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Old 09-15-2009, 02:49 PM   #1
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air conditioning cost comparison

Howdy folks,

Just wondering if anyone out there has done any cost comparisons (fuel consumption) of using dash air conditioning vs. running on-board generator and coach air conditioner(s) while motoring down the highway?

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Old 09-15-2009, 03:25 PM   #2
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The responses that you get will be interesting as I've always been of the impression that you will see a 10-12% reduction is mpg when using the dash air coupled with some power loss. I will occasionally use our dash air only to keep the freon circulated and the seals lubricated. The majority of the time if ac is needed, the gennie running and one or both ac's are going. Makes for a more comfortable coach and excercises the gennie at the same time.

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Old 09-15-2009, 06:35 PM   #3
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Articles written on this subject say that the dash air uses less fuel than the generator.
Jim Walker
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Old 09-15-2009, 07:45 PM   #4
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My experience is on the highways/interstate the genny & roof air is cheaper, in town the dash air. My MH requires both whenever outdoor temps & the orientation of the sun converge on the windshield area. I don't care. I'm not rich but I will be comfortable while having fun & use all as needed.
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Old 09-15-2009, 07:56 PM   #5
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I haven't seen the articles that J. Walker is referring to, but traditional RV wisdom is just the opposite. Even if it is a break even, the roof air is providing a lot more cooling for the same money.

My diesel Onan 7500 only uses 0.3 gal/hour to provide a continuous 20A, which is enough to run one a/c and the fridge as well at a 100% duty cycle. If the a/c ever cycles off, the economy gets even better. The dash a/c always runs full out (even with the temp control set above Max Cool) and it draws about 15 hp from the main engine.

The last time I made a serious attempt to compare was with my1996 gasser and a 460 Ford vs a Onan 5000. The dash a/c cost me a bit under 1 mpg (a 14% decrease) while that Onan used about 0.4 gal/hour to run one a/c and keep the front of the coach cool.

We can't keep the front cool with just the dash a/c unless the temps are below 80, so we use the house a/c anyway.
Gary Brinck
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Old 09-16-2009, 04:04 PM   #6
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I run the generator so I can run both roof ACs and the refrigerator. We set the temp on the back AC two to four degrees cooler while traveling so we do not have so much noise up front. We do the opposite when we sleep. I figure that I have the generator and might as well use it.
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Old 09-16-2009, 06:27 PM   #7
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Me I run the dash air on max about 90% of the time... I almost always run the roof airs when I am 10 to 20 miles away from my next stop. This lets the coach cool before we park. I shut the A/C's off before I plug into shore power. This allows them to reset. My 7k Onan runs both 15k A/C's and the fridge and never misses a beat.

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