Which AC setting do you think is best?

natural_tools · 07-25-2005, 11:49 PM

Living in Dallas, there is no way to avoid using the air conditioner in the summer. So while I'm sweating in my black hybrid oven, I'm wondering...

which AC setting is the best for MPG: low temp with low fan or higher temp with higher fan?

A lower temp would require more condenser which seems like it would require more energy.

A higher fan would obviously require more energy to spin the fans faster.

So which way is easier on the engine and gets me MPG numbers at least a little closer to the outside temperature number?

Any guesses?

prius04 · 07-26-2005, 12:20 AM

The condenser works by compressing the refrigerant. When that refrigerant later expands, it causes significant cooling. But it needs the fan also to move that cool air into the passenger compartment.

The fan alone works simply by moving air around.

Thus, the fan must use less energy, even if the fan is at maximum and the condenser at low. Compression takes a lot more work than just moving air around.

The AC will cool the car even if you are not in it. A fan will not lower the temperature in the car at all. It relys on the principle that moving air causes water to evaporate off your skin quicker than still air would. And that water pulls heat away as it evaporates. This is why a fan causes you to cool off some.

Thus, a fan is useless without a human with the ability to evaporate water off the skin. So don't leave your fans on when you go off to work. The electric motor actually adds heat to your house, and moving air does nothing for your couch.

Robert Taylor · 07-26-2005, 01:25 AM

Get the Huper Optik nano ceramic film installed for all windows but the front glass at a 35 rating. This will actually help reduce the heat load significantly.

I should have done it, but failed due to a snafu at the closest dealer, 100 miles away.

flareak · 07-26-2005, 04:11 AM

76

07-26-2005, 11:53 AM

I concur with flareak. I have it set at 76 and my mileage pretty much doesn't suffer because of it, relatively speaking of course.

**efusco** · 07-26-2005, 12:03 PM

I use Auto A/C usually set to 79 degrees. I get no complaints from a spouse that will complain if she's not comfortable. The kids seem to sweat a little in the back seat but without complaint and not badly.

I've been experimenting more with using 80 degrees on auto AC with the passenger side vents shut off when I'm driving alone and that seems pretty comfortable too. I doubt it makes a huge difference in mpg, but I'll take any fraction of a percentage on the 100+ degree days we've had the past week. I had a real struggle keeping my mileage up to my standard during the past week due to heat and AC use.

Note that in Auto setting when the car is hot the compressor and fan run hard to cool the cabin down, then automatically adjust both compressor work and fan speed to maintain the temp while minimizing the power drain. I think most people think it's effective in doing that though others have said the fan speed is too low and that back seat passengers tend to be too hot.

07-26-2005, 01:08 PM

79 in Missouri in the summer? Gaaaaah, I'm glad I'm not in that backseat.

shocker · 07-26-2005, 05:22 PM

I have the auto set for 76 as well and I haved been getting great mileage in heat.

prius04 · 07-26-2005, 05:59 PM

I think one of the keys to being comfortable with a highish AC setting is to have the blower aimed at your upper chest. This is the point that Evan made and I wanted to reinforce it. And if there is no passenger, then to turn off the vents on that side. Thus, with the outside temp at 90, you might be just fine with an AC setting at 80.

And if it's super hot out, aim at least one of the vents at your face.

However, if there are people in the back seat, there is no way to aim it into peoples faces. To make it comfortable for them I think you need to have the setting a bit lower.

But the higher the setting that you can tolerate, the better will be your energy use.

And since I was about 40 before I had my first car with a working AC, I have no problem with kids in the back seat enduring a higher setting. But not my in-laws.

EricGo · 07-26-2005, 06:24 PM

In my very low humidity southwestern climate, high speed fan works great with cabin set at 77 - 82 -- depending whether passengers are in the back of the car.

If I could aerate my back, I'd be even happier. Perhaps beads would help ?

07-25-2005, 11:49 PM	#1
natural_tools Member Join Date: Apr 2004 Location: Dallas, TX Posts: 30 My Car: 2004 Prius Package: #3 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Which AC setting do you think is best? Living in Dallas, there is no way to avoid using the air conditioner in the summer. So while I'm sweating in my black hybrid oven, I'm wondering... which AC setting is the best for MPG: low temp with low fan or higher temp with higher fan? A lower temp would require more condenser which seems like it would require more energy. A higher fan would obviously require more energy to spin the fans faster. So which way is easier on the engine and gets me MPG numbers at least a little closer to the outside temperature number? Any guesses?

