MAX AirCon and MPGs. Yeow! Ouch!

I thought that the actual MAX setting on the AC (where it says MAX instead of a temperature) forced the ICE to stay on constantly.

If you were driving when you turned it from MAX to a lower temp, you may have been in one of those 'in-between' stages where it won't shut off until you stop for 10 seconds or so, or go above 36 MPH and coast to let it shut off.

 

I keep my AC on at all times, set anywhere from 72-76. I still average in the lower 40's, even though my driving style is anything but economical.

Yes, the AC uses more gas, but it shouldn't drop you to 30 mpg...

 

<div class='quotetop'>QUOTE(jimmyhua @ Jul 3 2006, 05:43 AM) [snapback]280461[/snapback]</div>

man thats hot! :huh: :lol:

 

AC must be a killer! We have had brutally hot weather in New York...I had car in Park to set up phone and learn accessories...

AND I was running AC at MAX! Duhh....now I have it set to 80 degrees and let the car do it.

Do you have to manually set the fan to low when on AUTO AC?? or does AUTO change the fan settings as needed just as it does recirculate vs. outside air?

terri

I am going up...will fill up soon ..since I am only going to get around 300 miles on my first tank....live and learn.

I don't chintz on AC with hubby in car...very fragile health and this kind of heat can kill...so I crank it up when he is there....but I still use AUTO, just lower the temp to 72 or 75...

 

We had over 20 straight days last month in LA of 100+ degrees. Highest I saw was 119 in Woodland Hills. My mpg dropped from my usual 49.6 to 49.3. I'm not complaining. I was more comfortable in my car than at work or at home. The .3 mpg is a small price to pay. I do 90% freeway 90 miles a day over two moderate mountain passes.

 

no one should need too much AC... after all, 82 degrees is supposed to be perfectly comfortable for a naked adult male :lol:

 

<div class='quotetop'>QUOTE(subarutoo @ Aug 3 2006, 12:59 PM) [snapback]297210[/snapback]</div>

I'm in the same area, had mine set at 78 auto and it blasted the entire 12 mile drive home and I was averaging 42-43mpg. I have it off now and I'm back up to 45-47mpg.

 

I'm in PA, drive a combination of hills, back roads and highway. I start out with Max Cold and full blast fan, recycling the air, and when the car feels comfortable to me, I turn the fan down to low and raise the temp to about 70. I've been averaging about 52-53 mpg. I thought the recent heat wave would impact this, but so far so good. I did start parking in the shade as much as possible, though, so the car doesn't have to work so hard to get cool. I'm a winter person, though, and I like it cooooold!

Bonnie

 

When it comes to A/C, "auto" mode with the temperature turned up to the point just between comfort and discomfort (ie, it's cool enough, but you can still just barely feel the residual humidity in the air when you breathe) and recirc on (once the initial hot-air load from the vehicle being parked is removed) tends to have the absolute minimum impact on MPG..

Max A/C is the absolute worst thing to do inn terms of energy use- I had an old home A/C unit that didn't have a thermostat, just high/low/fan settings, and the thing just ate electricity; I recently broke down and bought a new unit with a thermostat and variable speed fan- the new one, by the UL-label, should use almost 1.5x the electricity as the old one, but because it has a thermostat and cycles on/off as well as changing fan speeds vs. staying on at max capacity all the time, actually ends up using only about half what the old one did..

 

I need a road-trip to get up to 46MPG lately. It's been that way for more than a month.

I'm hoping cooler weather (low 90's, maybe) will bring back the 46MPG I could get just kicking around.

Unlike some people, my MPGs only venture into the 50's when I leave town...

 

<div class='quotetop'>QUOTE(subarutoo @ Aug 3 2006, 03:59 PM) [snapback]297210[/snapback]</div>

Yeah, but what was the humidity level? This latest heat wave knocked about 4 or 5 mpg off my MPG. Not only was it 100 degrees, but there was very high humidity too. Moisture in the air holds a lot of heat energy, so it takes considerably more energy to cool moist air than it does to cool dry air. And the hotter air is, the more moisture it can hold. That why "relative humidity" is "relative". It's based on the amount of moisture that the air can hold at it's current temperature. There's a lot more moisture in 100 degree air with 90% relative humidity than there is in 80 degree air with 90% relative humidity.

