Question about Air Conditioning and MPG

[Jay]

The real tangible benefit recirculate has is to remove humidity from the air. Humidity offsets the effectiveness of sweating/cooling down. This has a huge benefit when you have a car full of sweaty people.

If it's 95* outside and 80% humidity, on regular AC that humidity gets pulled into the car with a little removed by the condenser as it's cooled. On recirculate, the same air in the car is recycled numerous times, removing a little more humidity each time until it gets very dry to where you need to blink your eyes more often (but you'll feel cooler due to your own sweat evaporating much faster in the drier air).

But, in terms of mpg, there is no real effect on regular vs recirculate. The discharge pressures from the AC compressor will not change enough to make a large difference in the power required to turn it.

 

[adrianb]

I have been tinkering with different things trying to eek out every mpg i can. I drove with AC off for a couple days and watched my average MPG, there was zero impact. That said, it hasn't been hot here by any stretch so the AC might not be in use very much.

I drive the same route every day so I feel pretty good about my test.

One thing I will say: I also removed my roof rack's crossbars and definitely am seeing a slight mpg improvement - maybe 1 mpg.

Run your own test. Drive with AC on, reset your average mpg number. Turn the AC off, reset the mpg value and see if you notice a difference. Definitely report back.

 

[Jay]

I prefer calculating by hand . Reset the trip meter each time you fill up and use the fill gallons and total miles driven at each fill up. Most accurate over the long run. Also make note of any errant events (longer idle times, more traffic congestion than normal, etc) over the course of each fill.

The best way to increase mpg would be to lower the truck as much as possible, run shorter and narrower tires with light wheels (like a 27 or 28" tire versus ~31" factory tires... yes it will look funny on these large trucks), and install taller axle gears to make up for the shorter tire and further lower highway rpm cruising. Obviously, driving slower helps if that's an option. Target for ~1500rpm at 65 in your tire/gear calculations.

Beyond that and you're looking at engine swaps. I'd be curious to see what a tahoe or yukon would get with the Mercedes 3.0L V6 diesel and GM's own 6L80E six speed auto (GM should offer a package like this IMO). My guess would be another 5 mpg or so over a 5.3.

 

[waxworkz]

Some of the stuff you guys are suggesting, engine swaps, tranny swaps are not worth the investment vs moneys used to run ac. If you think about cost of an engine swap, unless your engine is blown, it would make more sense to drive with the ac on all the time! I have spent about $600 on tune, efans, install time and I only netted about 2 mpg increase. Sure the ac, power and the like are cool, but was it really worth the money spent vs the end result?

Point is, if you don't have the money to fuel the truck/suv maybe selling it and buying a smaller car would be the best option? I tow 2-3 times a week and can not do that with a small car. So for me the money spent on fuel is worth it because I am making money. If it's hot, I run the ac, gas mileage is not as important to me as being hot and uncomfortable. Especially after having worked a few hours in the sun.

 

[04SS99Denali]

if your THAT concerned about MPG you shouldn't be driving a truck of this size with a v8

 

[WHITEOUT]

they did a similar test on mythbusters about driving on the highway while running ac and driving on the hgwy no ac with windows down.it averaged out to be pretty close to the same mpg either way.

I saw episode also and in "real world" actual driving, it was a pretty big difference actually. They got like 40 extra miles or something like that. Ya on a computer test they did, a/c on actually got better mpg then windows down no a/c. ???? Real world driving with a/c on windows up you will loose mpg compared to no a/c on. I personally loose about 2 or more mgp in the summer. Livin in AZ you gotta use a/c! But I personally try to roll down windows n turn off a/c whenever possible to save some gas.

 

[sumo]

Run the dang thing. Kinda hurts the ears driving over 50 mph on the highway, all windows down. Myth Busters Did a segment on this. At highway speeds you are best off closing the windows and sunroof, because opening them often causes enough drag to offset any savings from turning off the air conditioner. When driving slowly around town, where drag is less of a factor, keeping windows and sunroofs open typically uses less fuel than running the AC.
Of course, the most efficient car is one with the AC off and the windows and sunroof closed. Using the car’s vents might circulate enough air to keep you comfortable on days when the weather isn’t particularly hot or when the car’s interior hasn’t been preheated by sitting in the sun.

 

[Jay]

Some of the stuff you guys are suggesting, engine swaps, tranny swaps are not worth the investment vs moneys used to run ac.

We know. You were supposed to snicker and ponder.

 

[WhoDatPanic]

well thanks for all the responses, i guess i will do some own tests too how much do efans cost and what is the benefit?

 

[04SS99Denali]

e-fans can pull more air when your truck is moving slow like in traffic or slow city driving to keep it cool. also you wont have the drag from the clutch fan anymore. you can find a kit from anywhere to 2-500$ from i learned its better to spend the extra cash and get the right shit the first time