Efficiency of increasing fan speed w/o lowering temperature setpoint

Altering the fan speed turns off the auto system, it also cancels the additional control imposed by ECO mode. If you wish to stay efficient, keep the car in ECO mode and just use the auto temp control. Set it where its comfortable, which might change depending on outside temps.

 

Looking strictly at energy usage, a higher fan speed will use less energy than a lower temp setting.

 

I think setting the AC to 78 is almost useless. As you state, you break a sweat. The AC is designed to blow cold air which should be in the low 70's or 60's which is where the ac would be most useful. Setting it at 78 i think it would hardly turn on. If the ambient temps outside require you to turn on the ac I might consider setting it to 72-75° to actually cool off the car.

There is a trade off you need to make:
1. Continue using the AC with a high temp setting and essentially waste energy because the car won't cool off.
2. Use the AC on auto with a lower comfortable setting.
2. Use the AC and turn it off when the car is cool and use the blower with a setting of low and no AC.
3. Only use the blower with a temp setting of low without AC.
4. Roll down the windows.

If it is hot outside I don't think it's worth saving energy if it means you are sweating in your car and driving uncomfortable. Just use the AC. I personally go with a blower only setting / roll the windows down a tad to let more outside air in. When it gets hot and the car is a sauna, you better believe the AC will be on. But that is fairly rare in SC. TX is another story but it depends on your comfort level.

I would also suggest that you close vents if you have no passengers. That way more airflow gets to your vents. If you feel your skin flapping and peeling back I think it's time to lower the blower setting just a tad

 

I am more concerned with keeping my HV battery cool than saving a few tenths of a mpg. I set mine to 72 and leave it in Auto. It does a good job of cooling the cabin down and keeping the HV battery temps under control in this 90F weather we are seeing now. In Texas you are seeing much higher temps than me !

With the variable speed AC compressor, as soon as the cabin gets close to setpoint the AC watts begins to drop rather quickly and once the cabin is cool the AC watts are greatly reduced. It does not take much cooling to keep the cabin cool. The system is very efficient.

I have found out by trial and error that the CC system's fuzzy logic is much smarter than my even fuzzier logic

 

Pretty well covered in the manual. When you change fan speed you are still using the temp set point but you disable things like auto control of the vents. What it does to the compressor control is an open question. I think its pretty safe to make a leap of faith that Toyota has engineered optimal efficiency into the auto system. Keep your car in ECO mode, HVAC in auto mode, and set the temp to where its comfortable. I usually try to turn off the A/C compressor while at a stoplight, which seems to help with the battery drain.

 

In ECO mode it reduces the output of the AC and takes "forever" to cool down the cabin. I prefer to not use ECO mode and cool the cabin down as quickly as possible. The quicker you cool the cabin to setpoint, the quicker the speed of the compressor is reduced and the AC watts reduced. You are also cooling the HV battery down quicker.

When the cabin temp is 110-120F in the afternoon after sitting in a parking lot at work all day, to heck with saving on mpg, I want to cool the car and myself down as quickly as possible

 

I have no problems keeping it cool in ECO mode, which lowers the compressor speed and fan speed. But I also have 20% tint all around.

Cooling down a hot car, 101:
1) Open the door and leave it open while you get ready to go.
2) Open the rear windows about 1-2". Turn OFF recirc mode and drive this way for about 2-3 min.
3) Put it back in recirc mode and roll the windows up again.

There's no difference between ECO mode and normal mode in terms of the target temp, the system will still try to get you to the target temp. ECO mode just does it more efficiently and takes a little bit longer. It doesn't take forever, it just seems that way when you're cooking.

 

I keep my AC at 70 and I dont really change it from there, I run in manual mode on it. The Auto mode is just too screwy and I dont like fresh air behind a bus or truck on the fwy.

 

You still get fresh air in recirc mode, just less of it. (20% compared to normal)

 

The set temperature is very different from the temperature of air coming out of the vents. When first turning on the A/C in a very hot car, a setting of 78° will produce air that is just as cool as a setting of 72°; it's just that as you reach a temperature of 78° in the cabin, the amount of cool air produced is reduced to maintain the cabin temperature. Even once it reaches 78°, the temperature at the vents will still be cool.

On the rare occasions I find it too hot to not have A/C, I usually have it set to 78°, or maybe 77° if the sun is on me.