Hey Flossie, welcome to the forum. Can't see how an A/C can save milage in either application. In a car you are running a compressor with your serpentine belt when the A/C is on and that takes extra fuel due to increased power required to run the compressor. In an RV, I take it you mean a class A/B/C motorhome, it takes more fuel if:
a. you are running a conventioal car type A/C (above applies)
b. You are using an on-board gas powered generator to run your roof/basement motorhome A/C
c. both a. and b. A/C's are used
In all cases it is going to require some type of a fuel powered airconditioner to cool your car or RV unless you rely on open windows or some form of solar power/inverter to run an on- board motorhome A/C while driving down the road.
Not sure if any of that makes sense, but I tried. :bleh:
DL, that all sounds right, but I can't turn my compressor completely OFF anyway! There is no setting that will make it stop cycling. My Chev 1500 PU has been this way from the git-go. They said it was designed this way.
I am assuming that you are thinking of using the a/c in your car rather than to open the windows? Studies do say that is true, although I have never tested it. I would suspect that in a motorhome it would be a very small difference and probably not detectable. The reason is that the motorhome uses far more fuel just to move it down the road and the share of fuel needed to run the a/c would be far less, even though the actual amount might be the same. The impact on a car that gets 20 or more mpg will be much more noticable than it would be for an RV that gets between 7 & 9mpg.
HeyTexasClodhopper, does your compressor have some kind of clutch that engages/disengages your compressor. All I really know is when you are driving a small 4 cyl car and kick on the a/c the car slows down until you press on the gas pedal. Got to use more gas. :bleh:
Hi Flossie, Most cars nowadays have some sort of aero-dynamic design, so when you open a window, yes there is a difference. Motorhomes though, well let's face it, for the most part, there about as aero-dynamic as a shinny brick. Gas powered rigs will feel that compressor, especially under a heavy load. Diesel pushers don't usually have a problem.
Actually, the front of motorhomes or semi's that have flat front ends aren't that bad with aerodynamics. I went to a conference one time that included a session on design. When the motorhome or truck is going down the road the flat front creates a spaces that causes the air to seperate. Don't ask me to explain that but according to the presenters at the conference this design is more aerodynamic than having a nose sticking out in front. Not being an engineer I didn't quite grasp why.
I think the main thing to save gas is getting your heavy foot off the pedal. I have been beside motorhomes stopped at a light and listened to the driver take off like he was drag racing. Why? You will get just as far if you just slowly accelerate and let the transmission shift you up to higher speeds.
People I work with have asked me what kind of gas mileage I get with my 8100 GM engine. I don't know. When I bought the thing I sort of felt like the fella who bought a new Rolls Royce. When he ask the salesman what kind of gas mileage it got the salesman said, "If you need to know that you don't need to buy the car." I know it cost me over $400.00 to drive it from North Carolina to Michigan last month. A trip of 784 miles with gas at $3.15 a gallon. Don't you just love it.
Mythbusters did a test on driving with A/C verses windows down in Expiditions and found that they get better gas milage with A/C on. Did another test with Tailgate up and down on pickups. Tailgate up got better gas milage. Seams that the tailgate gives an air cushion that runs in a circle from top of truck cab to tailgate and keeps the air flowing in a better path. Ever seen the peice of paper that keeps going from the tailgate to the cab in a circle?
Come to think of it I have seen a piece of paper doing that. Until the cop got behind me then it blew out on the side of the road. Had to stop and get it or be accused of littering. Just trying to be funny.