07-26-2005, 11:53 AM	#5
Anonymous Guest Posts: n/a My Car: Package:	Re: Which AC setting do you think is best? I concur with flareak. I have it set at 76 and my mileage pretty much doesn't suffer because of it, relatively speaking of course.

07-26-2005, 12:03 PM	#6
efusco Troll Slayer Join Date: Nov 2003 Location: Nixa, MO Posts: 14,707 My Car: 2004 Prius Package: #9 Nominated 1 Time in 1 Post TOTM Awards: 0 Friends: 26	I use Auto A/C usually set to 79 degrees. I get no complaints from a spouse that will complain if she's not comfortable. The kids seem to sweat a little in the back seat but without complaint and not badly. I've been experimenting more with using 80 degrees on auto AC with the passenger side vents shut off when I'm driving alone and that seems pretty comfortable too. I doubt it makes a huge difference in mpg, but I'll take any fraction of a percentage on the 100+ degree days we've had the past week. I had a real struggle keeping my mileage up to my standard during the past week due to heat and AC use. Note that in Auto setting when the car is hot the compressor and fan run hard to cool the cabin down, then automatically adjust both compressor work and fan speed to maintain the temp while minimizing the power drain. I think most people think it's effective in doing that though others have said the fan speed is too low and that back seat passengers tend to be too hot. __________________ Evan E. Fusco, MD Seaside 04BC9/OEM EVb/NAV & auto-BT/XM Radio, CAN-View, Shark Fin, BT Stiff. Plate, Skid Plate & Strut Support

07-26-2005, 06:24 PM	#10
EricGo Three cats, one Prius, and assorted humans Join Date: Apr 2005 Location: Albuquerque, NM (SouthWest US) Posts: 1,810 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Re: Which AC setting do you think is best? In my very low humidity southwestern climate, high speed fan works great with cabin set at 77 - 82 -- depending whether passengers are in the back of the car. If I could aerate my back, I'd be even happier. Perhaps beads would help ?

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07-26-2005, 12:20 AM	#2
prius04 Join Date: Aug 2004 Location: NorthEast USA Posts: 1,155 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	The condenser works by compressing the refrigerant. When that refrigerant later expands, it causes significant cooling. But it needs the fan also to move that cool air into the passenger compartment. The fan alone works simply by moving air around. Thus, the fan must use less energy, even if the fan is at maximum and the condenser at low. Compression takes a lot more work than just moving air around. The AC will cool the car even if you are not in it. A fan will not lower the temperature in the car at all. It relys on the principle that moving air causes water to evaporate off your skin quicker than still air would. And that water pulls heat away as it evaporates. This is why a fan causes you to cool off some. Thus, a fan is useless without a human with the ability to evaporate water off the skin. So don't leave your fans on when you go off to work. The electric motor actually adds heat to your house, and moving air does nothing for your couch.

07-26-2005, 01:25 AM	#3
Robert Taylor Join Date: Oct 2004 Location: Rocket City Posts: 451 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Get the Huper Optik nano ceramic film installed for all windows but the front glass at a 35 rating. This will actually help reduce the heat load significantly. I should have done it, but failed due to a snafu at the closest dealer, 100 miles away.

07-26-2005, 04:11 AM	#4
flareak Senior Member Join Date: Mar 2004 Posts: 730 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	76

07-26-2005, 01:08 PM	#7
Anonymous Guest Posts: n/a My Car: Package:	79 in Missouri in the summer? Gaaaaah, I'm glad I'm not in that backseat.

07-26-2005, 05:22 PM	#8
shocker Member Join Date: Feb 2004 Location: Northeast Posts: 87 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	I have the auto set for 76 as well and I haved been getting great mileage in heat.

07-26-2005, 05:59 PM	#9
prius04 Join Date: Aug 2004 Location: NorthEast USA Posts: 1,155 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	I think one of the keys to being comfortable with a highish AC setting is to have the blower aimed at your upper chest. This is the point that Evan made and I wanted to reinforce it. And if there is no passenger, then to turn off the vents on that side. Thus, with the outside temp at 90, you might be just fine with an AC setting at 80. And if it's super hot out, aim at least one of the vents at your face. However, if there are people in the back seat, there is no way to aim it into peoples faces. To make it comfortable for them I think you need to have the setting a bit lower. But the higher the setting that you can tolerate, the better will be your energy use. And since I was about 40 before I had my first car with a working AC, I have no problem with kids in the back seat enduring a higher setting. But not my in-laws.