Air conditioning system, Automatic mode

you're right.. he's an idiot.... auto does it all for you just like the manual reads. just set your temp and the car will take care of the compressor, fan speed, and recirculation.

 

For auto to control the AC, the AC needs to be on and you need to select the temperature you want. I find mine keeps the car cooler than most cars at a given temperature setting. A setting of 76-78 is usually about right in my Prius, other cars it's usually low 70s that feels right to me.

That temperature difference between my Prius and other cars is no big deal one way or the other, the Prius is just calibrated differently.

 

select "auto" then turn on the AC....then move the temp button, either up or down. depends on how hot or cold you want it. Once you have done this, the fan speed will adjust it's self to keep it at the set temperature.

Just hitting Auto does not automatically turn on the AC


It's a smart car, but it does not know if you want it hotter or colder then it is already.

 

i hope you guys know this car does have humidity sensors that automatically turn on the compressor when needed... it's like that for the genII and the genIII... if you hit defrost it turns on to help assist defrost...

did anyone read the original forums on auto climate control?

so... ac should not have to be selected.. and selecting a temp is well... a normal function... if you can't figure out a temp, use the windows.

 

A humidity sensor may turn the a/c compressor on to limit humidity in some conditions but it will not turn it on to limit temperature, that's the role of a thermostat.

My Prius works as described by xs650.

I assume that its an energy saving feature. If you press auto, the car will do the best it can to control temperature without running the a/c compressor.

If that's not cool enough for you, you press the a/c button to enable the compressor.

 

Remember too that even with the A/C button on, it will only run the compressor as necessary. I can see this with my SGII as it cycles once the car cools down and if outside air is cool enough, the compressor won't even come on, though it probably does if it needs to control humidity.

 

seriously though... it does both

they really didn't change the system much from genII to genIII

they did make the compressor electric instead of belt driven so it can ramp up and down it's speed when needed for cooling or humidity purposes.

there is no other way to cool the air... period... if the auto is on and there is cold air, the compressor is ON.... (and still in auto)...

what you guys are basically saying is that unless you turn on the compressor by hand, the air in the cab will not get cold.... that's crazy... it's an automatic system and i'm sure i've read a LOT more post on it than anyone here.

where's one of the other guru's that's not in torrence checking out toyota goodies?

 

Whenever the outdoor air is cooler than the air in the car, you can get cooling without the compressor. It may or may not be enough cooling.

Needing cooling for temperature control when its cool outside is quite common because of solar gain through the windows and body heat from the occupants.

The a/c switch doesn't turn the compressor on directly, it enables the automatic control system to turn it on it if its needed.

 

outside air... got it.. sounds normal to me

there is a light sensor on the dash for that solar problem.. it bumps up fan speed and such

you're not getting my point though... Auto mode is automatic... sure you can change setting but the whole system takes care of itself if you simply turn it on with the auto button and set your temp.

it ramps up and down the a/c on it's own...

How does the electric a/c compressor work?

read post 3... dan has been on there for a while.


A/C Compressor, Variable Speed with Supply Air Reheat?

firepa63 confirms it there... that pdf just provided voltage data and such, not function.

all i'm saying is that the OP does not have to press that a/c button... simply turn it on, and set temp....

 

When in "Auto" mode the A/C will never turn on unless the "A/C" button is lit up. When you push the "A/C" button the "Auto" button stays on because it is still automatically controlling the temperature. The "A/C" button allows you to choose whether or not you actually want the A/C to come on during the automatic temperature control. That's how it works in my car. With the "A/C" button off it just blows hot air forever. With both the "Auto" and "A/C" buttons on the temperature is controlled, and the fans ramp up and down with temperature.

 

Just to throw it out:

If the AC button is not pushed, ie: it's light is out, and then the Auto Button is pushed, will the Heating/Ventilating system's logic still use AC as needed, if the set temperature is low enough that AC would be needed to achieve it? I suspect that's the case but not sure:

It's something I've never understood. I do recall MSantos saying he's not figured out a way to keep AC off.

