I am sure that someone has done the research on whether you get better gas milage using the dash engine air or running your generator and using the roof air. What say you guys? I have a gas engine on a 34 foot class A.

We have run both ways, and we have absolutely no proof, but we think we get better gas mileage running the roof air with the dash air off. However, the cockpit does not cool off as well with just the roof air. And sometimes it has been so hot we have run both at the same time. That sure ruined our mpg but our comfort was worth the price. I can say that we have had service techs and salesmen tell us that it is more efficient to run the roof air. Maybe someone else has done some comparisons.

If we are in the dessert or at times here in FL and the heat is high we run dash A/C and generator with two roof A/C units on. We use all diesel fuel and can not see any change in mileage. Diesel generator has a use rate of 3/4 gal per hour at full load (66 amps). We have a 150 gal tank so you would see little change in mileage. You may only need roof units on couple hours or so.

Thanks Jon I use regular gas. I am in The Villages here in Fla

Bud,

That is a nice place to live, we like it also.

I did a little math and came up with these numbers. Lets say w/o the dash air you avg 9 mpg. The generator burns a gal an hour. To cover 60 miles, you would need 6.67 gals of gas for the engine and 1 gal for the generator.
If you turn on the engine AC and turn off the generator and your mpg falls to 8 you would need 7.5 gals to cover the 60 miles. About the same. Would make sense to run the generator if your mpg falls more than 1 mpg when you turn on the engine AC. At least that is my best guess

Don't you guys watch "Mythbusters"?

They actually did this using an SUV but the principle is the same.

Windows down and no A/C beat windows up with A/C.

They also did an episode about tailgaiting an 18-wheeler inorder to draft and save fuel and the results were amazing (and frightening).

They saw about a 60% reduction in fuel usage. O'course they had to get to within 2 feet of the rear bumper or a tractor trailer.

They have a lot of useful information on that show. Like what's the quickest way to cool a 6-pack.

Hi,

Mythbusters revisited AC vs windows down and at the speed they were driving it was cheaper "windows down" but--at 50 MPH (80 kph) the opposite was true.

I did an experiment on my most recent trip (5000 kilometers) and found no difference in mileage whether I was using my generator and roof air vs dash air. The variation s were Roof air only, dash air only, and both together. YMMV *grin*.