A/C and Heater

The compressor is powered from the inverter, via the traction battery (the traction battery is a 200V device and the system uses about 350V, which the inverter produces). The compressor is a variable speed device, and that is used to "control" the cooling rate, along with the fan speed.
I hardly ever use A/C cooling so I can't answer if the temp delta will affect the cooling rate, but I suspect it will in that the compressor will run faster and the fan speed will bump up (using "Auto").

 

Set in auto mode and set your desired temperature. Adjust as required. Just remember this is also what keeps your traction battery cool. Over heating is hard on packs! H

 

Is this because of the vent on the back seat? I never thought of that (I'm a new Prius owner)...

 

Yes, the traction battery gets its' cooling air from the cabin via the vent beside the rear seat. It exhausts the air just behind the rear wheel on the right side of the car.

 

Regarding the second bullet:

Do you mean to say: When it's hotter out does the AC get colder to compensate? To answer that I'd say:

The AC works at full efficiency whenever it's running. It runs when the cabin temperature is above what you've set, shuts off when they match. To improve cooling it, say when there's a big difference between cabin temperature and what you've set, it plays with the fan speed (assuming you've got the ventilation system on Auto, where it control fan speed as needed). The more the difference, the faster it runs the fan.

Regarding the third bullet:

There is no separate pool of "cold air". Air comes into the cabin through the ventilation system as usual, it runs through both the heating radiator and the AC radiator. If it's hotter than the cabin temperature you've set, then the AC is turned on, ie the compressor starts to run, which in turn chills the AC radiator. If there's a big difference between outside and set temperature, it runs the fan faster.

In a situation where there's cabin air temperature you've set is the same or higher than outside, the AC compressor will continue to run (chilling the AC radiator), and the regular heating radiator will also work, heating up with coolant brought in the from the engine cooling circuit. First the AC radiator cools the incoming air (and dehumidifies it), and then the heating radiator warms it back up. This is the situation when you use the AC on cool rainy days, for example. Basically to stop the windows fogging up.

 

No, the Prius system will shut off the AC compressor if the system needs to heat the air. And it's a variable speed compressor. If you have the defrost turned on it will run the AC compressor even if heat is called for. This is to dehumidify the air.

 

The A/C control is quite a bit more complicated than cycling the compressor off and on. The ECU watches several temperature sensors as well as the temperature setting. The compressor is, as noted above, variable speed, and the ECU determines the most efficient speed to do what you have asked it to do. From my interpretation, the temperature setting will have a effect on the system operation as you change the difference between the setting and the current ambient in the car.

 

I've done HV battery temperature sensor readings with Enginelink app in both recirc and fresh air modes and the battery definitely stays cooler with fresh air. Recirc doesn't allow sufficient flow through.

 

Worth noting here is that the compressor's effort is always automatic, controlled by the temperature setting. What this means is that it's more efficient to set the temperature to a comfortable temperature for you than it would be to set the temperature to something very low and adjust the fan speed manually to stay comfortable. In the latter case, if you have the temperature very low and the fan running slowly, then the compressor is working really hard to cool the air, but not much of it is going through the system; it's wasting a lot of energy trying to cool air that's not there.

So just set it to whatever temperature makes you happy, and let Auto do its job whenever possible.

 

I have a similar question and will add it to this thread. This morning it was 50 degrees F. I have a 2014 Prius plug in advanced. I leave it in auto climate all the time. I had it set at 70 from my drive home yesterday as the outside temp was 80. The ICE started and heat began coming out of the vents. I noticed that even though the heat was on the AC light remained lit. It did not seem humid to me in the cabin.

Does the AC light indicate that the AC is running or that it is available to run if needed to reduce humidity?


iPhone ?

 

On ours, I'm pretty sure the AC only runs when you've pushed it's button, turned it on, and it'll show lit to confirm this. I wasn't clear about this when we got the car, thought that AUTO might run AC when warranted, even without the AC button being pushed. But I don't think that's the case: AC does not run until you've pushed it's button, and the light's on. The only exception being when you push the front defog button: then it force-runs AC, and shows a light on the AC button.

