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Old 08-06-2015, 10:46 PM   #11
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I don't have a MH but have as much invested if not more. My diesel engine doesn't feel the a/c and I'll run the Onan in the 5er to keep it cool for my little woman if not traveling far. As much money as I have rolling down the road and getting 9 mpg in truck and Onan uses 3/4 gal/hr is little price I pay to have her say ; sure feels good in here babe. Puts a smile on my face. LOL if we are going 6 hrs away I'll stop an hour before we get there and turn on the Onan so it nice for her. LOL She's spoiled!!!! My fault.
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Old 08-07-2015, 11:46 AM   #12
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Living here in FL, we run both the coach and the cab a/c almost all the time. I keep the unit plugged in with the air on in the driveway and I want it cool when I park for the night - not an hour or two later. On the road, I set the cruise at 63 mph and that brings us to 1700 rpm - ideal cruising with the DP. As for what fuel the generator uses, don't you just hate it when you check into a nice hotel and they've had the air off all day so it takes three hours for the room to cool down? Me, too!
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Old 08-07-2015, 05:15 PM   #13
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The number for the coach A/C sounds low, I would say they should be about the same, the chassis maybe even a little higher.

I'm guessing the chassis A/C is around 20,000 BTU, This will require about 7hp. If we use a fuel burn of .5 lbs per hp, thats about 3.5 lbs per hour. Gas is about 8 lbs per gallon so it would be just under 1/2 gallon per hour to run the dash A/C
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Old 08-07-2015, 09:46 PM   #14
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Read my post of last year that the originator of this thread referenced. Its title is: Running coach A/C vs cab A/C while driving.

Efficiency is closer to 0.4 pounds of gas per horsepower hour. The cab A/C does not have to run 100% of the time to keep it cool. Gasoline weighs 6 pounds per gallon.

The two or three horsepower required to run the cab A/C is a small percentage of the 125 hp more or less that the engine is developing at cruise. Even if you ran at full throttle you probably wouldn't notice the difference with the A/C on or off. The differences in engine cooling load, fuel consumption and engine wear are insignificant.

In short, if the cab A/C keeps you cool, just use only it. Use the generator and coach A/C if you need it.
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Old 08-08-2015, 01:12 AM   #15
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In theory, it seems simple that the cab a/c is more efficient. I just don't think revving the engine is a valid test when comparing. You can easily feel the lag when accelerating when the cab a/c is on. I'm positive that when driving, that cab fuel consumption is much higher at 2k that when in Park running at 2k. I still think the generator is worse, but the comparison I believe is closer than the test results.
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Old 08-08-2015, 06:35 AM   #16
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Quote:
Originally Posted by mud yapster View Post
I don't have a MH but have as much invested if not more. My diesel engine doesn't feel the a/c and I'll run the Onan in the 5er to keep it cool for my little woman if not traveling far. As much money as I have rolling down the road and getting 9 mpg in truck and Onan uses 3/4 gal/hr is little price I pay to have her say ; sure feels good in here babe. Puts a smile on my face. LOL if we are going 6 hrs away I'll stop an hour before we get there and turn on the Onan so it nice for her. LOL She's spoiled!!!! My fault.
So am I reading this right, your wife is in 5er, going down the road? Or are you just keeping the rv cool on the short trips so it's nice when you arrive?
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Old 08-08-2015, 08:04 AM   #17
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Coach a/c vs cab a/c

We experienced our first trip by motorhome this summer to Florida.

We eventually stopped at CW and bought a DC / AC / battery (rechargeable) fan and set it on the floor just aft of the cockpit seats.

This allowed for the recirculating of the cold dash air back in the coach. To us this made scientific sense and gave us the feeling of improved efficiency.
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