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Thread: Baffling Automotive A/C question-NEVER found an answer

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    Member Barrett's Avatar
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    Baffling Automotive A/C question-NEVER found an answer

    Realizing this isn't even remotely germane to anything motorcycle related....i thought i'd access the automotive-world brain power on here for possible answer. even local Chrysler/Toyota dealer gurus couldn't answer it. so here goes.
    in my fleet is a low mileage 2006 Dodge Dakota Club cab with SOHC 4.7 magnum V-8.
    question also applies to my 2007 Toyota Yaris sport coupe.
    both have nearly identical heater and a/c controls. on the control pod area for both is blower motor speed knob...temp adjustment knob....outside/recirculate control knob...and most importantly small button you push IN to activate the a/c system which seems to directly turn compressor on and off. it illuminates when pushed in.
    when i'm driving either vehicle on hot day i set controls as follows: temp knob to max cool...other knob set to recirculate...fan speed knob to high...and push the a/c button IN. result on both is nice icy cold a/c air.
    when the temp gets comfortable i reach over and press the a/c button which turns off the compressor but everything else remains the same. then when it heats up inside again, i push button back IN and cools off.
    PITA on trips, as you can imagine. but doing this does give the compressor a rest.
    here's my question: if i set everything as above...leave a/c button pressed in...then adjust temp knob for nice comfortable cabin temp....does it keep the compressor running constantly? or cycle the compressor ON and OFF? as mentioned, even local dodge and toyota guys don't know.
    THANKS MUCH!

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    The compressor always runs when you have ac on. Turning the control temp knob on most vehicles will open a damper to allow warm air from outside to mix with the cooled air. But i dont know how all the models work. Some have clutches some dont.

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    Senior Member 34nineteen's Avatar
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    Quote Originally Posted by Barrett View Post
    Realizing this isn't even remotely germane to anything motorcycle related....i thought i'd access the automotive-world brain power on here for possible answer. even local Chrysler/Toyota dealer gurus couldn't answer it. so here goes.
    in my fleet is a low mileage 2006 Dodge Dakota Club cab with SOHC 4.7 magnum V-8.
    question also applies to my 2007 Toyota Yaris sport coupe.
    both have nearly identical heater and a/c controls. on the control pod area for both is blower motor speed knob...temp adjustment knob....outside/recirculate control knob...and most importantly small button you push IN to activate the a/c system which seems to directly turn compressor on and off. it illuminates when pushed in.
    when i'm driving either vehicle on hot day i set controls as follows: temp knob to max cool...other knob set to recirculate...fan speed knob to high...and push the a/c button IN. result on both is nice icy cold a/c air.
    when the temp gets comfortable i reach over and press the a/c button which turns off the compressor but everything else remains the same. then when it heats up inside again, i push button back IN and cools off.
    PITA on trips, as you can imagine. but doing this does give the compressor a rest.
    here's my question: if i set everything as above...leave a/c button pressed in...then adjust temp knob for nice comfortable cabin temp....does it keep the compressor running constantly? or cycle the compressor ON and OFF? as mentioned, even local dodge and toyota guys don't know.
    THANKS MUCH!
    Compressor gets cycled on and off automatically by a controller. There are pressure sensors on the lines that will tell the compressor when to kick on or not in addition to the temp setting. Often times, the MAX setting is just A/C with the air inlet door set to recirculate. Turning the compressor on and off manually isnt going to help much. Some people do it when they need extra power, but a lot of cars will automatically sense when the the throttle is wide open and will cut out the compressor until the driver lets off the gas.

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    Senior Member 34nineteen's Avatar
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    Quote Originally Posted by Sdrxb12s View Post
    The compressor always runs when you have ac on. Turning the control temp knob on most vehicles will open a damper to allow warm air from outside to mix with the cooled air. But i dont know how all the models work. Some have clutches some dont.

    No... pop the hood and watch your compressor. You will see the clutch engage and disengage without having to turn the switch on and off. A car needs the clutch as you can not just shut off the compressor as you can with home A/C. Just like in home a/c you can not run the compressor continuously. ON A CAR There is a door that will mix warm and cool air to regulate temperature.
    Last edited by 34nineteen; 07-24-2020 at 06:41 PM.

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    There isn't any door that mixes cold and warm air in a home ac unit

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    Senior Member 34nineteen's Avatar
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    Quote Originally Posted by Sdrxb12s View Post
    There isn't any door that mixes cold and warm air in a home ac unit
    Right....

    unless you live in a 2006 Dodge Dakota Club cab with SOHC 4.7 magnum V-8 or a 2007 Toyota Yaris sport coupe.

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    Senior Member BuellyBagger's Avatar
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    34:19 is correct. Most vehicles use a blender door to control the temperature when u adjust the "hot to cold" knob or in some cases a digital temp. On ford vehicles (I've only got fords, so I am most familiar with them) on "max ac" the climate control is on recirculate, full cold, full fan, and the compressor will run as much as it can without over pressurizing the system or freezing the evaporator (both sensor controlled) the compressor in this case actually runs less than it does on just AC on because it is recooling cabin air. So, as to John's question.... the compressor should still be cycling when ac is on. Some vehicles have a variable displacement pump (have no idea which ones just read about it in a class once) they may kick on and off less due to their ability to vary pressure depending on demand. Most efficient way to achieve your desired temp is either what you're doing, which is minimizing the amount of time the compressor runs or use the temp control and allow the vehicle to cycle the system. Modern compressors dont really effect mileage in as much as they used to, so it's kind of a crap shoot.

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    This is an interesting thread. Someone is saying their a/c is to cold. Lol jk. You will be fine with the a/c turned on. Just adjust the temp. That's what I do in my camry, mustang, and Acadia. Now my f 150 I just set to desired temp, i.e. 70 degrees, and let her eat. Or I should say used to. Now I open the sunroof, roll down the windows and open the black glass because my a/c system is shot.

  9. #9
    Senior Member Endopotential's Avatar
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    Where are Click and Clack when you need them? Really miss the Car Talk program.

  10. #10
    Senior Member 34nineteen's Avatar
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    I think one of them died a few years ago? I remember the radio show growing up. For you young ‘uns that was like a podcast.



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