Prius 4th Gen Heater

You can actually configure whether AC is switched on and off automatically by Auto in the head unit or with Techstream, FWIW.

 

That's good to know. Too bad it's not user configurable though. I suppose it's a "volatile" setting, ie: a battery disconnect would wipe it? I'm up on memory savers, but perdiodically want a truly comatose car, say for DIY brake work.

 

My Canadian 3rd gen will turn on the A/C light every time I select "Auto". It may or may not run the compressor. It will run it if I'm asking for cooling (set temp is lower than ambient by more than about 2 deg C). It will run the compressor as well when defrost is selected (it talks about this in the owners manual). It will not run the compressor if the set temp is more than 2 deg C higher than ambient. The two degree part is discussed in the owners manual, basically saying the operation is erratic when ambient is within 2 degrees of the set temp. Erratic as in not fully predictable whether you will get heating or cooling.

Remember, "Air Conditioning" is NOT "cooling", it's heating -AND- cooling -AND- filtering in Prius speak.

The part that often catches me is if I select "Front Defrost" I can't cancel it by turning the system "OFF". I have to actually press the "Front Defrost" button again to turn it off.

I suspect the gen IV is similar. It's a Toyota thing.

 

"In the head unit" means it is user configurable through vehicle setup.

 

The defaults for those are just the opposite on my 2017 Trim Two. It is interesting that the owner can change the outside air setting but not the AC one. Column 3 means TechStream.

 

I'm 99% sure that thing is wrong, too - I want to say that mine defaulted to that (but maybe I changed it with Techstream), and that I could change it through the head unit. I'll have to check...

 

Correct. I am not sure I have ever used the AC button.

 

Maybe from 2012 model year onwards? Again, my 2010 does not do this.

 

Yes.

 

So, contrary to the Owner's Manual, it is owner settable? Excellent.

 

I think there are actually 2 answers here, depending on whether you have a Prius or a Prius Prime. I believe the regular G4 Prius works pretty much as it has since at least G2. In the Prime however and since it works for extended periods (25 miles or so in NORMAL weather) it operates the Air Conditioner (Heat Pump) pretty much backwards. Picture you AC in when it is cooling the car. Low pressure coolant goes into the heat exchanger core inside the car and absorbs heat, it is pumped back out and the pumping further heats the coolant it then goes to another heat exchanger outside the car (usually in front of the engine's and/or inverter's radiators*) and heats up the outside air and cooling it back off. On the way back in it goes through a valve to reduce it's pressure making it ready once again to absorb heat from inside the car. All of that is like almost everyone else's AC works. (Most are driven by belts from the engine). In the Prime (and perhaps regular Prii) it is driven by an electric pump. Now what happens if you reverse this procedure? You heat the inside of the car and cool off the outside air. Now IF the engine is running, it will use the hot engine coolant to heat the car just like everyone is used to.

*I peeked under the hood, but without removing some decorative (top) and aero covers (bottom) I can't EZly determine what's what. I believe I did locate the electric heat pump behind the right bumper and under the right fender.


A "bit" more complex than that in your average car. This is just a schematic view. Alas I was unable to find an "in place" component view. I do have some pictures of the car with the front bumper (yes, all three parts) off. I will see if I find one or more that illuminate the situation.

 

At the center of the pic below you can see a hose coming out of what I believe to be the electric AC pump. I don't know what all the bits are, but you can also see a hose going into what I believe to be the radiator in front of the other two to cool the hot refrigerant that returned from inside the car.

 

The pic below is just a little further toward the center of the car from the previous pic.

 

The hot refrigerant comes from the pump - compress it to liquid, cool it, let it expand in the "other" rad. in the cabin, absorbing heat.
You would probably be correct in "heat pump" operation though.

 

get in the car, turn on the car, wait a few minutes or less, than manually turn the fan all the way up...heats and cools like a real car.

 

My car is real but a hybrid. I believe Prime and some other models have a heat pump so there is heat independent of coolant temperature.
I know my air conditioning can cool even in EV mode so my Hybrid is superior to a gas powered car.

 

Carista settings for Heater & A/C

Temperature dial calibration
-2°C / -1°C / *NORMAL* / +1°C / +2°C

Ambient temperature calibration
-3°C / -2°C / -1°C / *NORMAL* / +1°C / +2°C / +3°C

A/C ECO mode
*ENABLED* / DISABLED

Auto-increase blower speed when front defroster is on
*YES* / NO

Auto-turn on recirculate mode when A/C is on
*YES* / NO

Deactivate front defroster when AUTO button pressed
*YES* / NO

Open vents to outside air when ignition is turned off
*YES* / NO

Fan speed reaches its target…
SLOWLY / *NORMALLY* / FAST