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Old 05-27-2010, 11:35 AM   #1
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House vs. dash A/C on the road

Just took home Georgetown 341, my first motorhome after several 5th wheels. The dealer employee who checked me out on the unit told me that it was better economy to run the house A/C with the generator while on the road than to cool with the dash A/C. This seems odd. Any feedback?
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Old 05-27-2010, 11:59 AM   #2
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I don't see how it is more economical. You have a run a second engine to make power for the house AC. Running 2 engines is not cheaper than running one, period. With that said, the dash AC will never cool the whole rig. If you ever need to get the whole thing cooler, then you will have to run the generator and the house AC. As long as you are comfortable, run the dash AC. Wait till you get to the campground with shore power, YOU ARE PAYING FOR, to run the house AC. My two cents, your mileage may vary.
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Old 05-27-2010, 02:22 PM   #3
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I don't see it as being more efficient but it may be necessary as Windrider pointed out to have to run both to cool such a large rig. Depending on several factors such as dark color full body paint and ambient air temperatures you may need to run the roof air. Remember that the truck AC was designed to cool a large car or truck, not a 34' motorhome. I have seen from others where they think this is a design flaw and poor practice that the engine AC can't cool a 35' rig which only shows their ignorance.

When things get really hot, sectioning off a part of the rig with a door or divider will help a great deal to reduce the amount of "conditioned space" you need to cool. You may also find that if it's hot enough and you have a dark rig that both ACs running may not even be enough.
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Old 05-27-2010, 06:52 PM   #4
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I haven't tried myself yet since I'm new but on rv.net they claim the roof a/c is more fuel efficient. I'm taking a trip next week and I know the dash air can't cool the whole living area so I may need to use the roof air, but we shall see I guess
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Old 05-28-2010, 07:35 AM   #5
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I prefer to take some load off the chassis engine and run the generator since it needs to be excercised anyway. At 50% load it's only consuming a little more than 1/2 gallon an hour, the fuel impact is not that great. You spent a lot of money on your rig to be comfortable camping, you should be comfortable driving also.
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Old 05-28-2010, 11:27 AM   #6
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Originally Posted by NWJeeper View Post
I don't see it as being more efficient but it may be necessary as Windrider pointed out to have to run both to cool such a large rig. Depending on several factors such as dark color full body paint and ambient air temperatures you may need to run the roof air. Remember that the truck AC was designed to cool a large car or truck, not a 34' motorhome. I have seen from others where they think this is a design flaw and poor practice that the engine AC can't cool a 35' rig which only shows their ignorance.

When things get really hot, sectioning off a part of the rig with a door or divider will help a great deal to reduce the amount of "conditioned space" you need to cool. You may also find that if it's hot enough and you have a dark rig that both ACs running may not even be enough.
Could you imagine the velocity of the air if the dash AC was designed to cool the whole coach. The wife gets up to get a drink and can't walk back to the front of the coach. She looks like she walking in a hurricane. As for the driver the frost is forming on his forehead.
We use the dash AC when driving at night and early morning but mid-day on very sunny days the genny is running with the main AC Unit. The secret is to start running it before it's too hot that the thing struggles to cool the coach down. Cooler days we may use the dash AC and open a window and run the fantastic fan just to keep it comfortable.
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Old 06-02-2010, 08:59 AM   #7
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Cfsoistman, I hope you get this. I sent you a PM and don't know if you got it but I have the Interactive Training DVD and Diagnostics Manual on R-22 and R-410A. I need to know how to get it to you.....Wade.
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Old 06-02-2010, 11:41 AM   #8
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Cfsoistman, I hope you get this. I sent you a PM and don't know if you got it but I have the Interactive Training DVD and Diagnostics Manual on R-22 and R-410A. I need to know how to get it to you.....Wade.
Sent you a reply message. Thanks for the reminder.
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Old 06-25-2010, 03:02 PM   #9
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I just got back from a trip and the dash ac was adequate for the front seats even in 100 degree heat but my 2 year old made it necessary to run tge generator about half the time. Maybe . 5 mpg difference at most
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Old 06-25-2010, 08:26 PM   #10
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We're leaving tomorrow to go home. 515 miles and we'll have the generator running with one AC on in the coach and the dash AC. It's going to be in the 90's so it should be ok with both running. Without running one of the AC units it's just uncomfortable for anyone behind the front seats.

