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Old 08-24-2014, 12:00 PM   #1
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Running Coach A/C vs. Cab A/C While Driving

There have been discussions about running the generator and coach A/C versus using the cab A/C. Although the need to cool the coach for passengers is an overriding reason to run the generator and coach A/C, some have mentioned the possibility of doing it to reduce the load on the chassis engine or to save gas.

We have a Sunseeker 3100 on a Ford E450 chassis with a V-10, and I checked the fuel flow with a ScanGauge II to see how much difference the A/C actually makes. Here’s what I found with the transmission in park and an outside temperature of about 90 degrees F:

Idle speed, A/C off: 0.55 gallon per hour
Idle speed, A/C on: 0.67 gallon per hour
2000 rpm, A/C off: 1.85 gallons per hour
2000 rpm, A/C on: 2.02 gallons per hour

2000 rpm was the best speed I could hold by reading the tachometer. It is about the rpm at 50 mph, and I usually drive faster than that, but it gives an idea of the A/C compressor load at normal speeds.

Since the additional gas used at 2000 rpm with the A/C running is only 0.17 gallons per hour compared to about 0.5 gallons per hour for the generator, it is definitely more economical to use the cab air only, if that will give you the cooling you need. As for the horsepower load on the engine, the additional 0.17 gallon per hour equates to only about 2.5 horsepower.

The cab A/C does add to the engine cooling load, but we have towed a 4000 pound car in 95 degrees up a grade more than 7% at 45 mph for more than 5 miles and the engine coolant temperature gauge never moved.
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Old 08-24-2014, 08:23 PM   #2
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Thanks for all that info.
I'm a fan of dash air while traveling
I just can't get myself to put hours on my gen that aren't necessary.
I know they are meant to run and I'm not afraid to run it I just like the idea of saving it for when we need it.
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Old 08-24-2014, 08:32 PM   #3
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I like the dash air also when I am driving and the dw dogs have to have air so in hot weather I run both.
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Old 08-24-2014, 09:56 PM   #4
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Old 08-24-2014, 10:03 PM   #5
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Great analysis info, thanks for sharing
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Old 08-25-2014, 01:41 PM   #6
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I wonder in terms of tonnage, figuring it like your home's a/c system which is larger? The cab a/c or the unit on the roof, assuming you only have one unit up there?

We usually keep our generator running because of the other appliances we keep running, mainly the fridge. So we keep the coach air running, my concern is if the cab air will cool a 32 foot coach in Texas heat?
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Old 08-25-2014, 07:08 PM   #7
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Quote:
Originally Posted by howzball View Post
I wonder in terms of tonnage, figuring it like your home's a/c system which is larger? The cab a/c or the unit on the roof, assuming you only have one unit up there?

We usually keep our generator running because of the other appliances we keep running, mainly the fridge. So we keep the coach air running, my concern is if the cab air will cool a 32 foot coach in Texas heat?
Sorry, but I don't know the tonnage of the cab A/C system.

During our first long trip we drove through west Texas in 104 degree heat. The two of us were okay up front, but when we stopped it was hot in the coach. It took several hours to cool it down once we were plugged in at the campground. In retrospect I should have run the generator and coach A/C for at least the last few hours on the road.
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Old 08-25-2014, 08:47 PM   #8
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Sunseeker's Dometic fridges will run on propane if 120 volts is not available for heat. They default to 120. They use 12 volts to control the fridge.


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Old 08-26-2014, 02:27 AM   #9
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We run ours non stop. The cab air helps the driver and that's it IMO. I can't stand the wind noise or buffeting with the windows open. We even leave it running when we stop for a sit down lunch or dinner at a restaurant. Nice and cool when we get in. We bought ours to travel in comfort.


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Old 08-26-2014, 09:10 AM   #10
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In most cases the cab AC can keep the driver and passanger cool. But on a hot sunny day, the rest of the coach is super warm. So I would have no choice but to run the genset and AC and deal with the hit. It was a lot better then having to deal with passangers behind me complaining about the temps.
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