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It is my understanding that the AC is an electric compressor not an engine driven one. If this is the case how would having the AC on affect your milage as in a normal car it is driven by the engine and you can feel the engine bogs down when you start the AC but not in the Prius. So would some one explain this to me how does the AC being on affect the milage?
 

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Because you may have to run the engine (ICE) more to recharge the battery.

On the other hand, using the AC may ultimately not reduce MPG if the cooler air inside the cabin allows the car to use the batteries more efficiently or if you would otherwise open the windows thus creating more drag.
 

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Just as you see lower MPG when the battery SOC is under 6 bars. You only have 2 sources of electricity: ICE, and braking. I don't suppose you operate the AC only when you stop.

Now the reason it doesn't necessarily bog down the ICE when you accelerate, is because it can use the battery as a reserve to maintain the AC, while the ICE accelerates you. However, if you are attempting to get max power out of the car, again only 2 sources of acceration power: ICE and battery. If you are trying to get the max power out of the battery to add to ICE for max acceleration power, then "robbing" electrical power for AC WILL bog down the system.

In a conventional car, the AC will bog down the engine directly. No reserves unless you turn off the AC during acceleration.
 

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The record setters did not use AC. I've done extensive testing and find about a 10% mileage penalty with minimal AC use in mid to upper nineties compared to rolling the windows down about 3 inches for air. That's not comfortable but does prove the point to me at least that AC has not benefit to mileage compared to it's penalty.
 

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BIGGUY said:
It is my understanding that the AC is an electric compressor not an engine driven one. If this is the case how would having the AC on affect your milage as in a normal car it is driven by the engine and you can feel the engine bogs down when you start the AC but not in the Prius. So would some one explain this to me how does the AC being on affect the milage?
You are only partly correct.

Prius prior to the 2004 model year had the AC belt-driven off of the gasoline engine. If the AC compressor is on (AC button on or front windshield defroster position chosen for fan direction), then the gasoline engine must be on. However, once at temperature the AC compressor can come on and off (and therefore turn the engine on and off) as needed to dehumidify and recool the air, unless you have the MAX AC button pressed. So, if you're doing a lot of highway driving you won't really notice the difference with the AC on, but if you're stuck in a lot of slow'n'go traffic, you'll find that the AC will be making your gasoline engine come on when otherwise you'd be sitting in electric. (The engine being on to power the AC won't show up on the Energy Monitor, unless the engine is powering the wheels or recharging the hybrid battery while it's at it, which it'll probably do since it's on...)

The 2004-? Prius introduced an electrically-driven AC. The AC is powered by the hybrid traction battery. So, if you're stuck in the slow'n'go traffic, your engine won't be forced to come on just to provide you with added cooling/dehumidifying. However, if the hybrid battery is discharged enough through AC use, the gasoline engine will come back on to recharge the battery...

Overall, I don't see any MPG advantages to the electric AC, compared to the belt-driven AC... But in either case, the AC usage will lower your MPG.

I'll note that the EPA testing does not use AC.
 

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I drive to work at 6 AM when the temp is in the sixties or seventies and home in the early after noon when it's been in the mid eighties to low ninties. My A/C stays on auto and is set to 75. I have not noticed a big difference in milage beween the two trips. Of course I have the luxury of parking my car inside at work so I don't have the burden of cooling down from say 120 or 130 degrees. For folks who have to park outside in hot climates I'll bet those sun shields and car covers pay for themselves pretty quickly.
 

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Washington State MPG

I drive a 05 in Washington state where you hardly ever need the AC. I now have 6000 miles on the car and all my milage (except for one tank full) have been between 57 and 59 mpg. Very seldom do I drive at night and leave the lights off during the day time. The driving is mostly up and down hills and my driving is about half and half city and freeway; 65 mph on the freeways. I keep up with the other traffic during acceration etc.
The one tank that dropped my milage to 55 mpg was during a warm spell (temps in the upper 80s) and I decided to try driving with the lights and AC all of the time.
So you can see what the lights and AC can do to mpg in a controlled enviroment.
 

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I live in the oft ignored Eastern half of Washington State where A/C is a requirement. Our days have been in the high 90s low 100s. There is a mileage penalty for using A/C, but I find it insignificant. Right now, I'm getting 47.4. My previous tank average was 47.7 and the weather during that tank was in the high 80s, low 90s.

I certainly wouldn't consider my experience conclusive, however I do believe that the impact of electric A/C is less than belt driven A/C. The addition of the variable speed compressor allows the HVAC system on the vehicle to have the A/C system operate only at the level necessary to maintain the A/C set point. It is a truly brilliant system.
 

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jeromep said:
I live in the oft ignored Eastern half of Washington State where A/C is a requirement. Our days have been in the high 90s low 100s. There is a mileage penalty for using A/C, but I find it insignificant. Right now, I'm getting 47.4. My previous tank average was 47.7 and the weather during that tank was in the high 80s, low 90s.

I certainly wouldn't consider my experience conclusive, however I do believe that the impact of electric A/C is less than belt driven A/C. The addition of the variable speed compressor allows the HVAC system on the vehicle to have the A/C system operate only at the level necessary to maintain the A/C set point. It is a truly brilliant system.
Washington state has an Eastern half? :wink:

I'm in Portland, where we don't OFTEN need the AC, but I have needed it quite frequently recently. (Highs in the high 80s to 90s, and I tend to park in the sun. I have a windshield shade, and it helps, but not enough to warrant using no AC.) That, and I'm a wuss. I can barely tolerate the mid 80s. That, and during the winters, I use the defogger almost every day in the morning. (Although I only need the AC on rarely after that, and then only on the REALLY rainy days.)