You can tell by the feel of the air I think, AC treated air has that dried/chilled feel, even if it's reheated.

 

You are probably correct Mendel, but why do they call it auto? Guess I had better do some reading. H

 

No, the system if operated in "Auto" will heat or cool as necessary to keep the cabin at the set temperature. The A/C light will be on when in "Auto", but the compressor will not necessarily be running. Note that if you are in the sun (shining on you through the windows) it may feel hotter than the set temp. You can lower the set temp to compensate. The car will compensate if the sun is shining on the dash, where one of the sensors is located.

Unlike many old technology cars, the A/C system doesn't rob the car of a lot of power (or fuel efficiency), though it does use some (no free lunch).

There are quirks to the system as well. For example, if you just want to run the fan and turn it on using the fan button on the far right (where mine is) it will usually turn on the A/C light. Just turn it off if you want it off. Next time you turn on the fan, if you haven't used the system in "Auto" since last using the fan, the A/C light will remain off.

Because here in the "cold white north" we don't need the A/C cooling function often, I can usually "get away" with just the fan. But I do use "Auto" on "hot" sunny days, particularly if I'm going to be driving for more than a few minutes. "Hot", for us, is 25 C and up, usually below 30C. I also use it when I'm busy driving and don't want to mess with controls - as in lazy.

 

Thanks for clarifying that. I use auto climate because I am spoiled. My 2005 rav4 had me as the climate master control program for nearly 10 years. I am turning that role over to the computer, which thus far is doing a great job!


iPhone ?

 

I could be wrong, but in my experience, if you turn Auto on, it turns the AC on. You can then turn the AC off and the system will maintain the set temp as long as the outside temp is less than the setting. Once the outside temp gets much above the set temp, it will not turn the AC on to cool things. On the trip we're on, I didn't use the AC until we got out of Montana because the outside temps were in the 50's and 60's. Once we hit North Dakota, things started heating up and the AC was needed to keep the cabin at 72-74.

Turning on the defroster also turns on the AC, but you can then turn it off if you don't need the air dehumidified to keep the windshield clear.

I don't know if I'd lose any mpg by leaving the AC on, but I don't like dry air if it's not needed to keep things cool. Some will suggest leaving it on all the time for the battery, but air in Phoenix is already dry, so it the cabin is 72-74 where I keep it, I don't see the need to run the AC. Then too, some will suggest always using the recirculate setting. I believe using Auto switches the recirculate setting as needed and there is always a certain amount of outside air being brought it regardless of the setting.

 

If I've got AC off, no light showing on its button, and I hit auto, I never see the AC light come on. And from the feel of the air, there's no "stealth" AC at work.

And this is just the way I like it. Not sure why, with others reporting AC coming on with Auto use, but I'm not complaining, this behaviour is my preference.

With our previous vehicle hitting auto invariably triggered AC, and don't think that was my intention ONCE, in all the time we had the vehicle.

 

Coincidentally I just read an interesting section in my Prius manual about this. Just got a 2014 Prius a month ago and am reading through the booklets. This might explain something of what is going on... on pg 208 this is what the manual says about using the AC

"Eco drive mode controls the heating/cooling operations and fan speed of the air conditioning system to enhance fuel efficiency. To improve air conditioning performance, adjust the fan speed or turn off Eco drive mode."

I find this really interesting. Either you get good gas mileage and decent AC by staying in Eco mode (and I assume put strain on the hybrid battery) or turn off Eco mode and get great AC, but sacrifice MPGs. This doesn't seem like the most efficient way to deal with this, but I'm no engineer so I figure Toyota must have had some logic behind this.

 

I do notice that the interior fan will not spin as fast when in ECO mode. Presuambly this also works for AC: it will probably cool less (and therefore consume less energy) when in ECO mode.
But this has nothing to do with the hybrid battery. The ECO mode spoken of is the ECO and Power buttons that (otherwise) only remap the throttle. It is not the EV button that you seem to be thinking of (because ECO mode as such will not put extra strain on the hybrid battery).