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01-06-2019, 07:14 PM
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#1
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Senior Member
Ford Super Duty Owner
Join Date: Feb 2017
Location: Manhattan (Little Apple) Kansas
Posts: 2,476
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Running AC with Dash or Generator
I have the coach listed below and it has 380 HP Cummins diesel and also has an Onan 8000 watt diesel generator. I read in the owners manual that I would use less fuel running the generator and house air conditioning rather than running the dash air in the coach. Is that true?
__________________
2020 Newmar Baystar 3005 Gas V10 - 2020 Jeep Rubicon
1280 Watts Solar - Victron MultiPlus-II 12/3000/120-50 120V Inverter
300 Amp Lithium Battery
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01-06-2019, 07:29 PM
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#2
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Senior Member
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I've heard that to be true but seen nothing but opinions.
As for us and our coach, the dash air keeps us comfortable. With all that windshield the roof AC's cannot do that.
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Tim
Leesburg, FL '07 American Tradition 40Z Cummins 400 ISL
Towing a '14 Honda CRV Both sold
2021 Vanleigh Beacon 41LKB 5th wheel
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01-06-2019, 07:51 PM
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#3
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Member
Monaco Owners Club Vintage RV Owners Club
Join Date: Oct 2017
Location: Arizona
Posts: 92
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Quote:
Originally Posted by CWSWine
I have the coach listed below and it has 380 HP Cummins diesel and also has an Onan 8000 watt diesel generator. I read in the owners manual that I would use less fuel running the generator and house air conditioning rather than running the dash air in the coach. Is that true?
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I wouldn't agree with that. The engine AC wouldn't tak that much horsepower from the engine. But, thats a big rig. That dash AC will not cool the whole cabin in the summer. So most people run the generator for the roof ACs while driving anyway.
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01-06-2019, 08:11 PM
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#4
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Senior Member
Join Date: Jan 2018
Location: UT
Posts: 1,244
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Sorry, I don't believe that statement in your owners manual. The AC compressor is only a minor draw on that big diesel engine.
__________________
Ed
2023 Geneva 28VA
Solar and LiFePO4, 2018 Jeep Grand Cherokee Toad
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01-06-2019, 09:04 PM
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#5
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Senior Member
Country Coach Owners Club
Join Date: Jan 2011
Posts: 1,204
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I've talked to a number of Cummins engineers at RMCA rallies over multiple years. It's gospel to them. I choose to believe them. I haven't got the energy, time, or money to investing in trying to disprove them.
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01-06-2019, 09:09 PM
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#6
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Senior Member
Ford Super Duty Owner
Join Date: Feb 2017
Location: Manhattan (Little Apple) Kansas
Posts: 2,476
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Quote:
Originally Posted by iluvuk
Sorry, I don't believe that statement in your owners manual. The AC compressor is only a minor draw on that big diesel engine.
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I included a snapshot of my manual that came with my coach. Look at the second question in the FAQ.
__________________
2020 Newmar Baystar 3005 Gas V10 - 2020 Jeep Rubicon
1280 Watts Solar - Victron MultiPlus-II 12/3000/120-50 120V Inverter
300 Amp Lithium Battery
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01-06-2019, 09:39 PM
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#7
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Senior Member
Monaco Owners Club Ford Super Duty Owner
Join Date: Dec 2008
Location: Kingsville TX
Posts: 1,754
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I didn't buy a RV to save fuel
We had a 04 Monaco DP 38 FT in SoCal or Nevada 110 degree heat we ran the 8k onan AND dash air full bore all the time while traveling, since we have sold it because DW hated the hot bed ( over the engine) at nite,would take3 to 4 hrs to cool down, that's one of the reasons we went with a class c.
