AC and fuel mileage

[red1ton]

Has anyone seen a difference in fuel mileage with the AC on or off? Since this engine has so much HP, I assumed it would not make any difference. My mileage ranges 13. 5 to 15 mpg empty (mostly around town with a little highway) with the air on almost all the time. At 65-70 mph, the computer claims I get an average of 21 mpg.

 

[LSMITH]

If there is a differance in MPG's it is small, like less than 1. 5 MPG. I am running the air all the time these days too and I have not noticed a drop.

 

[Floor It]

I too lose mpg while running the A/C. about 1. 5 mpg in town

 

[HC]

AC does make some difference; how much depends on "in town" or "highway", but I'd say ~1mpg is as good as anybody's guess. I think that in town it makes a bigger difference, 'cause if you're sitting at a red light, the AC is the only thing working, and work = fuel usage. Once you're up to cruising speed, the % of drag caused by the AC is a relatively small percentage of the overall wind drag and other resistances. If you back off the speed just one or two mph, it would probably make up for the AC.

I think the bottom line is, use the AC when you need it, but yes, it does cost something, so turn it off when it is not really needed. In most cases it is worth it!

 

[TowPro]

keep in mind that rolling down the windows with the AC off affects your drag and will also lower your MPG!

 

[illflem]

I've never checked mpgs with AC vs. not, but have installed a intake air temp gauge and have found that with the AC on the temp will climb almost 50°. That's quite a bit when you consider the inlet temp usually runs between 60°-90° depending on the outside temp. I attribute the rise in temp to the fact that the AC condenser is in front of the inner cooler and feeds it hot air when the AC is operating. The diesel engine is most efficient when the intake temp ranges between 50° and 90°, the AC pushes it way beyond this. I don't think the added load of the compressor will effect mileage much.

 

[Cobra]

AC/mpg

I just came from a camping trip in the mountains of Pa. Hauling a 3200# slidein with the AC on full and got 12 mpg. That is compared to my 92 ford empty which got 14 in the mountains. Not too bad huh.

 

[Marco]

I think good part in the MPG loss is due to the fact that the AC condenser heats the intake air quiet a lot.



I've checked that the other day. Temps were in the high 80's outside. With the truck at idle, AC full power, the AC condenser was 125°F!



I've also noticed an smoke increase with the AC on.



Marco

 

[Vaughn MacKenzie]

I noticed on the highway, A/C use doesn't make any noticeable difference. But Marco and illflem hit it on the head. . . I think most MPG loss is due to heated air, not component drag. Cruising down the highway gives you better airflow to help keep intake temps down.



A month ago when we had a week of 95-100F I noticed at least 1. 5mph drop, running around town. Also a considerable loss of power, and MUCH more smoke. When the temp suddenly dropped to the 80s it ran like a racehorse again.



Vaughn

 

[Floor It]

All this sounds logical but my 96" 12v had no mileage change with a/c on or off. In town driving.