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Old 05-18-2015, 04:23 PM   #1
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DP owners: does dash A/C use effect fuel mileage?

Maiden voyage this weekend in our American Tradition 40VS, powered by a 300hp Cummins C8.3.

Our previous coach was a gasser (F53 chassis) and when using the dash A/C, mileage would decrease by about 15% or more, plus the loss of power was noticeable. It was actually more economical to run the generator with roof A/Cs on high and leave the dash air off.

So, should I expect a decrease in mileage with the new coach when running the dash A/C, or is the engine powerful enough that it won't make a difference? Your thoughts are appreciated!
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Old 05-18-2015, 04:25 PM   #2
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We have definitely seen a decrease in fuel mileage and found the use of the generator to run the house AC units was a much more effective and efficient manner to cool the coach.


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Old 05-18-2015, 04:29 PM   #3
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Not enough to ever make me turn it off.
Generator is about .6 gal/hour. If it's too warm for the dash unit, the roof air is my ticket.
It just doesn't matter to me.
MH is point to point. Toad is 2/3 of my miles at good mileage.
Drive cool, my friend
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Old 05-18-2015, 04:38 PM   #4
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I run my generator and the roof ACs. Of course there's a mileage hit, but I want it to be comfortable inside. Plus, your generator wants to be run and it likes to run under load.
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Old 05-18-2015, 04:53 PM   #5
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DP owners: does dash A/C use effect fuel mileage?

Thanks for the info, folks. The dash air in this coach works almost too well. It totally cools the front half of the coach. But, when driving 250 miles, a 15% decrease in fuel economy equates to roughly 4 gallons of diesel, or $10. 6/10 gallon per hour for generator usage is only 3 gallons on a 5 hour trip.

Assuming 15% fuel economy decrease from dash air use, generator is less expensive.
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Old 05-18-2015, 05:02 PM   #6
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Really, it uses that much fuel for that big motor to turn that little rotary compressor
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Old 05-18-2015, 05:22 PM   #7
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I don't notice any difference with my 42 DP using dash air.
See how it goes.
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Old 05-18-2015, 05:55 PM   #8
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On any motor vehicle, Gas/Diesel/Other running the dash A/C will affect MPG.

I am far less than convinced that using the Generator and roof air will be more efficient..... HOWEVR

The ROOF air is deisgned to cool the WHOLE HOUSE (Usually this includes the cockpit area) where as the dash air is not.. It is designed for a volume and sun load roughly equal to a semi tractor at best.
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Old 05-18-2015, 06:16 PM   #9
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No difference that I can discern. In any case, our comfort is worth far more than the few pennies per mile it might cost.
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Old 05-18-2015, 06:58 PM   #10
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5.75 MPG w/o AC. 5.67 with the dash AC
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Old 05-18-2015, 07:14 PM   #11
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Quote:
Originally Posted by Scottybdivin View Post
5.75 MPG w/o AC. 5.67 with the dash AC

Towing your F150? Your rig is a lot heavier than mine as well, even without a toad.
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Old 05-18-2015, 07:15 PM   #12
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It has to make some difference in fuel milage but I don't think you can tell in performance. You will probably find out on hot days the dash and house airs need to run.
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Old 05-18-2015, 07:21 PM   #13
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The extra fuel to run the dash AC is not enough to be concerned about, and nowhere near 15%. We run the dash AC and the over-the-road AC in the bedroom if it is not too hot. As temperatures go up, we switch over to generator and roof ACs. And if we are heading into the sun when it's real hot, I may still run the dash AC. Wind has a lot more impact on mileage than running the AC.
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Old 05-18-2015, 07:23 PM   #14
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Quote:
Originally Posted by CampDaven View Post
Not enough to ever make me turn it off.
Generator is about .6 gal/hour. If it's too warm for the dash unit, the roof air is my ticket.
It just doesn't matter to me.
MH is point to point. Toad is 2/3 of my miles at good mileage.
Surely you meant 6 litres or quarts per hour. With a good load in cold weather (20F) I have determined my 8 kw Onan uses just under 1 USgal/hr. (Two ceramic heaters, Aquahot electric and engine block heater). As I recall manual refers to consumption varying between 2 to 5 litres per hour.

Interesting to compare the cost of a cold weather 12 hour Walmart stop with fuel @ $3.50 per gallon versus the cost of a modest RV park with 50 amp service and WIFI.

Up to 100F we have found dash air adequate and no noticeable change in fuel economy as other factors such as speed, terrain and wind direction seem more significant. (05 Monaco Dynasty)
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