When it's 85 degrees or so, my AC, which I set at 75 degrees, would cut back to almost nothing in 3 to 5 minutes. With the 100 degree humid temperatures we had in the NE this week, my AC would still have the blower running at 70% or so after 35 minutes of driving. And the air coming out of it could only be decribed as cool, not cold.

Humidity plus temperature is the MPG killer. That why the original poster, from Guam, was taking such a hit in 100 degree weather. It's humid in Guam. But those of you in Southern California or the middle of Texas don't have the same humidity and won't take the same MPG hit.

The heat buffering effects of moisture in the air is also the reason why in the desert it may go from 100 degrees during the day to 60 degrees at night, while in humid places like the South East, it will go from 95 degrees during the day to only the mid 80s at night.

 

Two people in the car will dramatically reduce mileage per gallon due to weight. Also two people generate more heat, therefore causing the A/C to run more often and longer.

 

<div class='quotetop'>QUOTE(efusco @ Jul 3 2006, 07:54 AM) [snapback]280464[/snapback]</div>

I had the A/C set to 82 last week when it was in the high 90's here in Chicago, with no clouds and fairly high humidity (more than CA, less than FL, rather like VA or even Dallas when I lived E. of there, which is more humid than many people associate with TX). Anyway, the A/C was running constantly, and my mpg was showing values like Jimmy (OP) described. And the worst was on a 30-minute drive with no stops (other than a few stop lights) with speeds between 30 and 65 mph. It was averagine 30, 35 mpg, with a couple spikes up to the 60's (maybe the compressor turned off for a bit during that stretch?) Luckily my average only dropped from 53 to 52.6, but usually a long drive like that brings the average up. I turn on the recirculation after a couple minutes of driving. When the car is parked at work I leave the windows cracked and a sun shield set up.

 

One thing that will determine how hard your air conditioner has to work is the exterior color of your car. White and silver cars will reflect heat while darker colors like black, etc will absorb it.

We did a test with a laser temperature gun to determine the comfort difference we feel between white clothes and dark colored clothes in direct sunlight. The temperature gun gives accurate surface temperatures.

We had one person wearing a white t-shirt in direct sunlight during a high UV period of the day (12:00 noon) and another person wearing the same brand t-shirt except it was black. It was on a nice day in L.A..

The white t-shirt registered a surface temperature of 82 degrees F. The black t-shirt registered a surface temperature of 141 degrees. To say we were shocked is an understatement. And, no, the guy in the black t-shirt wasn't getting steamed up sitting next to Jennifer Aniston in a cut-off white t-shirt. This was actual surface temperatures with two guys sitting side-by-side in the sun. B)

I am ordering a Prius today, and because I work out of my car here in good ol' So Cal, while I really like the look of the black Prius, I'm going to order silver. My first company car was black, and after sitting in direct sunlight the AC had a hard time keeping up during the summer. The rest have been light colors and seem to be cooler.

RG

 

<div class='quotetop'>QUOTE(Randy G. @ Aug 12 2006, 11:38 AM) [snapback]302185[/snapback]</div>

Mythbusters examined this and confirmed that darker colored cars do get hotter and stay hotter.

The other thing is to TINT your windows for maximum IR rejection that you can get without affecting the GPS and other wireless communication devices. This will also keep your A/C usage low and MPG high.

 

<div class='quotetop'>QUOTE(NuShrike @ Aug 12 2006, 02:59 PM) [snapback]302224[/snapback]</div>

That's good to know. I watch the show from time to time but I never saw that one. My favorite show was the rocket powered Chevy...least favorite was the exploding stomach and the test of different motion sickness remedies. Yuck!