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Old 05-18-2015, 07:25 PM   #15
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Sheesh, I hardly notice a difference in mileage with anything I tow; the dash A/C will make no difference.

Oh, and running the generator has no impact on fuel mileage.....the generator just consumes so much fuel per hour.
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Old 05-18-2015, 07:51 PM   #16
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I'm with those that say you won't see much of any difference in mileage. The wind and speed is going to affect it more than that little compressor. My previous coach had the 275 ISB and I couldn't tell any difference to speak of. I had the ScanGuage and on instant milage saw maybe a tenth or two mile per gallon difference. At first I watched the milage like a hawk. I figured out that it made no difference, it's going to use what it uses and the only thing you can do about it is park it instead of drive it. Don't stress yourself watching gas milage, it will only decrease your enjoyment. When it needs fuel just fill it up and go on whistling.
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Old 05-18-2015, 09:24 PM   #17
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That little compressor is working hard and uses somewhere around 8-10 hp. Say you are using 200 hp to push that big coach through the air and keep the tires turning. So, the a/c adds 10 hp or about 5% to the engine load. If those figures are in your ballpark, figure a 5% drop in fuel economy. Results will vary with the duty cycle of the a/c compressor, road conditions, terrain, engine size, etc. etc.etc. but that should be somewhat close.

Compare to a generator, which typically uses 0.5 gph at 50% load, and 50% of rated watts would run two roof a/c's on most coaches and have plenty left over besides. You only think that genset is wasting fuel cause you can hear it.
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Old 05-18-2015, 09:27 PM   #18
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Actually, it's not so much the compressor, but on side radiator coaches, when the compressor kicks on, the hydraulic fan starts running on high speed. These hydraulic fans can suck up as much as 60 hp. That's why the MPG decreases.
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Old 05-18-2015, 09:33 PM   #19
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Actually, it's not so much the compressor, but on side radiator coaches, when the compressor kicks on, the hydraulic fan starts running on high speed. These hydraulic fans can suck up as much as 60 hp. That's why the MPG decreases.
Yep, biggest draw is the engine fan being on high.
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Old 05-18-2015, 09:40 PM   #20
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5.75 MPG w/o AC. 5.67 with the dash AC
That's pretty low mileage! Our 50,000# Magna towing our Honda Odyssey gets 7.6 according to the VMS and that's with three different drivers over 45,000 miles.
Are you sure your figures are correct?
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Old 05-18-2015, 10:00 PM   #21
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5.75 MPG w/o AC. 5.67 with the dash AC
Yes, that is pretty bad mileage. That's about what mine was getting when I discovered the hydraulic fan was in default causing it to run full blast all the time. After finding a broken wire and fixing it, my MPG rose to about 7.5.
It cost me $800 to fix it, but I recouped that in fuel savings last season.
You might want to check and see if your fan is running full speed all the time.
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Old 05-18-2015, 11:07 PM   #22
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I am often amazed at the things folks worry about.
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Old 05-19-2015, 12:35 AM   #23
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Actually, it's not so much the compressor, but on side radiator coaches, when the compressor kicks on, the hydraulic fan starts running on high speed. These hydraulic fans can suck up as much as 60 hp. That's why the MPG decreases.
Hydraulic fan on our coach has nothing to do with the AC. We have a separate fan and radiator on the opposite side of the engine radiator for the AC. Two small electric fans provide the cooling.
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Old 05-19-2015, 01:31 AM   #24
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"Not enough to ever make me turn it off."
"I am often amazed at the things folks worry about."

Without a doubt, very true statements. If one purchases a D/P motor home and worries about the miniscule cost of running the dash A/C, I'd probably not have purchased the coach, or any coach for that matter. It costs money to be "cool", albeit , again, miniscule. We get 7-8 no matter what so, I'm definitely going to keep cool if and when needed.
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Old 05-19-2015, 02:13 AM   #25
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I've read somewhere that running your in dash air will cost you around 1/2mpg. I run my generator and roof AC unit if it gets so warm that I need to cool down (in the SW now and I definitely need AC). It creates no drag on the engine and will cool you off a sight better as well. In the long run it's more cost effective. JMHO
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Old 05-19-2015, 04:14 AM   #26
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On some automobiles it costs more to roll the windows down than to run the AC. Because of the aerodynamics of the vehicle.
But then a MH is just a box going through the air, not much for aerodynamics...
I run whatever it takes to be comfy... YMWV
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Old 05-19-2015, 07:21 AM   #27
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"Not enough to ever make me turn it off."
"I am often amazed at the things folks worry about."

Without a doubt, very true statements. If one purchases a D/P motor home and worries about the miniscule cost of running the dash A/C, I'd probably not have purchased the coach, or any coach for that matter. It costs money to be "cool", albeit , again, miniscule. We get 7-8 no matter what so, I'm definitely going to keep cool if and when needed.
Scott
Oh! I finally ran across someone on here that thinks like myself, your all going to die of stomach ulcers the way you worry....smh
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Old 05-19-2015, 07:37 AM   #28
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I don't notice any difference with my 42 DP using dash air.
See how it goes.
CampDaven

I too see no measurable difference in MPG with or without the dash air.
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