08-01-2005, 10:06 PM
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Hmmm, funny, mine is a A4 and mine idles up higher (1100-1200), i hate it! i cant hear the lope of my cam! 
maybe there is a way to tune it to get it to idle up higher when A/C is on.
maybe there is a way to tune it to get it to idle up higher when A/C is on. 
08-02-2005, 06:36 AM
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Originally Posted by mxmccarter2401
ruined that car
Yeah because that's the answer to the question he asked
I don't have a M6 but in my car the idle drops when the compressor kicks on. It'll drop a few hundred rpm's for a second or two.
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08-02-2005, 07:39 AM
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Originally Posted by Frosty
Yeah because that's the answer to the question he asked
I don't have a M6 but in my car the idle drops when the compressor kicks on. It'll drop a few hundred rpm's for a second or two.
I don't have a M6 but in my car the idle drops when the compressor kicks on. It'll drop a few hundred rpm's for a second or two.
08-05-2005, 11:49 PM
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The IAC should compensate for the extra load right before the compressor kicks on. May be worth pulling off and cleaning. What is the charging voltage when this all happens?
08-12-2005, 08:09 AM
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mine does this at idle but only when the a/c and radiator fans are on at the same. (when its 80 degrees or higher). i have an a4 and it usually idles around 900-1000 and voltage around 14v. when the a/c is on battery reads 13-13.5 volts. as soon as the radiator fans comes on, rpms drop to about 700-800 and voltage to about 10-11v. one time it almost stalled but i revved the idle back to 800 at a stop light.
will keeping the rpms around 800-900 (gas while holding the brake down)at a stop light cause problems? i already replaced the alternator with a 180 amp and i also have an optima redtop.
can you explain what changes when you get this done to the pcm? will an overdrive pulley help? thanks.
will keeping the rpms around 800-900 (gas while holding the brake down)at a stop light cause problems? i already replaced the alternator with a 180 amp and i also have an optima redtop.
Originally Posted by WILWAXU
You can have the "A/C on idle" changed with tuning.
08-12-2005, 08:22 AM
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Originally Posted by Z_twenty_Jeff
Lately as the heat is unbearable, I've been running with my AC on. Whenever the compressor cycles on, there is a significant drop in rpms. my car is a M6 and its almost to the point of stalling out even with the clutch all the way in. has anyone had this problem. my cars got 48k on it. could it be a bad compressor? do they all do this? Usually idles at 8-900 rpms, when the compressor cycles on, it drops to around 5-600. Its seems like its putting too much of a load on the motor. Thanks.
-Jeff
-Jeff
When the air con pump kicks in and the clutch engages it will put load on the engine, maybe around 15bhp is required to turn the pump over. Usually a cars (not specifically Fbody just general) rpms will did when the air con kicks the PCM should then usually compensate and bring the rpms back up.
Similar things can happen with eletric cooling fans or even large stereo's with amps and subs, they will all increase load on the engine.
You could always fit a bigger alternator, but this will require more power to produce the same output, so it will need the engine idle speed altering.
If you've modded your car (even a lid or exhaust) it may be enough to effect the idle. Usually modern PCU controlled EFI engines can sort it out them selfs but not always and it depends what has been done.
The car should not stall however.
I'm guessing that the 'A/C on idle' PCM change would disable the air con from activating at idle. Remeber if you're stuck in traffic on a hot day this means your air con won't work until you pick up speed.
Personally if you want air con, leave it alone. If you're just gonna mess with it, take it off instead. All or nothing, anything else will never be quite good enough.