BTW: the Owners Manual uses the expression A/C exclusively, to describe any heating or ventilating function, further confusing things.

 

You have a Gen III, try it.:rockon:

 

Yes, the Gen 3 has an inverter driven variable speed compressor thats controlled based on a wide variety of inputs, just as Dan says.`

My understanding is that when you are in Auto, one of those inputs is whether a/c is enabled or not.

One thing that occurs to me is that one of the inputs that affect a/c in the Gen 3 is whether you are in ECO or not. My direct experience is with the car running in ECO mode. Perhaps yours is in a different mode. We know that the a/c runs differently to save more energy when you are in ECO. Maybe the effect of the a/c button is one of those differences. There would be some sense in designing it so that the compressor came on automatically when you are in normal mode but was locked out unless you enabled it when in ECO. I`ll run some tests once the wether warms back up.

The 2nd link is about the Gen 2 which has a different a/c system

 

But I am surprised to learned that the outside temperature sensor takes priorty over interior cabin temerature. In most cars, the outside temperature sensor just provides the reading of outside temerature and locks out the compressor when its near freezing. I am finding it very frustrating that when outside temperature is close to the temerature I set for inside, the A/C dosent work very effectively eventhough inside cabin temperature is way hot due to the solar effect. I have to manually set the temperature down a couple degrees to get cooler air, and triggering the fan into high speed. This is very strange, because in other cars that I own with climate control system, the temperature in A/C is pretty much set and forget. I usually get colder air and lower fan speed, rather than this not so cold air in higher speed in Prius. Or is there something wrong with my system?

 

It sounds like you're working hard to bend Auto mode to your will.
The only thing that Auto mode controls is where the air is directed and at what fan speed.
The temperature is always controlled by the temperature setting.
You know where you want the air and you know what fan speed you want. Just adjust them with their respective controls and you'll be happier (without Auto mode).
I never use Auto mode for this reason.

 

When I turn the system on with the Auto button, the A/C light comes on and the system switches to circulated air. Now does anyone remember if the system switches to circulated air when it's in the 40s or 50s outside?

 

For those interested to know. The mechanism which redirects the air inside vs. outside sits right on top of the cabin air filter. Check it out to see it in action.

- Remove the glove box
- Turn the car on.
- Switch the air on and toggle between recirc and outside air.

If you were brave enough, I suppose you could remove the assembly and see which wires power the mechanism specifically so you could disable it from switching. I'm not sure if that would affect any of your other AC functions or kick off some type of error (I don't see why it would).

 

I find this discussion interesting. The disagreements here are no doubt because different models behave differently.

When I first got my 2010 Prius, I felt that the AC did not work correctly when on "auto." It was full on, and froze the inside of the car, so I took it back to the dealer. They used a thermometer, and said it was working "normally."

Here's what happens:

On a hot day, if I turn on auto, the AC does NOT come on at all. The fans just ramp up automatically, faster and faster until maxed out, futilely trying to cool off the car to the set temp.

If I press both AC and auto, so both AC and auto are lit, the inside of the car becomes colder and colder, until everyone is solid frozen. It does not maintain the set temp, but goes into deep freeze storage cold.

The only solution I've found, it to turn on the AC, but set the temp very high. That adds heat to the freezing cold. But that wastes a lot of energy.

The other option is to keep turning AC on and off, on and off.

I wish it would just cool to the temp I've set.

Has anyone found a better solution? Is this something the dealer can fix?

At least we know the AC in the Prius works!

 

Here's what I do on a hot day: I set the temperature to 78 degrees, set the fan to a comfortable speed and press the AC button. I have no reason to believe that this wastes energy. The set point is roughly where I want the interior to be and the system seems to work well for me.
As I said before, if you know where you want the air and at what fan speed there's no reason to use Auto mode.