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2002 TUNDRA V8 LIMITED 4x2 TRD.

Does using the AC in the highest fan setting make the truck burn up more gasoline than using the AC on the slowest fan setting or it does not make a difference??? anyone know?? Dont post if u got comments about dumb question....
 

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Re: Using AC ON SLOWEST FAN SETTING VS HIGH FAN SETTING?? FUEL ECONOMY SAME???

I am almost 100% sure Mythbusters busted this myth....
 

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Re: Using AC ON SLOWEST FAN SETTING VS HIGH FAN SETTING?? FUEL ECONOMY SAME???

the ac compressor is either on or off so it does not make a difference.

now does the blower motor draw a lot more current on the high setting to put more of a draw on the alternator to affect fuel economy, i would say maybe .01 mpg.

I think the mythbusters did ac on or windows down

Andrew
 

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Re: Using AC ON SLOWEST FAN SETTING VS HIGH FAN SETTING?? FUEL ECONOMY SAME???

I think (as in I do not believe what I see on mythbusters) that this would depend on how many times the compressor cycles during a given period. When on the compressor will eat between 5 and 8 horsepower and thereby affect fuel economy. It is commonly accepted that it is more efficient to use the AC on the highway than it is to run with the windows down as the air resistance with windows down at highway speeds eats more gas than running the AC.

If running the AC on high means the compressor cycles 30 times an hour and running it on low cycles the compressor 10 times an hour then I would expect to see a difference in fuel economy. How much of a difference or if it could even be measured is another thing entirely.

Excellent thought provoking question. Maybe someone with a scanguage could test this and post the results.
 

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Re: Using AC ON SLOWEST FAN SETTING VS HIGH FAN SETTING?? FUEL ECONOMY SAME???

I think the loss of mpg for using the ac is negligible and I'd rather stay cool.
 

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Re: Using AC ON SLOWEST FAN SETTING VS HIGH FAN SETTING?? FUEL ECONOMY SAME???

For a car, below 45 you can keep those windows down since drag is very slight. But when on highways, keep them up since the drag is crazy high on the freeways.

AC setting shouldn't really matter much, since the compressor like what hofkam83 said is either on or off. Just make sure that the engine doesnt idle above 750 RPMs when its on (if it goes over, then you have too much AC fluid and you would idle high and the car would lurch at stops)
 

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Re: Using AC ON SLOWEST FAN SETTING VS HIGH FAN SETTING?? FUEL ECONOMY SAME???

AC setting shouldn't really matter much, since the compressor like what hofkam83 said is either on or off.
I have to disagree. The compressor is either on or off but it is not on all the time. I can hear mine engage and disengage. I would think that if it ran nonstop it would burn out.
 

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Re: Using AC ON SLOWEST FAN SETTING VS HIGH FAN SETTING?? FUEL ECONOMY SAME???

I have to disagree. The compressor is either on or off but it is not on all the time. I can hear mine engage and disengage. I would think that if it ran nonstop it would burn out.
Agreed. Much like the element in an oven. Maybe what they meant, however, was that there is no low engagement of the compressor.
I wouldnt think fan speed has much to do with fuel economy. Once the cabin reaches the desired temp, the compressor will not come on as much. This would also depend on the outside temp and things like window tint or where the sun is at the time. If the sun is not beating inside the cabin, or there is tint to cut the heat, the cabin should stay cooler. Hotter temps in the cabin means the compressor stays on longer or cycles more to hold desired temp. I would think this would be when the ac would start to eat away at your mileage.
 

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Re: Using AC ON SLOWEST FAN SETTING VS HIGH FAN SETTING?? FUEL ECONOMY SAME???

I have to disagree. The compressor is either on or off but it is not on all the time. I can hear mine engage and disengage. I would think that if it ran nonstop it would burn out.
at idle its a different story it does kick on and off, going down the road it is on the entire time you have the ac on, otherwise you will have cold air then hot air and etc. if your ac is turning on and off going down the road you may need to recharge your system.

Andrew
 

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Re: Using AC ON SLOWEST FAN SETTING VS HIGH FAN SETTING?? FUEL ECONOMY SAME???

Very good question computer tech.

I think my fuel economy would decrease when I have the AC on full blast. Recently I've been running the AC on 1. I I haven't really tested it but I would think using a Scan Gauge would help us member out. But other factors play into this such as temperature, window tint which I have on the truck, driving habits, etc.

Chris
 

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Re: Using AC ON SLOWEST FAN SETTING VS HIGH FAN SETTING?? FUEL ECONOMY SAME???

The low pressure moved up into Canada and a high moved in and brought a heat wave.
Finally, in The Bay Area, California is seriously into summer with temperatures in three digits. As I write this, it is 80 degrees...at 11:30 PM.


Outside: hot


At the vent: cold


Inside: Comfy


And Clyde the ride doesn't even notice


Ahem.....
Just keep comfortable!
 

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Re: Using AC ON SLOWEST FAN SETTING VS HIGH FAN SETTING?? FUEL ECONOMY SAME???

at idle its a different story it does kick on and off, going down the road it is on the entire time you have the ac on, otherwise you will have cold air then hot air and etc. if your ac is turning on and off going down the road you may need to recharge your system.