Correction, We started out with one AC but ended up using both AC units to cool the coach. It was really a hot one on Saturday but we were reasonably comfortable on our way up the road.
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Old 07-03-2010, 09:55 AM   #11
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I'm in the middle of a 17 day trip in Colorado and had something interesting happen to me on the way out. It was 100degrees in western Nebraska and my Generac 6500 generator overheated on me running both ACs and the fridge for 8 hrs. I have a remote temperature sensor under the rear bumper close to the generator and it read 116. Granted I had not kept the generator very clean but I expect it should be able to run when I need it most. It came back after cooling for 20mins and I relied mostly on the dash AC and 1 house AC but I was pretty dissappointed. I run Mobile 1 in it and maybe I should remove the enclosure cover when it gets that hot but I'm not sure what else I could do besides add an oil cooler. Wish I had the Onan :/ Next time
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Old 07-03-2010, 02:54 PM   #12
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I'm in the middle of a 17 day trip in Colorado and had something interesting happen to me on the way out. It was 100degrees in western Nebraska and my Generac 6500 generator overheated on me running both ACs and the fridge for 8 hrs. I have a remote temperature sensor under the rear bumper close to the generator and it read 116. Granted I had not kept the generator very clean but I expect it should be able to run when I need it most. It came back after cooling for 20mins and I relied mostly on the dash AC and 1 house AC but I was pretty dissappointed. I run Mobile 1 in it and maybe I should remove the enclosure cover when it gets that hot but I'm not sure what else I could do besides add an oil cooler. Wish I had the Onan :/ Next time
Not sure if would have made a difference but we run our fridge on propane when traveling. Is there any way to get more air flow into the generator compartment?
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Old 07-30-2010, 10:13 AM   #13
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Im not sure if the generator enclosure is any different on my rig but I have an Onan 5500. this weekend I ran the gen 8 hours while driving with both a/c and the fridge going and there was no excessive heat. This was in Fla, with a heat index near 110
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Old 07-30-2010, 10:51 AM   #14
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Returning from a camping trip from hell, we ran both the genarator and A/c and the A/C off the engine in 100 degree weather. We left early from camping because the campground could only produce 103 volts (and thats with a autoformer). The camground never upgraded its electricty after a bad flood. In some cases, the voltage was down to 99.4 volts. We all were running our generators so not to damage any appliances in the motor homes. For those in Virgina, the campgrounds was call New Point campgrounds.
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Old 07-30-2010, 10:51 AM   #15
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Machines don't care about the Heat Index, only true temperatures. Heat Index combines temp and humidity into a value of how it feels to us humans. It could be 90F with 80% relative humidity and the heat index would be 113F.

On my return trip it hit 93F and the generator didn't stop for 11hrs running everything, so that was good. I hope it was just an unusual set of circumstances that caused it to overheat. Dirty, Wind direction, etc. I'm still going to go Onan on the next rig but it will probably be diesel.
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Old 07-30-2010, 11:47 AM   #16
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We just drove through Arizona and Nevada where the outside temp was 112. Obviously that's dry heat. Some of the grades were fairly steep and because of construction there were stop and go delays. The dash A/C ended up not being enough and the roof unit did a fine job of making us comfortable enough although not cold.

I suspect that the economy of which unit to run also depends on speed. If your engine uses loses 3mpg efficiency from running the additional load you also have to figure how long it takes you to go that distance. The generator uses 1/2 a gallon an hour.

I am going to investigate a curtain arrangement to divide the front and back for better cooling on really hot trips. I think a friction pole and bed sheet would do the trick.
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Old 08-06-2010, 12:25 AM   #17
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We usually run both AC's with generator running while traveling. The fuel consumption is minimal in my opinion compared to the extra comfort and needed power options for traveling with 4 kids. I saw where someone suggested removing the generator enclosure to assist with cooling. Onan will tell you that this will actually cause the generator to run hotter as the enclosures are designed to put high amounts of air in the "right" places to assist with efficient cooling and not just to reduce noise. Although I think we are discussing a Generac generator but it is worth consideration. Happy and "cool" travels to you all!!!
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Old 09-13-2010, 11:38 PM   #18
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The RV dealer tech that showed us our RV stated it would be much cheaper to run the generator with house AC than put extra strain on the engine...makes sense to me as the generator, as mentioned prior inthis thread, burns .5 gal per hour and needs to be run anyway. This is what we did but too new to have any real stats yet!
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Old 09-14-2010, 06:49 AM   #19
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We have found that we can help the coach temp somewhat by turning on the windshield fans and pointing them into the coach. This helps to take some of the front A/C into the coach. It may save you some genny time by getting this air flow going. We are also looking into getting a bigger A/C unit for the bedroom. We have found that during the day the 13.5's may not be big enough to handle the heat.
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