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Old 05-26-2005, 09:03 AM   #1
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Which AC while driving?

Camper World had an article on saving fuel in which they suggested that in a MH we turn off the dash AC and turn on the generator and run the roof AC- quote-

<LI>Avoid using the dash air conditioner. If you travel in a motor home, it is more fuel efficient to run the generator and use the roof-mounted air conditioner. The average generator will use approximately one gallon of fuel per hour.

We are still melting the last of our snow but soon it will be spring then our three days of summer and I will want to use my AC. What do you think?
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Old 05-26-2005, 09:56 AM   #2
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Back of the napkin math on this (that's a wide open invitation to proof my math please) would be:

Assuming a gasser like mine getting 7 mpg at 60 mph we would consume 8.6 gallons of gasoline in one hour of 60 mph driving. Adding 1 hour of generator time would consume 1 additional gallon of gasoline

My mileage would drop from 7 mpg to 6.26 mpg using the generator (an 11% drop im mileage). My dash air is broken so I don't know what the effect of dash AC would have a mileage but having more than an 11% effect on mileage seems excessive to me. (someone who knows please chime in on this one).

It's more interesting with a diesel. Assuming 11 mpg baseline. You would consume 5.45 gallons in one hour of 60 mph driving. The generator would consume an additional 1.0 gallon per hour so now you would be getting 9.3 mpg (a 16% drop in mileage)

So the diesel takes a larger "hit" in mileage but thats only because its more efficient to begin with. Factor in Fuel cost differences or an LP powered genset and everything gets to complicated to fit on my napkin.

I think the bigger issue has more to do with the volume of space we need to cool. We're headed to Florida tomorrow afternoon. Even if the dash air worked I don't thin our kids would be comfortable without at least the forward AC running. To really cool the coach while underway in hot weather we really need to run both roof airs.

So, my recommendation would be to just wear shorts and a tee shirt, travel at night and don't run any air at all. Oh, and make sure wherever you go it's downhill from here!
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Old 05-26-2005, 10:30 AM   #3
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I sell RV's for a living and I always tell my customers to just use the one that makes more sense for how you are using it. If one of you is driving, and the other is in the back taking a nap or fixing lunch or whatever, it makes more sense to have the roof air on. If you are both riding up front however, the dash air shoud be sufficient. I have a hard time believing that putting a little bit more force on an already highly-taxed engine is less fuel efficient than running two engines. If it is more economical to run the generator, the savings are going to be very marginal.
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Old 05-26-2005, 11:21 AM   #4
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I drive a 78 28' Argosy, I was also told that it was more fuel efficient to run the roof air. I live in Florida so AC IS A NECCESITY. The roof AC cools the interior very well, however, I put a small occillating fan on the dash to circulate air around me when I'm driving. I have noticed a small loss of power with the dash AC when I'm towing my motorcycle trailer. mileage wise I'm getting about 9 to 11 mph driving at 60-65 with a 454 when running roof ac.
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Old 05-26-2005, 11:27 AM   #5
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Hey Steve, where in Florida are you headed. I like your nose art.

Ray
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Old 05-26-2005, 11:46 AM   #6
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Ray,
We're headed to Jupiter Island; Hobe Sound. Thanks on the noseart - Unforetunately it's only a "mock up" on my avatar of what we plan for nose of our 345.
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Old 05-26-2005, 12:36 PM   #7
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We all know that motorhomes are not fuel efficient on gasoline.

Therefore if we question the relative mileage when using the dash air as opposed to the roof air, should we even be in the motor home in the first place?

Most owners purchase a particulat motor home to satisy their particular wants, needs and comforts.

Granted, the cost of gasoline is ridiculous, but on the other hand what real difference does it make which air is used, when the cost savings is negligible
to the investment in the motorhome?

Relax, enjoy, you worked hard to get it, run both AC's if that's what you want.

On the other hand, if the savings of a couple of cents per mile is that important, then why use the motorhome at all?

Then we could also ask, "why is gasoline cheaper in Hawaii, than it is at home"?

The vast majority of motorhomes owners, worked very hard for many years, to justify the expense of a motorhome, then for gosh sakes, ENJOY IT!


Reduce the kids inheritance.

Andy
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Old 05-26-2005, 12:50 PM   #8
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Excellent point.
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Old 05-26-2005, 01:14 PM   #9
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Sorry Andy, you are way off the mark on this one. The idea is to be able to continue to enjoy the investment. Fuel costs are not likely to come down in fact they will proably go even higher.
I am grateful to Camper World and people like them who take the time to put out beneficial articles that are helpful to us RVers. They are in the busisness to stay in busisness and know how to service thier customers.
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Old 05-26-2005, 02:58 PM   #10
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Steve, enjoy your trip and be safe. I may head to Cedar Key this weekend with the wife and dogs. As for the nose art I think its cool. I've been wanting to do something similar but the wife has objections.
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Old 05-26-2005, 03:55 PM   #11
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Quote:
Originally Posted by Chaplain Kent
Sorry Andy, you are way off the mark on this one. The idea is to be able to continue to enjoy the investment. Fuel costs are not likely to come down in fact they will proably go even higher.
I am grateful to Camper World and people like them who take the time to put out beneficial articles that are helpful to us RVers. They are in the busisness to stay in busisness and know how to service thier customers.
I don't think Andy was blasphemizing fuel economy as a whole...I think he was saying that choosing between roof or dash air by reason of fuel economy is being "knit picky" and I'm inclined to totally agree with him. If someone is using their dash air and sacrificing that much luxury for that small of a difference in fuel economy, then they really do have no business driving a motorhome. As I said before, If dash air is more efficient, and both are riding up front...no reason to spend the extra money. But to have everyone in the back sweating like two rats $#%# in a wool sock simply because you want to save a nickel here and there is ludicrous.

I'll quote the very first line of the Wally Byam Creed... "To place the great wide world at your doorstep for you who yearn to travel with all the comforts of home" The comforts of my home don't include dash air.
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Old 05-26-2005, 04:34 PM   #12
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Don't forget us motorhomers live to calculate our fuel mileage improvements no matter how slight. That IS part of the joy of MoHo ownership! But maybe I'm just a MoHo Nerd.
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Old 05-26-2005, 05:12 PM   #13
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I wonder if they calculated any $$ amount for wear and tear on the generator when running it 8-10 ours a day. They ain't cheap to maintain.

John
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Old 05-26-2005, 08:54 PM   #14
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Most of us are not used to checking the generator oil (speaking for myself) as often as the main engine but if you do run the generator for AC don't forget to check the genset oil every day of driving.

Garry
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