Thread: AC Compressor Engaging at Inapproporiate Settings

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  1. #1 AC Compressor Engaging at Inapproporiate Settings 
    SE Level Member kurthaver's Avatar
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    I recently joined the ranks with the purchase of a 2006 GT and have to say that this is the tightest, most enjoyable car that I have owned since my '89 525i (lost the intake valve on #6 and would have cost more to fix than it was worth...I learned my lesson).

    Anyway, my only complaint was the gas mileage...consistently 17 mpg with mixed city/highway driving. I had resigned myself to the fact that my enjoyment was going to come at the cost of additional fill-ups until I started it with the remote a few days ago and was close enough to hear the familiar click of the AC compressor engaging.

    Now, I am fairly certain that the AC engages in defrost mode, but I never leave the climate control parked there for that very reason. I suspected that it might be an automatic feature of the remote start in cold weather, so I did some testing and found that it also engages during normal keyed ignition and operation.

    The findings were that the AC compressor engages at all climate control settings except for the upper vent and mixed upper/lower vent settings. At no time, BTW, does the AC indicator light on the AC button illuminate. So, I have been driving for the last couple of days with the upper vents selected and I am magically getting 20mpg via the average that the car has calculated. Needless to say, I am a much happier camper and I guess the obvious question would be 'why?' Is this a common problem?

    Searches have yielded no mentions of this issue.
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  2. #2 Re: AC Compressor Engaging at Inapproporiate Settings 
    Killa Bee Scottydoggs's Avatar
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    my regal a/c compressor also comes on with any setting i put it on, hot or cold. im told its normal.

    what i do is i just pull the relay for the a/c every fall, (fuse box under the hood) that way it dont run at all, and mpg are not affected from it being on.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  3. #3 Re: AC Compressor Engaging at Inapproporiate Settings 
    SE Level Member volvo92906's Avatar
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    The A/C comes on in all defrost settings on ALL equipped vehicles.

    1) An A/C system removes moisture from air. This air is what you want to defrost (remove moisture) from a window.
    2) This a way to make sure yourcompressor works for the other 4-6 months of the year so it gets lubricated thoroughly.

    If you still dont understand why, here is a very lengthy article (using Audi) but it is still relevant.

    http://www.audiworld.com/tech/misc2.shtml

    -Volvo
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    Last edited by volvo92906; 11-24-2012 at 03:37 PM. Reason: Adding Information
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  4. #4 Re: AC Compressor Engaging at Inapproporiate Settings 
    SE Level Member kurthaver's Avatar
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    Thank you. The article was very informative, but I may not have been completely clear in my post.

    I actually do understand that the AC runs in defrost mode and that it can also come on periodically to manage cabin humidity when using auto climate control mode...that is by design.

    My issue is that the AC runs even when it is not in defrost mode or auto climate control mode. The only settings where the AC does not operate in manual mode is when full dash vents or the partial floor/dash vent mix are selected. As soon as I turn the knob to full floor/dash vent mix or full floor vent, the AC kicks on. None of these settings involve defrost. I could see if it kicked on with dash vents to possibly clear side windows, but this is exactly the opposite.

    I was looking to see if perhaps there was a known issue with this as I am pretty certain that this is not by design. If design dictated full-time AC, it would not operate in some modes but not others...and if full-time is normal, why have a switch.


    Quote Originally Posted by volvo92906 View Post
    The A/C comes on in all defrost settings on ALL equipped vehicles.

    1) An A/C system removes moisture from air. This air is what you want to defrost (remove moisture) from a window.
    2) This a way to make sure your compressor works for the other 4-6 months of the year so it gets lubricated thoroughly.

    If you still dont understand why, here is a very lengthy article (using Audi) but it is still relevant.

    AudiWorld Tech Articles

    -Volvo
    ASE Master Automotive Technician and Master Medium Heavy Truck Technician.
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  5. #5 Re: AC Compressor Engaging at Inapproporiate Settings 
    SE Level Member volvo92906's Avatar
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    Quote Originally Posted by kurthaver View Post
    The only settings where the AC does not operate in manual mode is when full dash vents or the partial floor/dash vent mix are selected. As soon as I turn the knob to full floor/dash vent mix or full floor vent, the AC kicks on.
    Ok, I think I may still miss the mark. I see that the only settings it does NOT operate in manual mode are those certain ones...

    You do have auto climate control, yes? Wet carpet/interior is a a cause for humidity and therefore can kick in the compressor on a vehicle that senses the climate. (Toyota Prius does this). So, I cannot say for certain but it is possible that this is what is happening. However, if your car has an 'Auto' button and you shut that off, it will not run the compressor.
    I wish they would let me put a strikethrough on this but I cant. I wanted to keep it up for the info, but after reading I dont think it has to do with the problem youre having.

    Is your A/C run using the computer? I wonder if something may be wrong with it? I thought I had more of an idea but seeing as to how you say it runs in other settings on manual mode, that doesnt sound right. I couldnt see any way that could be possible without being a computer controlled system, and even that is pretty out of the ordinary. Or, maybe there is something I dont know. I have a 2005 GT, although I am unaware of the differences in the cars, I did not see anything on TSB's about a/c system performance so it must not be a known problem. I will see if maybe I cant find out more information sometime in the coming week.
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  6. #6 Re: AC Compressor Engaging at Inapproporiate Settings 
    Killa Bee Scottydoggs's Avatar
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    like i said, you dont have a problem, they all do this. its normal. and for all the reasons volov has given, hes right on track with his posts and why the a/c is on.

    if you dont want the a/c compressor to come on, pull the relay, a whole bunch of do it every fall.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  7. #7 Re: AC Compressor Engaging at Inapproporiate Settings 
    Former GP Owner Chadgervais's Avatar
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    I am thinking about pulling my AC relay, couple questions: Will the defroster still be effective? Will the cooling fans still come on if I push the AC button, in other words, does the relay just kill the compressor or the whole circuit?
    FORMER GRAND PRIX OWNER- NO LONGER ACTIVE ON GRANPRIXFORUMS.NET
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  8. #8 Re: AC Compressor Engaging at Inapproporiate Settings 
    Killa Bee Scottydoggs's Avatar
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    it kills the power to the a/c compressor, the defroster works just fine, as do all of the other settings.

    the fans work as they normally would, off the temp sensor.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  9. #9 Re: AC Compressor Engaging at Inapproporiate Settings 
    SE Level Member volvo92906's Avatar
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    ''a/c controller is the most probable cause. You can hook up a scan tool and see if there is a command for the a/c to kick on under those settings. If there is, it is not working properly and should be replaced.''

    That is coming from a guy at work who was a GM dealer technician for 30+ years.
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