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Old 11-27-2011, 10:15 PM   #1
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Dash A/C or overhead AC?

Everyday , it seems I learn more. This site plus my snooping around the coach leads to discoveries, then of course more questions.

While driving, what is more economical to use, the dash air, or the overhead AC units and of course the generator. The manual shows under 1/2 load the genny will use about 1/2 gallon an hour. I can not find anywhere, how much it drags from the engine to run the dash air.

I have 330 hp cat, and a 7500kw genny.

Looking underneath, the length of these a/c hoses on a 40 ft home, really seems inefficient. I'm willing to bet the cost of replacing the dash AC is almost s much as rebuilding a generator.

MH gets 10 mpg, gen uses 1/2 gal per hour. The faster your drive the more efficient using the genny becomes.

I can not be the first person to wonder about this.

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Old 11-28-2011, 02:57 AM   #2
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You are not the first and you won't be the last. A gas coach is more effected by a difference than a diesel coach but the general rule is that the generator and roof air conditioner method of cooling is more economical. However, there may be a time when running west late in the day, that the dash air is necessary; due to the heat load on the windshield. Good luck, enjoy and keep us posted.

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Old 11-28-2011, 09:43 AM   #3
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The dash air is a hidden load, often as much as 20-30 hp of constant power draw. You just don't notice it when you fill the tank. And the dash air won't cool the whole coach unless it is really small. In our 40 footer with a big glass "greenhouse", it barely keeps the front seat area cool.

Running one a/c on a 7500 watt genny is only about 20% load (1500 watts), so the amount of fuel used is tiny, around 0.2 gal/hour. Turn the big air on and enjoy it. We do so whenever the outside temp gets much above 80 and the sun is bright.
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Old 11-28-2011, 10:15 AM   #4
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I use the dash a/c when driving facing a searing sun. Otherwise, both overhead units are running which keeps the entire unit cool. Also, it is very nice to have the entire unit cooled down already after getting all hot a sweaty setting up. I also use the dash a/c when my dog has to sit in my lap and sleep.
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Old 11-28-2011, 10:37 AM   #5
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Originally Posted by DutchStar38 View Post
I use the dash a/c when driving facing a searing sun. Otherwise, both overhead units are running which keeps the entire unit cool. Also, it is very nice to have the entire unit cooled down already after getting all hot a sweaty setting up. I also use the dash a/c when my dog has to sit in my lap and sleep.
Ditto for us. Dash unit will not cool more than the drivers area and on a bright sunny day it struggles to do that. I run the front coach unit at least.
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Old 11-28-2011, 12:29 PM   #6
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We do it by comfort. If the dash air does the trick fine, if not we turn in the generator and roof air(s).
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Old 12-02-2011, 09:05 PM   #7
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In our Aspect 26A we run the dash air and it keeps the whole MH cool. I haven't checked running the roof air and checking the fuel mileage to see if there is a difference. I may do that the next time we take a trip. I know the genny is supposed to be super effecient when used to run the A/C.
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Old 12-04-2011, 08:30 AM   #8
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I did a calculation last summer for my 400HP DP and I think it was about 2-3% cheaper to run the roof air vs dash...not a biggie but with my 66" tall windshield the dash air definitely is worth it...!!!!
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Old 12-04-2011, 10:50 AM   #9
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In the overall scheme of things, the operating cost of one over the other is miniscule.

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Old 12-04-2011, 11:00 AM   #10
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I agree with Pairajays about operating cost. For me it is creature comfort - If it's hot I use the generator & AC unit (just like in the cold winter I'll run the furnace to keep warm). On my RV it seems to take forever for the basement airconditioning to cool the RV if it is hot inside when we arrive at our destination.
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Old 12-04-2011, 11:47 AM   #11
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We always run the roof airs, we set the bedroom a little cooler than the front air. We also when facing the sun, run the dash FAN only to circulate the cooler air up front. This helps a lot and does not put the load on the diesel.
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Old 12-04-2011, 12:39 PM   #12
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I have seen this question many many many many times.. Many argue it is less expensive to run the genny.

What I find, and yes, this will very from rig to rig, is the HOUSE air does a tripple P job of cooling the cockpit area (I won't tell you what the first P iss but the other two are POT POOR). Silibant S on purpose)

Likewise the dash air don't do much for the house.

I use dash when driving less it's really hot, then I double up. (or if it is my 30 minutes under half load day)

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