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Old 08-09-2009, 08:01 PM   #1 (permalink)
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Question Car models with auto-off A/C??

So I was trying to figure out a way to make a switch that would turn off the A/C in my car while accelerating. That made me think about the Civics that have this feature built in - the A/C only runs while the car is idling/coasting/decelerating. So I was wondering what other models out there also run this way. Any input? Do you guys know of any others? Also, what specific years of the Civics have this?


Thanks!
Woody

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Old 08-09-2009, 08:30 PM   #2 (permalink)
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...a simple vacuum switch "Tee'ed" into the intake manifold should work, with the switch set to OPEN when the vacuum drops below a preset value (about 10-14 inches Hg), and being wired into the hot line to the A/C compressor clutch.

...thus, when the manifold vacuum is HIGH (idle, light cruise, etc.) the switch is CLOSED and the A/C compressor clutch will operate as normal. But, when the manifold vacuum is LOW (accelerating or heavy load (hills), etc.) the switch will OPEN and the A/C compressor clutch will be disabled (only the compressor is disabled, all other fans/etc. continue working as before).

...might want to look into also installing an suitably size RC-snubber circuit across the vacuum switch contacts, as the inductive "kick" from the A/C compressor can/will eventually "eat" the vacuum switch contacts.
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Old 08-09-2009, 08:49 PM   #3 (permalink)
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Well that does sound like a nice setup Old Tele Man

If I were to do it to my car, though, I think I'd do it a bit more... 'ghetto'. I'd probably put some kind of physical switch on the pedal itself, and wire it into the A/C button on the HVAC control inside the car. That way when the pedal is released completely, it will trigger the A/C switch to come on. This would also give you a nice indicator as to whether or not it's actually working, since the A/C selector has an LED light on it.

My only concern with this is that on some cars, when you put on the defrost setting, the A/C will come on no matter if you select it or not. If the car in question is setup this way, I believe your suggestion of wiring the switch into the hotline of the A/C compressor would work much better.

I'll admit your plan sounds much more professional, and would probably be the route to go if you wanted to do a good job with it

Edit: Another possible idea for the switch may be modding and using a 'wide open throttle' switch that are used with nitrous kits. One of these modded so the switch is closed when your throttle is completely closed may just do the trick as well. I'm not referring to one that mounts behind the gas pedal, but one that would go on the throttle body.
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Last edited by swoody; 08-09-2009 at 09:05 PM..
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Old 08-09-2009, 09:21 PM   #4 (permalink)
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Vortec chevrolet's can do this, with a PCM reprogram. LS1 Corvettes do it from the factory when you floor the gas pedal, and any 96+ S10/blazer/silverado/tahoe/etc can be set to shut off a/c whenever gas pedal is pressed greater than n%

As an example, I had my stock 2001 Blazer's engine computer reflashed by wait4meperformance.com to shut off a/c for 30 seconds whenever the throttle is >80% (and then re-engage the a/c even if throttle remains depressed >80%, not that I can think of many circumstances that would call for 30 seconds of heavy throttle like that) - I had a few other changes made in there of course as well, but that was the one relevant to this thread.
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Old 08-09-2009, 09:26 PM   #5 (permalink)
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...to paraphrase a Viet Nam era movie: "...ah-h-h, there's nothing like the smell of WD-40 and Duct Tape in the morning."...and, obviously, it's a Saturday morning.

Last edited by gone-ot; 08-09-2009 at 09:39 PM..
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Old 08-09-2009, 09:43 PM   #6 (permalink)
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Quote:
Originally Posted by Old Tele man View Post
...to paraphrase a Viet Nam era movie: "...ah-h-h, there's nothing like the smell of WD-40 and Duct Tape in the morning."...and, obviously, it's a Saturday morning.
Exactly

(notice my sig, too? )
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Old 08-09-2009, 09:45 PM   #7 (permalink)
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...exactly, in fact, it was your tagline that reminded me of that quote...and the "new" working components just naturally came to mind (ha,ha)!

...ie: a DIY moment!
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Old 08-09-2009, 09:48 PM   #8 (permalink)
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Quote:
Originally Posted by shovel View Post
Vortec chevrolet's can do this, with a PCM reprogram. LS1 Corvettes do it from the factory when you floor the gas pedal, and any 96+ S10/blazer/silverado/tahoe/etc can be set to shut off a/c whenever gas pedal is pressed greater than n%

As an example, I had my stock 2001 Blazer's engine computer reflashed by wait4meperformance.com to shut off a/c for 30 seconds whenever the throttle is >80% (and then re-engage the a/c even if throttle remains depressed >80%, not that I can think of many circumstances that would call for 30 seconds of heavy throttle like that) - I had a few other changes made in there of course as well, but that was the one relevant to this thread.
Thanks for the insight Hmm.... maybe my Camaro could do this as well. It's a 2000, and has basically the same LS1 as the Corvette, but I'm not sure about the PCM. Do you know any cars that do it from the factory, though (and for an MPG boost instead of a power boost)? Like I said, I think certain newer Civics do it, but I'm not sure what years or what other cars out there have this feature.
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Old 08-10-2009, 05:15 AM   #9 (permalink)
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Quote:
Originally Posted by swoody View Post
Do you know any cars that do it from the factory, though (and for an MPG boost instead of a power boost)?
Gen 1 Isuzu Troopers with the 2.8L GM V6 briefly disengage a/c when throttle increases a given % - there's a "map" (as in, graphical representation of numerical plots) in the factory service manual for 1990-91 v6 troopers - but I think in their case it's for power since they're relatively short on it (120hp in a 3800lb brick)

I'm sure other cars must do it, since 2 of the cars i've owned do (or can) - i couldn't speculate on the exact reasons but the effect certainly is more useable power.

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