AC and mpg

I don't think the fan speed is much of a factor when compared to the power needed to run the compressor. I am sure that the A/C cuts my mileage by a lot, but I don't care. Whatever it is, it is. I haven't had mine off since our last cold spell in January. Maybe that is why I can't really match up with the numbers I see on this forum. During our "winter" my numbers were 3-5 mpg better than they are now.

I would love to see someone do a really accurate test on this, but as I said, that would be mostly for academic reasons. I am NOT turning off my air!

 

Ultimately, your car is powered by gasoline, so anything that will increase the electrical usage will have some effect on your mileage.

That said, I would not worry about cycling it on and off. I would allow the climate control system to do that. Just set it on the warmest comfortable temperate, and drive. If you were to cycle it, the extra power required to re-cool each time would eat up any savings you may get by turning it off. Additionally, if you drive your car in ECO mode, it will reduce the amount of electrical energy used by climate system, while not reducing your total power available to the wheels.

 

If you drive at highway speed, you'll get a bigger mpg hit if you have the windows rolled down rather than the A/C on.

 

The car switches the compressor on and off, and controls its speed, as necessary anyway. For best mileage, set it to the highest temperature you're comfortable with. There isn't really any need to force it to be off.

...except if you live in a humid climate and just want the car to produce heat. Then I force the compressor off, because it's trying to dehumidify the air unnecessarily (the British climate is just more humid than the car is designed for).

 

I run A/C all the time lately, and sure it affects my gas mileage but just barely. To me, losing 1 extra gallon of gas for me being comfortable driving 60 miles everyday is worth it because fillups cost less than $30.

The only time I'll turn the A/C off is if I really need the extra power, like passing on an incline or sometimes on a freeway onramp when I really need to get up to speed.

 

You won't get noticeable "extra power" when climbing if you turn the A/C off. It's completely driven by electrical power from the traction battery. That battery will provide the extra energy to the A/C when the MGs can't. If it's climbing for 5 min you -might- notice the difference, but I doubt it. But I'm sure you can imagine it's there.
The battery -can- provide -some- extra power when climbing, but again, only for a short time, and only a limited amount. It's limited by battery temperature mostly, and having the A/C set to a comfortable temperature can go a long way towards keeping the traction battery at a reasonable temperature, thereby allowing the HSD to actually use the power for your climb.

 

i notice about a 1mpg drop between my commutes with and without A/C. these are 100 mile trips on the interstate. around town running it all the time with my daughter in the car i notice about a 3-4mpg drop.

 

I see about the same 1 to 1.5 mpg drop when I run AC on my 52 mile daily commute. This time of the year I do not need the AC in the morning but do in the afternoon.

I will be glad to take the 1.5 mpg hit to drive in comfort ! Even with the AC I am still averaging about 50 mpg.

 

@joe166

I agree with you. During winter my numbers were better than now (20/25° C more now).

 

I'm hoping the switch to summer-blend gas will more than off-set the lost efficiency produced by the A/C.

 

This seems to be a dissenting opinion, but when it gets hot and humid here, I'm running the A/C.

 

Despite not being hot in London right now, I'm still using the AC as it seems to help with hay fever (along with an occasional blast on the air filter). My MPG has gone down from 50 (Winter) to 45 (Spring) but they're much more enjoyable miles.

 

Remember the A/C is not only for people but also for the HV battery. If it is too hot for you, so is for the HV battery.

As Mike has mentioned, the A/C compressor is variable speed. It even adjust itself if the car is under sun shade!

Use it if you need it. You paid for it already. Don't just lug it around.

 

Good points.

Also, while driving at highway speeds, it is better to use A/C rather than rolling down the windows, as this would break the air flow around the car and increase fuel consumption (more than what A/C does).

 

Yes.

While every car has different aerodynamics, a general rule of thumb is that <35 mph it is better to roll the windows down, >35mph it is better to use the AC.

YMMV.

 

I always get less in the winter than the summer. Warm weather, with normally dry roads, will contribute more to MPG's than 40 degree rainy weather like we have 8-9 months a year in the great northwest.

AC appears to me not to use that much gas, espically in 'ECO" MODE.

Also Oregon is a Ethanol 10% state all year long.

alfon

 

I am not sure how relevant to my situation your experiences in Oregon are. Many times I envy the temperatures I hear on the Weather Channel from Oregon. It gets beastly sometimes down here. We do have the advantage of being so close to the United States here in Miami, though.

 

Somewhat wild guess, that AC averages around 300 watts in moderate use, and double that for max use. Without AC, drivers getting 50 mpg are consuming about 11 kW at the wheels, so the AC 'hit' is about 3 - 6%

 

You have to remember that the Prius Climate Control System is not like the typical auto ac. Toyota's use of the term Air Conditioning in the Prius is technically correct, but many confuse Toyota's use of the term with the common belief that Air Conditioning refers only to the cooling of cabin air. True air conditioning indicates a fully controlled air environment.

The Prius battery requires a "room temperature" environment for most efficient operation. If the interior of your cabin is hot after sitting out in the sun, the Prius uses the climate control system to bring the cabin temp down to a level which helps the battery operate efficiently. Not using AC can also reduce your mileage.

Having to buy a new HV battery will really give you a headache.

Just set it to AUTO with the temperature so you are comfortable and let the system work as it was designed.