AC is automatically ON in AUTO climate control?

It means the compressor is ready if needed.

 

So if it's cold outside, I hit auto and keep it on 70 degrees, the AC light is on, but the compressor isn't on, just on standby?

 

That's correct. If it's needed to adjust the temp in the car, it'll come on.

 

Would that not still cause the compressor to operate and act as a dehumidifier?

 

I was just wondering this very same thing. I live in Wisconsin, and our morning temperatures have been as low as 16 F so far, and the idea that the AC was actually on (it's only a light, I know) really bothered me, so I'd always turn it off (I'm always on ECO mode).

Does having the AC on standby (Auto mode) affect mileage? Does MPG improve if the AC light is turned off?

 

If you want to know if the A/C is working in cold temps, just go listen under the hood to see if the compressor is running, it makes noise when on. It will only run down to certain temps, otherwise the system will ice up.

 

I noticed that when I set a temperature, switch on aircon, the thing goes to AUTO, but the fan goes up to high automatically and blow like crazy, so if it says 'Auto' does the fan then regulate once the temperature in the car drops?

Basically whenever it does that I immediately turn the fan down to a level I like, but more importantly to save power!

 

Yes, the fan speed will reduce. I usually turn it down right away too. I haven't actually used the automatic climate control nearly as much as I expected.

 

Funny I'm the opposite... I find AUTO reduces the fan speed too quickly for my tastes - particularly so in ECO mode - so I often turn it up manually at first and then press AUTO and let it dial it back down.

 

Yes, the compressor will run to dehumidify the air. Just assume the compressor is always on with the AC light lit unless outside air temp is "nearly" 32F.

From page 243 of the .PDF form of the manual:

■When the outside temperature falls to nearly 32°F (0°C)
The dehumidification function may not operate even when A/C is
pressed.

 

so would the consensus of the group be to leave the auto setting to have the AC come on or have the dealer change that option to not have the the AC come on...just the heat (I am in maine and more interested in heat most of the time rather than cooling )

 

I want to come back and correct myself, you're right. I must have previously been changing both the fan speed and mode, meaning neither one was still in AUTO. Realized this one day when I truly did change only the mode, and the fan speed went up. My bad

 

Interesting observations. You must live in the prairies to get that cold. ⛄There is no chance of it getting cold in my area however I wonder if anyone has had any experiences with their C in temps this cold. Anyone?

 

I’m still confused, and here’s why I know this is an old thread but it’s my understanding that the Prius accessory battery runs the AC unit but not the heat. In theory then, you could be stuck on a cold night and theoretically continue heating the cabin and not risk draining the 12 volt battery. The engine (if in ready mode) will continue to turn on the ICE to keep the HV battery charged as needed in heat only mode, but you could easily lose 12 volt charge running the AC?