air conditioning and mpg

it calculates how much gas is being used and divides it by how many miles you went...

Eveything gets counted in the LCD mpg readout.

So yes, if you turn on the AC, it is still giving you accurate readings of mpg.

The AC doesnt affect mpg much due to it being electric


Note however, the average MPG display is on average, 2mpg+ the actual mpg.

 

I would have to disagree that the AC doesn't affect MPG much. It would affect MPG just as much as driving in EV would. The electricity the AC uses has to come from somewhere. At least with EV, you are moving and temporarily improving your miles. With AC, you are just using electricity but going nowhere.

Now I will grant you, you are using LESS gas overall than a conventional AC. Even at full speed, the AC compressor is more efficient than a conventional system, plus it adjusts its speed to demand. So when the only demand is to maintain existing temp, it runs much slower. A conventional system would run the compressor to maintain about 40 degrees at the evaporator, even if that means your cabin would be too cold. You would compensate by adding heat.

So, you may not see your MPG affected right away, but it will be negatively impacted.

 

How soon we forget winter LOL!!!!! I run my AC all the time just to be glad the damn snowflake is finally out and my summertime mpg's are back!!!!!

 

I hope this thread does not go toward the "avoid a/c because you loose 1 or 2 or 3 mpg". That advice is pointless and not particularly good. Here's why.

First, the traction battery uses cabin air for cooling. The air in the cabin doesn't have to be frigid for it to effectively remove heat from the battery, however you can't have an ambient temp in the cabin that is the same as a very warm summer day and have the battery continue to run efficiently. In short, the HV battery is happiest when the cabin temperature is comfortable for the passengers. I like to keep my cabin at 73 or so in the warmer months and 68 or so in the cooler months. The HV battery is happiest between about 65 and 80 degrees. Much beyond that and the battery starts to warm up and become less efficient.

You will take a larger MPG hit if the HV battery isn't cooled to a comfortable operating temperature. As the battery temperature increases, it looses efficiency, and then the gas engine has to work harder to keep the car running and to charge the battery. Not an advisable situation.

A rather long time ago I once had a very intelligent Lincoln-Mercury service manager say that a/c was a use it or loose it device. If you used it you would see fewer service calls for a/c, fewer charges in the lifetime of the car and in general better a/c service. This was because oil is circulated through most a/c systems, both lubricating the compressor and also keeping seals and o-rings moist and fresh.

So, do not hesitate to use your a/c. Your car depends on you to do it.

 

Does anyone know how many watts the A/C compressor is rated at or how much current (Amps) it takes?

 

<div class='quotetop'>QUOTE(jeromep\";p=\"97341)</div>

I think I'm seeing this lately. The MPG loss due to the new tires has me happy over every small recovery, and since this weekend I've lost a few more MPGs, driving the same places I had been driving. Climate has been the only real variable, so when the battery is happy, I guess I'm happy.

I do run the A/C all the time, but I've been adjusting the set point to have the fan run the least. Perhaps more fan all the time will help more...

 

<div class='quotetop'>QUOTE(\"jeromep\";p=\"97341\")</div>

Jeromep- You are a smart guy and I respect your opinions, but.....I did a test on this and have concluded that even though this seems perfectly reasonable, testing results do not concur.

On my last tank, I kept a spreadsheet that monitored individual trip mileages. I drove the same route home every day. I drove the same speeds and the temperatures were the same. On the first half of the tank, I left the windows down until I was on the highway to avoid depleting the battery at traffic lights. Once on the road I set the AC between 78 and 81 degrees. Outdoor temps were in the mid 90s. On the second half of the tank I did not use the AC at all. I left the window down six inches on the drivers side. The mileage with minimum AC use was 55-56 MPG. The mileage with no AC use was 62 MPG. The numbers prove to me at least, that AC uses more energy than it saves.(comfort issues aside) Rolling the window down some for air is a much smaller hit on mileage than using the AC.

I am not advocating not using the AC in mid 90 degree temperatures. This was simply a test and helped me to achieve 818 miles at 65.1 MPG. My morning commute is much better for mileage. I will post pictures and the spreadsheet on a separate thread.

Again, I am not advocating discomfort for mileage. When I drive normally conservative with comfortable cabin temperatures and no limit of short trip, I get 58 MPG and 650 mile tanks. The extra 7 MPG is not worth the limit on comfort. It was just a push the limit kind of thing that I enjoyed doing for the last three weeks.

 

Thanks Ray, now I don't feel so bad about my lower numbers. Too hot and humid for me to keep the AC off, even in the morning.
Soon, October will be here, and higher MPGs will return.

 

I'm guessing that much of my less than stupendous mileage is due to my using the AC often in a non-moving WAITING mode! Waiting for my daughter to "quickly run in and back out," waiting to pick up a friend who "will be ready as soon as you call me to say you're out front," etc. I try to help by waiting as fast as I can...