Ra. All the time with dash ac on full and genset running 2 13.5 ac units figure 1/2 gal/hr for genset still got 7.8 on a gallon with a 330 ISC note the rear fan draws 15 hp at 1800 ac draws 3hp
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01-06-2019, 11:58 PM
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#8
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Senior Member
Join Date: Jan 2018
Location: UT
Posts: 1,244
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Quote:
Originally Posted by CWSWine
I included a snapshot of my manual that came with my coach. Look at the second question in the FAQ.
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sorry. Didn't mean to imply I didn't believe you. I believed you were telling the truth. I just don't believe the statement means the dash air burns more fuel than running gen set. after reading your manual, I still dont think that is what it is saying. it is simply saying that the gen is an efficient way to run roof ac and that is what it is for. I would never idle my coach at a camp ground in order to run dash ac. that would be inefficient. the gen would be more efficient than that. to me that is what the manual is saying. however, if already driving, use dash ac. it won't affect engine at all, while your at it, run gen and roof ac too if needed. my interpretation.
__________________
Ed
2023 Geneva 28VA
Solar and LiFePO4, 2018 Jeep Grand Cherokee Toad
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01-07-2019, 05:48 AM
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#9
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Senior Member
Join Date: Aug 2016
Posts: 1,817
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Is this really a concern? Even with my 20+ year old Class C traveling on a budget I just fire up the generator or the dash air or both so my chocolate bars don't melt.
Looking at your rig and toads I can't imagine what you're trying to save.
Just use everything as it was intended to be comfortable.
On my Class C there was no noticeable increase in fuel usage using the generator on a 2,000 mile trip.
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01-07-2019, 06:14 AM
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#10
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Senior Member
Join Date: Nov 2005
Posts: 7,383
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...who cares?????, MPG is it not what I bought a 33,000lbs "recreation" vehicle for.....
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Old Scout
2015 IH45 Foretravel
2003 Alpine 40' MDTS [Sold]
New Braunfels, Texas
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01-07-2019, 06:28 AM
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#11
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Senior Member
Join Date: May 2017
Location: Metamora, MI
Posts: 5,518
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I am also a bit skeptical that turning on the A/C compressor while driving will take more adaptive fuel cost than starting and running the generator and roof top air units.
Sure, if you are parked then running the big ole diesel just to run dash air will be fuel inefficient, but their manual specifically says while driving.
But the fuel cost will be what it is. Get comfy and enjoy the ride.
__________________
2002 Newmar Mountain Aire Limited 4370 w/ Spartan K2 and Cummins 500hp
ASE Master Certified (a long.....time ago...)
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01-07-2019, 06:29 AM
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#12
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Senior Member
Join Date: Jun 2017
Posts: 2,807
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Quote:
Originally Posted by CWSWine
I included a snapshot of my manual that came with my coach. Look at the second question in the FAQ.
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That does not say that you will use less fuel running the generator and AC vs the dash AC.
It says the generator uses less fuel than your engine. Of course it does, but the engine is much larger and used to move the coach down the road as well. Will you get better gas mileage on your engine if you run the generator and AC? Yep, even if you're running the dash AC because the generator and AC is taking some of the heat load.
It should also be noted that your house AC is generally rated at less BTUs than your dash AC.
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01-07-2019, 06:41 AM
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#13
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Senior Member
Join Date: Aug 2017
Posts: 2,091
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When traveling there will be little difference in fuel consumption with the dash A/C or the generator running the coach A/C units. A diesel engine will burn .06 gal/hr/hp. So if your engine uses 10 hp for the dash A/C you will burn .6 gallons more per hour. Running the generator will use .6 gallons per hour for the same amount of cooling as your dash A/C. If you are parked , then running the generator will be more economical .
__________________
1993 Tiffin Allegro Bay 32'
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01-07-2019, 07:56 AM
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#14
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Registered User
Join Date: Oct 2016
Posts: 2,078
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Maybe that explains the very high hours on generators in some of the Class A's for sale. there are only a few with very high hours and many with very low hours
If the dash air does the job, why have the generator running? Run it as needed for comfort and as noted don't idle the engine for AC, that is definitely generator duty
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