PDA

View Full Version : A/C and Gas Milage


ColePyck
06-14-2007, 07:51 PM
Two things. Do you really get better gas miliage with the A/C off? and I always tell my guys to turn off the AC before you shut off the truck so the compressor wont have hard starts and stops, they never do. So today I pulled the AC Relay Fuse.......I told them not sure what happened but I will get around to fixing it!

David Hartzog
06-14-2007, 08:20 PM
my wife insists this is a myth and that rolling the windows down creates resistance. i think shes a wimp and just wants the a/c on.

i dont have the same problem in my truck right now cause my a/c is out and its an oven in there!

DBL
06-14-2007, 08:23 PM
my grass crew says they only run the a/c from the last lawn back to the shop but i think they run it all day...i cant be there all the time to watch and im not pulling the fuse so i guess theyre running it

fiveoboy01
06-14-2007, 08:33 PM
A/C does indeed reduce fuel mileage. The compressor is a parasitic load on the engine. Energy has to turn the compressor somehow.

Turning the A/C on or off before or after stopping the truck will have no effect on compressor operation.

Supper Grassy
06-14-2007, 08:39 PM
If i recall correctly Mythbusters tried this and it SURPRISINGLY turned out that a/c on is better gas milage

Albemarle Lawn
06-14-2007, 08:47 PM
The engine is warm and the cab is cool.

Want them to enjoy their jobs. Not worried about the gas, they make more every day.


The only reason to turn A/C off first is to prevent fungus and odors from the A/C...turn off the A/C but let the vents blow to warm the evaporator so is doesn't sweat as much for hours after the truck is parked.

cat2
06-14-2007, 08:55 PM
If i recall correctly Mythbusters tried this and it SURPRISINGLY turned out that a/c on is better gas milage



No. I seen that one and the one with the a/c turned off is better on gas. The one with a/c off did 30 more laps.

Petr51488
06-14-2007, 08:59 PM
If you're doing highway speeds then the a.c is better then having the windows down. If you're doing city driving, having the a/c kills the mileage like you wouldn't believe. Especially when you have a loaded trailer with grass in the back of the truck. Sometimes its all worth it when its 100 degrees outside.

Midwest Lawn Services
06-14-2007, 09:05 PM
No. I seen that one and the one with the a/c turned off is better on gas. The one with a/c off did 30 more laps.

That sounds much more logical.

zz4guy
06-14-2007, 09:05 PM
Just my opinion, but don't you think it's worth the extra $2/day or whatever to keep your employees happy? It sucks out there in the summer time!!

lawnmaniac883
06-14-2007, 09:23 PM
I never use the ac when I am mowing solo. Waste of gas, half the time you are just starting to cool off when its time for the next lawn. Slows you down too much IMO. Windows down under 55 is good for me, above that and windows up ac on. I dont think its really good on your body to go from hot to cold hot to cold 15 times a day. If you have a tight route then there is no point in touching your ac all day long.

abcfamily
06-14-2007, 09:56 PM
Just my opinion, but don't you think it's worth the extra $2/day or whatever to keep your employees happy? It sucks out there in the summer time!!

No. I seen that one and the one with the a/c turned off is better on gas. The one with a/c off did 30 more laps.

I fully agree with both the above! :usflag:

fiveoboy01
06-14-2007, 10:26 PM
I left my truck running between jobs today, A/C full blast:)

milsaps118
06-14-2007, 10:33 PM
I left my truck running between jobs today, A/C full blast:)

I'm with you there fiveoboy, I left the truck running with the air full blast, on our last 2 jobs of the day.

Rons Rightway Lawncare
06-14-2007, 10:59 PM
It takes somewhere on the order of 5 horsepower or so to run the A/C on a car or truck. 5 horsepower on a 300 horsepower truck engine is not a big deal and as such your MPG will not be much different A/C on or off.... 5 horsepower on a 110 horsepower economy car engine will be a big deal and will show up as a fair drop in MPG.

In the summertime my A/C is on full blast all day long, even if the drive from one yard to the next is only 2 or 3 minutes long. Any cooling I can get is helpful to get me through a hot humid day.

fiveoboy01
06-14-2007, 11:37 PM
Ain't that the truth. My bud's Saturn with the 4-cylinder engine has a very noticeable loss of power with the AC on...

screensnot
06-14-2007, 11:42 PM
It takes somewhere on the order of 5 horsepower or so to run the A/C on a car or truck. 5 horsepower on a 300 horsepower truck engine is not a big deal and as such your MPG will not be much different A/C on or off.... 5 horsepower on a 110 horsepower economy car engine will be a big deal and will show up as a fair drop in MPG.

In the summertime my A/C is on full blast all day long, even if the drive from one yard to the next is only 2 or 3 minutes long. Any cooling I can get is helpful to get me through a hot humid day.

5hp might be a slight overestimation but otherwise I agree with you.

The V-10 barely notices when the compressor kicks on, but the engine in a Honda really feels the extra work it's doing.

fiveoboy01
06-15-2007, 12:25 AM
I don't think it's an over-estimation. No concrete evidence, but when putting on a smaller crank pulley and larger water pump/alternator pully a 5-10 hp gain is not uncommon.

I think that on my bud's saturn, there's more than a 5hp loss with the AC on because it's REAL noticeable.

SiteSolutions
06-15-2007, 02:18 AM
gasoline contains about 125000 btu/gal
5 hp = about 212 btu/min
typical efficiency of 4 cycle gasoline engine is about 25% (most of the energy goes out the tail pipe or into the radiator)

25% x 125000 btu/gal = 31250 btu/gal
31250 btu/gal / 212 btu/min = about 150 min/gal

So, theoretically, you could run the A/C for 2.5 hours on one gallon of gas, or, A/C takes up about .4 gallons per hour, about $1.25 per hour.

Deisel engines are more efficient and there is more energy in a gallon of deisel, so you might get better numbers on a deisel.

Of course this is a pretty rough estimate...

lawnboy dan
06-15-2007, 07:47 AM
i get such lousey mpg towing the trailer running the ac isnt going to make much diff

stroker51
06-15-2007, 10:09 AM
I didn't know how much of a differnce having my a/c on low made until the throw-out bearing went out in my Powerstroke on wednesday, and I've been mowing in my 84 F250, no a/c, no vents in the dash. It freakin sucks, I don't know how i mowed in that truck for the 2 years before I got my 'stroke.