How to use the air conditioner w/o compromising fuel efficiency..Live in South Florida

Driving in ECO mode sets the A/C system to minimize energy use.

 

I would think a higher fan speed and not as cool a temperature would be more efficient than a slow fan with a cooler setting. Spinning the fan takes less energy than making cold air. Cycling the ac may be more efficient, but it may cause a problem with moisture within the system and the formation of mould. Hopefully this is less of a problem than with the earlier generations, but I don't know.

Another trick I use to increase efficiency is to turn off the ac going up mountain passes, and turn it up higher when coasting down the other side, when the energy is 'free'. Of course, this may not be so useful in Florida.

 

"and sometimes i will hit the AUTO button and maybe set it at 72 degrees. but that way the air conditioning compressor is running all the time, even though it is an electric compressor and not the conventional engine-driven type."

The AUTO setting does not mean that the compressor is running all the time. It will only run until the set temperature is reached, in your case 72 degrees.

I think stream's advice is the best.

 

The best bet is to run in Eco mode as Stream suggested, and set the temp for the highest you are comfortable with. The A/C compressor may indeed run constantly, but it will stabilize at a low speed, which is thus using low power.

If you are running manually, then setting the fan to a higher speed is indeed the most efficient thermodynamically, plus that added speed air aimed at your body will make the air "feel" colder, thus allowing you to set a higher temp.

The A/C is a relatively small load, so I would set it to a reasonable temperature and just enjoy the comfort and drive reasonably in Eco. There is no need to suffer for a few tenths MPG! You are also much better off using a fan in your house and raising the A/C temp there, than doing so in your Prius! (energy/planet wise)

 

You didn't state what color Prius you bought. White or Silver would be the best. Also get yourself a sunshade for the dash board and keep the security cover in the back deployed and covering the hatch area.

I find up here in the north during the hot months with a white Prius I can run around with the windows down and still be comfortable up to the low to mid eighties.

 

I thought when the Canucks start coming down in January the temperature drops into the 30's

 

+1 on ECO mode...and moderate your temp to keep the compressor from cycling as much.

Sometimes I just use the fan---but down here you HAVE to use A/C sometimes...

Best of Luck!

 

The compressor is the biggest load associated with the air conditioner. The ways you can reduce compressor run time:

1) Use the highest set point on the thermostat you are comfortable with.

2) Install tinting on your windows. Heat load from the glass affects your comfort and compressor run time. Good tinting will reduce radiant heat and sensible heat gain into the Prius.

3) Park your car in the shade.

4) Upon getting into your car - open the windows for a minute or so using natural ventilation to reduce the amount of heat within the Prius.

5) Use recirculation when first starting the a/c (the auto mode does this for you) and from time to time while driving. This reduces the amount of hot/moisture laden outside air that is being drawn into the Prius. Be careful not to keep the recirculation on too long; you need to ventilate the car to reduce VOC levels and CO2 levels inside the Prius.

However my recommendation is just enjoy your Prius and not worry too much about the a/c and gas mileage. You have one of the most fuel efficient cars ever built. It’s even more enjoyable when you are comfortable.

 

The A/C compressor in the Prius is a variable speed direct drive electrically powered unit. It only runs as fast as needed. By cycling the A/C on and off, you only manage to interfere with the control logic of the system. Put it on "Auto", set the temperature, and let it do its job.

If you want to minimize the mileage hit, use Eco mode and keep the temperature setting fairly high. However, it's important to remember that cabin air cools the HV battery. If you set the cabin temperature too high, you may save energy from air conditioning only to lose it to a hot battery.

Tom

 

I hate the Auto settings as it defaults to recirculate only. While I like fuel efficiency, I like fresh air even better.

 

Auto and Eco and recirc on all the time in Florida. Even in recirc there is always enough outside air for ventilation. Park in shade, use windshield sun screens, crack windows consistent with rain and security. Drive with all windows and moonroof open for several blocks or more with AC off, then close up and turn AC on. The AC load is enormous the first few minutes otherwise.

 

On hot days with Auto, It defaults to Recirc on automatically, but I override this at least until the car temp is below the outside temp, as this reduces load and cools faster. Once the car is below outside temp, then it makes sense to run recirc, or you are just wasting energy by blowing all the cool air out the back of the car. It will also never cool below 15-20 degrees below whatever it's source air is. In other words if you are sucking 100 degree outside air, your car will never be able to get below 80, no matter how long or hard the system runs. On recirc, the temp will keep dropping as the system inlet air temperature keeps falling.

 

I'm in Miami and I feel your pain. 82 degrees on November 29th kind of sucks. That is one of the reasons why I purchased my III with the solar package and installed the darkest possible tints. I usually keep the thermostat between 69-71 and the fan speed at 1 or 2 lines. This keeps my cabin at a comfortable temperature.

I'm averaging 50-51 MPGs and that's fine with me. I'm sure I can increase my average if I sacrifice some comfort but why? Like the others stated, enjoy your car.

 

Auto does not default to recirculation. It selects what it thinks is the best mode for the given circumstances. If you start with a very hot interior, Auto will select recirculation to maximize cooling. Once cooled, Auto will switch to outside air, unless the outside air is too humid and hot.

As pointed out above, even when set to recirculate, a significant amount of outside air is drawn into the car. There is a dealer settable option for complete recirculation, but most owners don't ask for it, unless they live in a very cold climate.

Tom

 

Re: "There is a dealer settable option for complete recirculation, but most owners don't ask for it, unless they live in a very cold climate."

Keeping the recirculation on in very cold climates can result in the inside of the windows fogging.

Here's what happens: When breathing occupants generate moisture which increases the indoor ambient air dewpoint conditions inside the car. When the window temperature drops to below the indoor ambient air dew point temperature condensation forms on the windows and the widows get fogged up.

Needless to say, reduced visiblity and/or wiping the inside of your windows while driving is not good. And a dealer that changes that ventilation option should understand the risks associated with fogged up windows.

The only way to reduce the dew point inside the car is to either use the ventilation that is already built into the air conditioning/heating system or open the windows.

My suggestion is to use the A/C ventilation which also heats the outside air prior to being distributed inside the car.

 

The key point missed is that the Prius uses the A/C compressor to dehumidify the air if needed. Even with total recirculation you will not get a moisture buildup inside the Prius if you allow the compressor to do its job. Obviously you can defeat it to allow moisture buildup and fogging, but you have to ask for it, in which case you get what you deserve.

Tom

 

Good point about the dehumidification.

A compressor properly operating = a cold evaporator coil (unless it's a heat pump, which doesn't apply here) which provides dehumidification.

However, during very cold weather , I would expect you'd be in the heating mode and the air conditioning compressor is not going to come on.

 

I've found that the dehumidifcation function does indeed work in the winter. I can watch the A/C compressor's current draw on my LCD. This is especially true in Defrost mode.