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Old 12-13-2011, 07:58 AM   #1
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A/C Deactivation under hard acceleration?

There is this big car guy and fellow engineer I work with who has owned a 1991 911 and now drives a 01 BMW 5 series and a Lexus SC400 he brought back from the dead and modified.

He says that some cars have this feature where the A/C turns compressor turns off automatically under hard acceleration so that it does not take any power away from the engine. He said his BMW and Lexus came with that technology, and that he installed that feature in another car of his in the past. He said it is a simple wiring modification I can buy.

Have any of you heard of this "Part-time underdrive pulley-like modification"? Do our 986's already have that feature?

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Old 12-13-2011, 09:33 AM   #2
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Even my old SAAB 900-94 had this feature so I guess more or less every car has it.
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Old 12-13-2011, 10:05 AM   #3
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I believe it's function is to preserve the integrity of the compressor, not to return power to the engine, even my truck does that.
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Old 12-13-2011, 11:36 AM   #4
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Interesting. So there is no point in turning off my A/C in a drag race.
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Old 12-13-2011, 12:31 PM   #5
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AC on always robs power, in an old V8 truck, not a big deal, in a sports car it's always a big deal. My understanding is the compressor has a clutch like apparatus to kick itself out of an over rev situation, but as soon as you lift up or back off it usually comes right back on.
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Old 12-13-2011, 12:34 PM   #6
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Quote:
Originally Posted by ProjectM96 View Post
Interesting. So there is no point in turning off my A/C in a drag race.
You could install a custom circuit that cuts off the compressor during full throttle or you could just push the snowflake button on your dash. Job done.
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Last edited by Topless; 12-13-2011 at 12:36 PM.
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Old 12-13-2011, 05:10 PM   #7
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Back in the '90s, I remember buying a switch that was activated by vacuum (adjustable) and it would cut off the a/c compressor if it senses that you are going full out... It was a simple install (at least on a front engine jap car) and it does work (I think... but I got it installed on a puny 4 cylinder engine... ha ha). It just got hot in the cabin if you continue to drive aggressively...

It eventually went on full compressor cut off mode so I removed it.

Last edited by shlim8; 12-13-2011 at 05:14 PM.
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Old 12-13-2011, 08:40 PM   #8
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From the User Manual, page 116:
General instructions for air conditioning compressor
- Can switch off briefly if engine is under an extreme load to ensure sufficient engine cooling.

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