 

I consistantly get better gas mileage the warmer it is outside and when it's warm I always run the air conditioner. I've driven to Las Vegas and Phoenix from Los Angeles in 100+ temps, driving 70 with the a/c at 74 and gotten my all-time best mpg, 50+. I don't get that kind of mpg when I drive there in the winter without the a/c blowing, usually around 45mpg - 46 in the winter. Go figure.

 

<div class='quotetop'>QUOTE(kuahinahina\";p=\"102872)</div>

Oooo, I hate that! If you know I am coming, BE READY!

 

Guys,

I'm new here. I just found the forum today and registered. I had my Prius since October of 2004. I think I have noticed a drop in milage with both extreme heat and cold. I usually get 50-51 MPG. The last tank of gas it's droped to about 47. The temperature has been in the lower 90's. It sounds like you guys blame the traction battery loosing efficeincy with temperature extremes. Any other thoughts?

Al K.

 

Al, Welcome to PriusChat. You will find a lot of info here. And a lot of nice people.

As for the AC, the Prius uses gas to make all it's energy. Even the regen energy from the brakes got there from gas. The electricity in the batteries got there from gas.

An AC uses energy. Thus of course it affects the gas that the car uses. In fact, I would suggest that the Prius takes a BIGGER hit from the heat and the cold because most cars are overpowered and the engine is constantly making more energy the entire time it is running. Some of that excess energy goes into making heat and running the AC. Thus, the heater being on or the AC being on only increases energy use a little bit, hence a smaller hit on the MPG.

But the Prius is designed to NOT make too much excess energy, and it uses a lot of the excess energy that the car does make, and uses that energy to make electricity to be used later.

That is the key to the Prius. Toyota has designed it to make more efficient use of the gasoline in the tank.

But the effect of that is when you increase the load on the car, with the heater or the AC, the car uses some of the wasted energy -- that would under other circumstances go to making electricity -- to deal with that load.

Hence the hit on your MPG.

But this is not a defect of the Prius, it's a defect in all the other vehicles out there that takes the hit all the time, not JUST when there is an increased load.

 

Prius04,

Yep.. As an engineering level electronics technician I think I have a pretty fair graps of the way the energy is used and reused. I am just looking for as may details as I can find. I should buy the technical manual on the car but got a bit of a side-step when I asked about it at the dealer where I baught it. I just haven't been back to try again!

The air conditining obviously uses power that can only come out of the gass tank, but why would the milage go down when it's cold? That heat is taken from wasted energy casued by the normal operation of the gass engine? That heat should always be there since no gass engine is 100% efficient. Degradation in tranction battery efficiency in cold weather makes some sense to me. The again the cold weather was when the car was brand new. I got it in October. The milage may have simply improved becasue the car is broken in now. Has anybody else noticed recuced milage in cold weather besides me?

Al K.

 

We, too, find that we like to put the car in park (emergency brake on) and leave the a/c running while we go in to pick up my elderly mother so the car is cool when we get back in it, as well as other times while waiting for someone. Is there any negative effect to the car or the a/c to do this? Doesn't seem to affect the mpg any. How long at a time would it be "safe" on the system to do this? Have been wondering about this since with the 90+ temps it is tempting to do this often.

 

I think I have the record now for low mileage in a Prius. I got about 4 bars in a row of about 5 mpg each.

My record low mpg was due to a trailer truck that flipped and I got stuck in a line of cars going 0 mph in 94 degree weather. Every five minutes we'd move about a car length. I ran the AC set at 78.

On trips at 65 mph I can run the AC no problem with a cost of maybe 2 mpg.
Normal commuting the cost is more like 5 mpg since the car isn't fully cooled by the time I get home. And on the back route going slower the cost goes up to maybe 10 mpg.

Cover less miles and the AC cost goes up in proportion in mpg terms. A faster car may have more heat load, but AC runs more efficiently too, so that pretty much cancels I think. So your ac load is over time not miles.
Doesn't matter if the gas you burn to keep cool was over 2 miles or 200 miles.

 

I haven't had my Prius long enough to come up with exact figures, but the a/c seems to take about 4 mpg. Since my wife refuses to drive without a/c, I'm still pleased as can be in her first tank - averaged 52.2 mpg. I drove the Prius in the evening yesterday without the a/c and I had my best ever 5 minute segments - the first at app. 80 mpg, the second segment at 100 mpg! That was with no a/c on a 35 mph road with a slight downhill the entire time.

 

I’m from the Northern VA area where the humidity is, well, pretty high.

Initially I tried to run the AC minimally, and drive at the exact posted speeds, to get the best MPG. My best tank was 56.7! I was happy with that. My

However, I gotta have my AC so I put it on 72 with the fan on medium. Lately I’ve had to spend a lot of time on the cell phone while driving - so I haven’t used the same attention getting good MPG that I’m able to spend when I’m not on the phone (wish I had Bluetooth!!). Over the last two tanks I’ve only got 49 and 50 MPG’s, but my average is 52.+.