Your a/c vs fuel efficiency?

[Leslie]

It's already very hot here in Arkansas, over 90 and the summer isn't even here yet. My 01 classic has gone from around 45 mpg to (embarrased gulp) 36 mpg. These are short trips with some hills, etc, but still... When I drive without the air it goes back up to 45 or better. Anyone else have this situation or should I be checking something out? Do the newer models do better? Leslie in Little Rock

[tomdeimos]

AC uses a lot of power. This is normal. You need to pick the best compromise that fits you.
The ac has to go at full output to cool the car down on short trips if you let it and that uses lots of power.
The heat stored in the car can take close to a half hour to stabilize.

Same concept with refrigerators. I just go a new one and they said don't put food in it for 24 hours so it has time to cool.

You are getting a bigger hit than most people do at 90 degrees maybe. But all you can do is use less ac if you want more mpg.

1 Park in the shade.
2 Get window tinting if you can.
3 Use sun shields when you park and leave windows open when possible when parked.
4 Aim cold air vents directly at you so you can be resonably comfortable while not even trying to get the car dash etc cooled off.
5 Take longer trips so the car can stabilize and ac load goes down to normal.
6 Run fan on lowest speed you can handle.
7 Open all windows when starting out for a few minutes to get car down to ambient temp before turning on the ac. and closing windows.
8 Keep in mind your actual mpg heads down to 0 when you are stopped. So your mpg hit will likely be less when you can drive faster. For my 2005 Prius I generally find I can keep the mpg loss to 2 mpg or less if I drive 60 mph. Drive at 30 mph and it will be 4 mpg etc. (This is on trips when car has time to cool)
On short trips with a hot car that was parked in the sun I can often lose 10 mpg.
9 Get a white car next time, if yours is some other color.
10 Remember the better your AC the worse the mpg hit, unless you cut the output. My last car had almost no ac hit in my commuting, because the car had to run AC full blast all the time and on my short commute it just never was able to cool the car down. With Prius AC I can burn about as much gas as I want to be as cool as I want to be.
11 One extra thing I did was add sound insulation to the doors. I did it more for AC heat insulation than for sound deadening, and it does help noticably. Helps with keeping warm in winter too. So this year I can use less AC power and still be comfortable.

[ken1784]

<div class='quotetop'>QUOTE(Leslie @ May 26 2006, 08:12 PM) [snapback]261241[/snapback]</div>

Anyone else have this situation or should I be checking something out? Do the newer models do better?
[/b]

Following is a good article by Denso...
http://www.epa.gov/cppd/Presentations/Mats...%20inverter.pdf
On page-7, it says the 2004 Prius AC is 19% less impact for mpg than the previous model.

Ken@Japan

[daniel]

<div class='quotetop'>QUOTE(tomdeimos @ May 26 2006, 04:58 AM) [snapback]261257[/snapback]</div>

9 Get a white car next time, if yours is some other color.
[/b]

Most of the solar radiation enters the car through the windows. The body of the car is insulated. I don't believe the exterior color of the car makes a significant difference. A black car will have a hotter exterior skin temperature, but the amount of that heat transmitted through the body to the interior will not be great.

[DaveinOlyWA]

another benefit of living here. summers are relatively mild. also not driving during the hot part of the day will help. prime examples (some of the result will be mitigated by break-in and changes in technique)

2004 one of hottest summers on record. 54 mpg work hours 6 am - 2:30 pm. A/C most days. driving home during hot part of the day. speeds only 35 mph

2005 normal summer 58.5 mpg. work hours 10 am to 7 pm missing the hot part of the day rolling down windows on ride home sufficient for most days.

this summer, will be working 6 am to 5 pm so will be leaving at THE hottest part of the day. (sun sets after 10 pm here in summer) so will be hard to not use air. but will try to as much as possible. either way, averaging 56 mpg is what i expect to do.

[Leslie]

<div class='quotetop'>QUOTE(tomdeimos @ May 26 2006, 06:58 AM) [snapback]261257[/snapback]</div>

AC uses a lot of power. This is normal. You need to pick the best compromise that fits you.
The ac has to go at full output to cool the car down on short trips if you let it and that uses lots of power.
The heat stored in the car can take close to a half hour to stabilize.

