Auto-AC Button on Steering Wheel

[anti-gas]

Ok, now I am hoping that someone has the correct answers to this.

I noticed on my 2008 Prius, there is a button on the steering wheel that says, "Auto A/C". When I press this, the AC system comes on full bore. As I continue to drive, nothing changes. The owners manual says very little about this feature, what it is supposed to do and how it is supposed to work. What I want to know is the purpose of this button, and how it works and or what is it really supposed to do. My dealer can't tell me squat about it other than that is the Auto A/C function. If I push the button again, it shuts the system off.

My thought was, that this would turn on the A/C system, and as the temperature drops in the car closer to your set point, it would reduce the fan speed, but that is my best guess and it clearly does not do that.

My next question is if you set your A/C temperature control to 70 degrees vs. LO "lowest setting", do you save fuel at the 70 degree mark because the compressor works like a home A/C thermostat which shuts the compressor off when the temp reaches 70 and then back on if it goes above 70? Of by keeping it on 70, does the system turn the heat on to bring the temp, up so its not too cold in the car. From my preliminary tests, it seems to save me fuel consumption in the 70 degree mode, rather than the Lo mode. I want to be sure of this before I continue to operate in this fashion. I'm looking for that happy medium between comfort and fuel economy. I want to squeeze out every last penny from a gallon of petro.

Thanks all.

[abq sfr]

The Auto-AC button should have really been named "Climate Control." You set a temp for it to maintain, and it uses the AC or Heat to get it to that temp, and it will act on high humidity conditions too. I worried about that too and almost drove myself nuts when I first got the car, dinking around with the individual settings. Now I simply dial in a temp and let the car worry about it and it works great. Yes, the more conservative you are with its use, the more mpg you will get. In the summer I usually set Auto to 80 around town, it keeps me and my wife comfy even if its high 90s outside. In FL I dont think you have a real winter. Basically the heat takes heat from the engine, which costs gas to bring back up. Also, initially I think there are some heating elements that take voltage from the traction battery before the gas engine is warmed up.

[Rest]

Originally Posted by anti-gas

as the temperature drops in the car closer to your set point, it would reduce the fan speed, but that is my best guess and it clearly does not do that.

Mine does this.

[V8Cobrakid]

70 is a little low for some of the cars out there. it's a defect of sorts... or so it seems so far. never recalled or anything on here.

so.. there are a few on here. like me. who keep it around 80 in the mid summer to keep the battery from draining. others (seems to be the majority) say that they have no problem when it's about 100 out... set at 70 or less... so.. defect?

If you have someone that you can compare to, or many... you may be able to get a dealer to lean your direction. never being rude, of course.

[Fraser]

Set the AC with the Climate window on the MFD. Then, whenever you want to enable or disable it, you have the option of pressing the Auto/AC button on the wheel. As your set temperature approaches the outside temperature, the fan slows down. If the set temperature is higher than the outside temperature, the produced airflow becomes warmer.

[V8Cobrakid]

btw.. there is a sensor on the dash. if light is pointing in through the windshield, the fans are turned up.

[KMO]

Originally Posted by anti-gas

My thought was, that this would turn on the A/C system, and as the temperature drops in the car closer to your set point, it would reduce the fan speed, but that is my best guess and it clearly does not do that.

It does, as long as there is a set temperature. It doesn't if you set "MAX COLD" or "MAX HOT".

Also, after selecting AUTO, you can override the fan speed or vent flows on the touchscreen, and you go into a "partial auto" mode - other functions remain on automatic, except for what you manually selected. Reselecting AUTO puts everything back to automatic. So if you touch a fan speed control after selecting AUTO, it won't change the fan speed.

[lefat1]

i live in the same area as op, set mine at 76 and it does the rest all from the buttons on the steering wheel

[anti-gas]

I will try it again today. I have always had the A/C system set to 70 degrees then pushed the auto button, but after an hour long drive, the car got nice and cool, but the fan speed never seemed to change at all, still blowing full bore.

I have noticed that when I play with this feature, it somehow changes my Recirculate air setting to the fresh air setting letting in other car exhaust and humidity from outside.

If I were to keep it on the 80 degree temperature and then use the auto feature, would it ever turn the heat on? How does it regulate tempurature, does it only cycle the compressor on/off or does it do something else to make it artificially warmer if the temp drops to far?

Looking for the coolest temp in the car without using too much energy. Trying to find that happy medium. Thanks.

[qbee42]

To answer your second question, the A/C compressor on the Prius is even smarter than your one at home. Rather than using a simple on/off thermostat (bang-bang control), the Prius uses a proportional system. It runs the compressor faster if it needs more cooling, slower if it needs less.

As for temperature setpoint, don't worry too much about what the numbers say. Depending on the sun and how I am dressed, and whether I need heat or cooling, some days I am fine with 78, other days I set it on 68. Use the temperature buttons on the steering wheel as comfort and fan adjusters: if you need it cooler drop the temperature a few clicks. It's that simple.

Tom