Andrew
I could be wrong here since I am not an ac expert but this does not make sense. If the compressor ran all the time then wouldnt the inside of our truck be ice cold all the time? It should be no different than your house. You set the temp you want, the ac works till it hits desired temp, then shuts off. To hold that temp it turns on and off. When the compressor shuts off, air still passes over the coil, cooling it off as it does. If its really hot outside, it will have to cycle on more often and stay on for longer periods to hold the temp. Same principal as the element in your oven I would think
 

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our trucks uses air coming from outside or cabin depending on if you have the recirculate switch press, then the air gets cooled by the air conditioner and the passes over the heater coil then to the vents. by moving the temperature dial you vary the heater coil in how much the air is going to get heated. if you have the truck all the way cold you don't feel the ac cycling it just blows cold all the time. the truck just uses a combination of the heater coil, the ac, and cabin or outside air to control the temp.

Andrew
 

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Another question: I have a 2006 Tundra DC. With the temp knob maxed out and recurculation on, and vents on dash / floor it blows good air BUT when I turn the temp down because it is cold in truck, it seems to reroute the air flow. Making the amount of air coming out of vents a lot less. On my wife's 2009 corolla when I do the same thing it just turns down the temp like it is cycling the compresser more. Does this sound right for my tundra?
 

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Another question: I have a 2006 Tundra DC. With the temp knob maxed out and recurculation on, and vents on dash / floor it blows good air BUT when I turn the temp down because it is cold in truck, it seems to reroute the air flow. Making the amount of air coming out of vents a lot less. On my wife's 2009 corolla when I do the same thing it just turns down the temp like it is cycling the compresser more. Does this sound right for my tundra?
yep its normal, i think is happening is when you have the knob all the way closed the air bypasses the heater coil making a more direct route to the vents, but when you move the temp knob up a little it opens up to the heater coil allowing you to control the temp of the air. you can feel it the knob that you are activating something else.

Andrew
 

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at idle its a different story it does kick on and off, going down the road it is on the entire time you have the ac on, otherwise you will have cold air then hot air and etc. if your ac is turning on and off going down the road you may need to recharge your system.
I'm pretty sure the A/C compressor cycles going down the highway. If you put a thermometer in the vent, you can watch the duct temp fluctuate a few degrees as it cycles on and off. The A/C system is controlled by psi, not road speed.

yep its normal, i think is happening is when you have the knob all the way closed the air bypasses the heater coil making a more direct route to the vents, but when you move the temp knob up a little it opens up to the heater coil allowing you to control the temp of the air. you can feel it the knob that you are activating something else.
Moving the temp knob opens or closes the heater valve, controlling how much coolant flows through the heater core. Open = heat. Closed = no heat.
 

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The laws of physics can be bent but certainly not broken.

Think about it: To cool the cabin of the truck from 120 F down to 75 F you have to perform a certain amount of "work". Your air conditioner is doing that as the belt takes away energy from the engine. The cooler the cabin is, the more energy you use.

Therefore, the more energy you use, the more gas you burn !

The Scanguage clearly shows the HP jump up when the A/C compressor comes on. Also, the gallon per hour and Instant MPG. The more cooling you want, the longer the compressor is on, thus the more gas you burn.

As the truck uses a lot of gas already, adding the A/C does not make a huge difference but at the end of the day, A/C is not free.....
 

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I'm pretty sure the A/C compressor cycles going down the highway. If you put a thermometer in the vent, you can watch the duct temp fluctuate a few degrees as it cycles on and off. The A/C system is controlled by psi, not road speed.
I never said road speed just moving vs idle.

Did that today on a 65 mile trip on the interstate. The temp stayed between 38 F and 41 F and seem to vary on the load of the engine like when going up a hill the temp would drop a bit and then going back down would increase. On the extreme i decided to go from about 60 mph to 95 mph wot and see what would happen, the temp dropped to 34 f all the way up to 95 mph and then when i let off it went to 44 f but then went back to the 38 f to 41 f degree range. I used a fluke with the temp probe and stuck the probe just inside the vent. I had the cruise set at 75 mph with the recirculate on and it was about 91 f outside today.





I also had about 20 miles at 55 mph and that temp was rock solid at 35 f.

On the scanguage when you click off the ac manually there is a 35 hp drop but you never see that change while driving except will going up and down hills. Then when you do manually turn off the AC the temp immediately begins to climb and i would say within about 8 to 10 seconds it is back up 60 f





So where is the cycling? you say that vary in 3 degrees is the compressor turning on and off for second or two then turning back on. i would think that would cause more damage than just staying on the entire time but then at 55 mph the temp barely changes a degree.

I took a ton pics of the scanguage and fluke over the entire time i was driving and i need to organize them and probably make some slide show videos to upload instead of uploading them all. i will try to get them up either today or tomorrow.

Then the high speed pic, i would have gone faster but i had some traffic coming up quite and had to shut it down. My speedo is off 5 mph at 70 so at 90 i think i was doing about 97 to 98 mph. Then showing that my truck has 500 some hp, maybe not.





Andrew
 

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Interesting test. Screwy speed. But....now you know.

Does the compressor cycle on/off?

Open the hood. Open the windows. Turn the A/C on to any setting you like. Start the engine.
Go to the front and look and listen.
 
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