It may be an old question on fuel economy.....?

I thought the most fuel efficient mode was with the A/C set to "auto". ECO may help in achieving higher MPG because of slower reaction to pedal variations but "auto" I though controls the fan speed and limits the a/c operation at times.

 

AC will not run with Auto pushed, if the AC button is not pushed. With one exception: if mode is set to Heat/Defog, then AC can run, on the sly. Depends on temps, maybe humidity too? Other than that, if you've just hit Auto, and the AC button is off (button not lit), AC is off.

This is from monitoring the compressor via ScanGauge.

 

I will try once more. All external energy in the Prius comes from the gas in the tank. I have never disputed that. What I dispute is saying using the battery lowers mileage. Using it correctly will increase mileage substantially. There are two internal energy sources in the Prius- the engine and the battery. The battery is charged by the engine and by the regeneration systems. The energy that is regenerated comes from the kinetic energy of the car. The kinetic energy is the result of gasoline burning in the engine with a small amount burning to charge the battery, from time to time. This is the only battery energy that is connected in any way to the gasoline. The rest of the gasoline energy is used to accelerate the car and maintain a certain velocity against the friction forces. That accounts for all of the external energy used in the car. There isn't any left to be charged against the regeneration system because the two events are unrelated, thermodynamically. If (as I noted in my original post) you are in urban traffic, almost all of the battery energy comes from the regen systems. Even with some charging from the engine, it is by far the cheapest energy source in the car. Using it wisely (not room here for that conversation) will result in much better mileage. I am 500 miles into my current tank and am getting 65.8 mpg...which is pretty typical during warmer weather. I live in a pretty hilly area and drive about 80% suburban/country roads.

 

Mikefocke,

Someone else can explain it better than I can, but I've heard that in ECO mode the A/C runs differently. I believe it will run at a lower power setting and cool the cabin slower than when in Normal, even when the environmental system is in full Auto Mode. Auto A/C will maintain the set temperature, but how it gets there is different.

 

We are so close, let me alter your sentence: What we saying is using the battery for any other use than propulsion, lowers mileage, because it could have been used to propel the Prius. (again barring the rare 'long descent causes engine braking' scenario)

 

BWilson4web got 100 MPG for 1,000 miles traveling at 25 MPH with the cruise control on. The Prius sure does have the ability to get some great mileage, depending on how it is driven. I believe the advertised mileage 48/53? is based on a typical person's driving habits (government rules for figuring MPG).

Here is a picture of my EngineLink HD IPad app. You can see the AC pump load is 2.15 HP while driving at 55 mph. With this AC load, the ICE is working harder to keep the TB charged than it would be with the AC off.

 

All I can picture is the steamed up parade behind him.

 

Way back when, cars had 4/40 air conditioning. Open 4 windows and drive 40mph. Above 40 I imagine aerodynamic drag will be an mpg killer, perhaps at even lower speeds than that. As others said, there isn't the usual drain from the a/c belt etc..