I've started to experiment with using the AC not on Auto, but on manual with the following settings: Recirc, 'face' only, fan speeds 1 or 2. Then I only run it for a minute or two at a time, or when I'm going downhill such that I'm regenerating battery power anyway. I just started this (along with using the 'Pulse and Glide' driving technique as much as possible,) with my new tank of gas. In a week I'll see how this affects my mileage. It's been good so far, though! Oh, and I used to always drive with the lights on, even during the day, and I'm leaving them off as much as possible this tank.
 

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consult needed

ehurtley wrote:

>>>
I've started to experiment with using the AC not on Auto, but on manual with the following settings: Recirc, 'face' only, fan speeds 1 or 2. Then I only run it for a minute or two at a time, or when I'm going downhill such that I'm regenerating battery power anyway. I just started this (along with using the 'Pulse and Glide' driving technique as much as possible,) with my new tank of gas. In a week I'll see how this affects my mileage. It's been good so far, though! Oh, and I used to always drive with the lights on, even during the day, and I'm leaving them off as much as possible this tank.>>>>

Ehurtley, have you visited the "MPG junkie" thread? I think the Polar Bear can help you.

More seriously, here's what I finally did: just set the AC to "auto" at about 73F, set to outside air, and let Eeyore do the rest. I found it hard not to fiddle with this button or that, but it works (all of this assuming that you can park in the shade).
 

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I think there's not a heck of a lot of difference in MPG hit between the high-efficiency A/C unit used in the Classic Prius, and the electric A/C used in the HSD, but the one major difference is that on the Classic Prius, when the A/C is on and it hasn't reached temperature, the car is a slug.. It feels the same as if the battery were very low- ICE has to rev to high RPMs, and the car has no power because it's all being stolen by the A/C compressor.. Once the condenser has reached temperature, and the compressor can just cycle on/of briefly, things are much better, but that initial "pump-up" period is just hell on driveability of a Classic Prius.. The all-electric design of the new A/C eliminates that start-up hit unless your battery happens to already be in a low state (but then the ICE would have had to charge anyways)..
 

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C4 - I don't have that problem with my classic, it does not act as a slug with the A/C on. Perhaps you had some other problem with yours. I notice a slightly increased rpm of the engine for the same power output - just like in any other car but hardly to the degree you describe.
 

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Kriby,

I have always wanted to drive a Classic Prius and get a good play with it and see how it differs, etc. I would definitly want to see how the A/C works and how it affects performance.

Just about every car I have driven has had A/C and I can usually tell when the A/C compressor has kicked in. The car wouldn't necessarily become a dog, but you could tell that there was an additional load on the engine and it was compensating for that load. I usually noticed by hearing clicks under the dash associated with a momentary change in RPM as displayed on the tach on the dash. Even though a vehicle may not become a dog with belt driven a/c engaged, there is some engine hit. It all depends on how well the engine computer compensates with air flow and fuel adjustments.

I can see where C4 is coming from with regard to a vehicle's driving dynamics changing when a/c is engaged. I have driven vehicles where the a/c does present quite a load to the engine. However that has not been the majority of vehicles I have had experience with, usually just the underpowered domestic 4 cylinders from the Regan administration.

The beauty of the electric a/c system in the current Prius is that it doesn't present a mechanical load on the engine. The load is electrical. So, there is going to be an inefficiency in converting electrical power from ICE power, however with the combination of residual ICE charging when cruising and regenerative braking, I can see how electric a/c is much more efficient than belt A/C, at least in the grossest least technical terms.
 

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I have to believe that individual experience with MPG changes with A/C will vary greatly. Personally, I average 52-54 MPG almost every tank, A/C or not. When it goes below 40, the MPG goes down to 50-52. That seems to be because the engine has to come on to provide the heat when it otherwise wouldn't. I assume the same principle applies to A/C. It seems to really depend on how much "wasted" energy is recaptured via hills and braking. If you are mostly in the middle range of SOC, then I don't think there is any noticeable hit at all. Of course, if the engine has to come on, just to charge the battery due to A/C usage, then that will get added directly to the G in MPG.
 

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Running the AC doesn't seem to effect the mileage in my car much because I keep the fan speed low. It seems the higher the fan speed, the more electricity you use. I keep my fan set on the two lowest speeds and usually set the temp to 79 or 80. That works just fine for me even on 100 degree plus days.
 

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That does not seem to make sense to me. A fan uses very little energy when compared to a compressor. Keeping the air moving, by using high speed on the fan should allow you to feel cool at a warmer temperature which means you should be able to use the compressor less. I would think the energy savings in not using the compressor as much would more than off-set any increased power needed to run the fan at a higher speed.
 

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Yes, but when the fan is moving more air, there's more heat exchange and condenser warms up faster, and then the compressor has to run more often to keep the condenser cold.. By moving the minimum amount of air necessary to feel comfortable, the condenser stays colder longer and thus the compressor runs much less..

Now, the auto fan speed should in theory produce the optimum balance between speed of initial cooling and energy use, but that also depends on what the temperature setting is.. By manually forcing the fan speed to low, you reduce the compressor requirements to the minimum possible regardless of temperature setting.
 

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While that may be true, I think you will feel cooler and use less energy if you run the fan at the highest possible speed and set the temperature higher than if you set the fan low with a low temp. The high fan causes moisture to evaporate off your skin which makes you feel cooler, thus able to be comfortable at a higher temperature.
 
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