Same concept with refrigerators. I just go a new one and they said don't put food in it for 24 hours so it has time to cool.

You are getting a bigger hit than most people do at 90 degrees maybe. But all you can do is use less ac if you want more mpg.

1 Park in the shade.
2 Get window tinting if you can.
3 Use sun shields when you park and leave windows open when possible when parked.
4 Aim cold air vents directly at you so you can be resonably comfortable while not even trying to get the car dash etc cooled off.
5 Take longer trips so the car can stabilize and ac load goes down to normal.
6 Run fan on lowest speed you can handle.
7 Open all windows when starting out for a few minutes to get car down to ambient temp before turning on the ac. and closing windows.
8 Keep in mind your actual mpg heads down to 0 when you are stopped. So your mpg hit will likely be less when you can drive faster. For my 2005 Prius I generally find I can keep the mpg loss to 2 mpg or less if I drive 60 mph. Drive at 30 mph and it will be 4 mpg etc. (This is on trips when car has time to cool)
On short trips with a hot car that was parked in the sun I can often lose 10 mpg.
9 Get a white car next time, if yours is some other color.
10 Remember the better your AC the worse the mpg hit, unless you cut the output. My last car had almost no ac hit in my commuting, because the car had to run AC full blast all the time and on my short commute it just never was able to cool the car down. With Prius AC I can burn about as much gas as I want to be as cool as I want to be.
11 One extra thing I did was add sound insulation to the doors. I did it more for AC heat insulation than for sound deadening, and it does help noticably. Helps with keeping warm in winter too. So this year I can use less AC power and still be comfortable.
[/b]

Thank you and everyone for thir insights and advice. I'll do those recommended things. I also have to remember that even at its WORST, with the AC on and me comfortible, I am getting 250% better mileage than my recent Jeep Grand Cherokee- and I'm having more fun driving. It really is so easy to get fixated on just gas mileage. Leslie in Little Rock

[mikepaul]

Almost all my best reported MPGs were with the A/C on. How sticky the tires are has always made more difference.

I'm trying my best to extend the fan life by only using heat or cooling when I'm uncomfortable, but that probably ends for the season this weekend when every moment I'll be in the car, it will be too hot to go without.

Maybe by November, I could go without some cooling...

[iaowings]

I know this kind of sounds harsh. Try 78- 80 degrees with auto ac on. I know for me I don’t even use the ac utile it’s over 80 with the humidity around here u cant go much over 80 without suffering. However, the ac takes care of the humidity so 80 isn’t to bad.

My biggest complaint is that when people ride with me as soon as they see sunlight they want the ac on max cool all the time

[tomdeimos]

<div class='quotetop'>QUOTE(daniel @ May 26 2006, 09:00 AM) [snapback]261264[/snapback]</div>

Most of the solar radiation enters the car through the windows. The body of the car is insulated. I don't believe the exterior color of the car makes a significant difference. A black car will have a hotter exterior skin temperature, but the amount of that heat transmitted through the body to the interior will not be great.
[/b]

I disagree strongly with this statement. I had a black car previous to the Prius and I will never own another one even though I like the color. My Prius is not white, and also has more window area but is much cooler when I get into it than my old car was when I park in the sun on a hot day.

I do agree while driving most heat comes in the glass area, but parked and using a sun shade, a big part of the heat is through the body of the car. I have melted plastic in my trunk in the black car, and just testing cars trunks in the parking lot a work I found thw white ones were noticably many degrees cooler.

Keep in mind here we are talking about short trips. On a long trip the AC load decreases to a reasonable level, and fan speed goes down to a low speed, but on my commute it doesn't get much below full output unless I limit it. I have often lost way more than 10 mpg due to AC during commutes, but on trips I rarely lose more than 2 mpg. from AC use.

[DaveinOlyWA]

have to side with Mike on this one. i lived in the south enough to know that driving without A/C simply aint an option no matter what color the car. just the tradeoffs you have living just about anywhere. you will get it back this winter when im doing 45 mpg and you are still at 50