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Baffling Automotive A/C question-NEVER found an answer

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Barrett

Barrett

Well-known member
Joined
Jun 1, 2020
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963
Location
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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!
 
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.
 
Barrett said:
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!
Click to expand...

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.
 
Sdrxb12s said:
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.
Click to expand...


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.
 
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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.
 
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.
 
I did 15A work (A/C and electrics) for several years at Ford dealers as a young technician and 34:19 is exactly right. Nice description BTW;)

Don't worry about wearing out your A/C compressor John, its a metal to metal clutch with no friction material to wear. Just set the temp to a comfortable level and let it do its job. You are just turning the compressor control circuit on and off, so the compressor will just run longer to get the refrigerant to the right pressure again and pressure switch will still cycle the clutch as necessary. "Max A/C" doesn't make the A/C work harder, it just opens the recirculation door to use the cooler cabin air instead of hot outside air (and on some vehicles also run the fan at max).

A small side note: Compressors really, really, hate to start up with a high head pressure. Some old wives tale went around Phoenix when I worked at Sanderson Ford in the 90's that if you bypassed your A/C compressor pressure switch to make it run 100% it would be colder. Nope. The old York piston style and even the Sanden rotaries would blow up pretty quickly. Lots of warranty denials. Even best-case they would just freeze over the evaporator core into a block of frost... no air flow, no cooley-cooley.

{rant}
I can't STAND it when someone gets into a hot car with "auto climate control" and cranks it to 60 degrees. They think they are setting the temp of the air coming out of the vents or something!?! Set it to the damn temp you really want and leave it the Hell alone! It will run FULL BLAST freezing air to get to that comfortable temp and then stay there automatically. Thats the POINT of "auto climate control"....

Or removing the A/C compressor on a factory A/C '70 El Camino to get that ONE more HP?
Or wiring an electric cooling fan to the ignition or a toggle switch instead of using a temp sensor?
:upset:
{rant off}
I'm such a grumpy old man, hahaha:)
 
CHRIS....CODY....AARON....SHAUGHN....can't thank all of you enough for taking the time to walk me thru this. wasn't fond of posting a puzzling automotive question on here but honest to God....even the local toyota/chrysler service guys i asked, never quite knew which method was proper. your collective brilliance is greatly appreciated, believe me.
 
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Still? I doubt that, unless teenager or 'track car':rolleyes: Re-engineering the accessory drive on anything later than the late 80's with serpentine is a bigger deal than cutting a v-belt. Anyone dumb enough to think removing A/C will help, isn't smart enough to do that, haha. Heck, A/C compressors aren't even heavy anymore.

And youngsters are sissies and need their precious cold air. Sweat like a MAN! LOL.
 
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Sorry, I've never been into 'reality shows' or 'YouTube content' begging for likes. I'm already a mechanic, theres not much I need to know that some media show can teach me.

239850AC-8579-4440-ACFB-0D9543CFD864_1_201_a.jpeg LOL

I'll watch some of the MotorTrend stuff because I know those guys, but purely for the silly/adventure stories.
 
Dont let Cooter fool you. You nailed it with him being a classic car build show junkie.

This is Cooter all day long...





This is more my speed.

 

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