A/C comes on with AUTO... always?

The C has a button that can change the heat going to your feet, feet/defrost, or just defrost, there may be more selections not sure. anyway if I set it to defrost with the temp set to 68 it works well. I will shut it off to save the heat in the coolent because if the coolent goes to cool the engine will start and run burning fuel. when I want to defrost again I simply push the up arrow for the fan and the heater comes back on still in the defrost setting. otherwise the AC light is on and I don't want to have it on at all because the defrost works great without it. my morning commute is only 2.6 miles and it is tricky to keep my mpg up. if I use the front defrost button the fan comes on a high=loud setting and the AC light is on so I just use the fan button.

 

You can have the dealer disable the a/c setting when using auto at no cost...

 

Just to clarify, on 3rd gen prius hatchback there is a heat/defog mode, where the air goes 50/50 to the windshield and your feet. I just wish there was one more (without hitting the front defog button), that directed 100% of the air to windshield.

 

That one comes in handy when I'm on the highway and I want to defog the windshield without turning the HVAC on.

 

I have a Gen 3 hatchback and I bought it during the winter so I wasn't concerned with using the AC but now it's finally starting to warm up. If I leave it on auto will it use the AC when it thinks it needs to even though the AC light is off or do I need to turn the AC on for it to use it instead of just outside air?

SPH-L710 ?

 

If you have the Auto button on, the A/C light will be on and the compressor is in ready mode if needed.

 

The ac button has not been lit up since i bought it in Febuary and if kept it in auto on 70 since i bought it just yesterday i was warm and pushed the ac button which lit up and the air blowing in went from kinda tepid to nice and cool.

SPH-L710 ?

 

When I hit the Auto button, the A/C light automatically comes on and I have to tap it to turn it off.

 

Ditto for mine!


iPhone ?

 

Well, unfortunately that doesn't seem the case for me cause I use nothing but auto

SPH-L710 ?

 

What may be happening is that the car may be remembering your settings when shutting down. The next time you're going to shut it down, hit the A/C button so it's on, then shut the car down. The next time you power up, see if the A/C light is still on. If it is, then that's what's happening.

 

That's exactly what it does.
If the AC light is off, whatever mode you're in, the system will try to lower the temperature by blowing more air in, which leads to high fan speeds (less mpg ?) but the air being blown in will be at outside ambient temperature so there is a limit as to how much it can cool. To cool the air less than the ambient temperature, the light has to be on.

 

I know there's a little vent (grilled slots to the left of the Park button)) to detect the temperature/humidity inside the cabin, thus may have nothing to do with outside temperature directly on how the AC works. The AC amplifier uses something called Fuzzy Logic, which basically means it attempts to “think” more like human’s mind with more shades of grey and less black and white decisions. Included in this logic process is even an input to the AC amplifier regarding windshield wiper status, to aid in keeping fog off the windshield.

AC in AUTO mode, the speed of the fan also depend on the driving mode. If you are driving in ECO mode with AUTO climate control ON, switch to POWER mode, the fan speed will go up.

Saving fuel by setting the temperature higher hoping for the AC to work less may not be the best because we forget about the EXPENSIVE tracking battery that requires the proper cooling for long life services.

For those who feel better if the AC light is OFF, then do so but when the windows fog up just turn it ON until it clear then back to OFF as you like. In my previous car that use AC compressor with clutch, I realized that the AC ON light doesn't mean that the compressor is working (the clutch is NOT engaged), so I wired up the clutch switch and run the wires into the dash with the LED that only comes on when the clutch is engaged (AC is working). This way when I set my thermostat by the lever (old style with no digital number readout) once the temperature is cold enough, I can just move the lever until the AC clutch light is OFF, otherwise it would be just a guessing game because I can't really hear when the AC clutch is disengaged.

In winter, it is recommended that you run the AC about 10 minutes once a month to lubricate the compressor and the seals since the system works under permanent pressure.

Lastly, I can't figure out how the air RECIRCULATION works (in terms of when it turn itself off), the manual doesn't explain but says in some situations it will turn itself off. Unlike the old lever type that you can control it by cable to the flap yourself. I drive mostly in the city so I always turn the RECIRCULATION on so the exhausted fume/dust/pollens from the outside won't come in.

Side note, in another post several members suggest you always turn the RECIRCULATION on (to close the vent) if you usually park through the night in the area with rodent problems!!! A few had to spent hundreds of dollars repair the damages caused by the mice sneaking inside through the tiny openings of the vent.

 

FYI here is a list of the AC settings that can be changed by dealer (or with mini-VCI or other toyota aware OBD2) for the Gen 3 Prius. Most appear to be the same as on the v.

Air Conditioner
Display (Item) | Default | Content | Setting

Set Temperature Shift | Normal | Function to control with the shifted temperature against the displayed temperature. | +2 C, +1 C, Normal, -1 C or -2 C

Compressor Mode | Automatic | Function to automatically turn the A/C on by pressing the AUTO button when blower is on and the A/C is off. | Manual or Automatic

Air Inlet Mode | Automatic | Function to shift from INLET mode to RECIRCULATION mode when the A/C is turned on. | Manual or Automatic

Foot/DEF Auto Mode | ON | Function to automatically turn the airflow from FOOT/DEF on when AUTO mode is on. | OFF or ON

Foot/DEF Automatic Blow Up Function | ON | Function to automatically increase the blower level when the defroster is on. | OFF or ON

Ambient Temperature Shift | Normal | Function to control the shifted ambient temperature in relation to the displayed ambient temperature. | +3 C, +2 C, +1 C, Normal, -1 C, -2 C or -3 C

ECO MODE Cancel | OFF | Function to cancel the ECO mode drive when item is on. | OFF or ON

Noise and Vibration Reduction | OFF | Function to change speed of the compressor when item is on. | OFF or ON

From:
Gen III Prius - Customizable Parameters

 

You are correct, our 2011 Liftback does not turn on the AC when putting it in Auto Mode like it does on the V.. so, this behavior on our 2012 V was in fact different and takes a little getting used to. For now, we've been turning it off.. but didn't think it was actually running the AC. It's been way too cold here for that!!

So, kinda nice to know that this is normal, since we purchased the V used... & after reading this post, will probably opt to just leave well enough alone and let it do it's own thing.

Also, to comment on the AC.. we've never seen any 'mileage hit' on our Liftback.. (which has a SolarRoof) when using the AC... like we do when she's calling for heat.... our observations have been that we get the same MPG's with or without the AC on... it still blows cold while sitting parked.. (no engine running) so, must run off the big battery.. It will start the car up if the big battery is calling for charge.. We've maintained 56-58 MPG all summer long with our without the AC. Hopeful, the AC on the V will be similar in fashion..

Also, we found out by accident that the P.O. must have had the dealer remote start option installed. (I saw a post on Prius Chat somewhere explaining how it worked.. so, I tried it and it worked!!) That said.. since the V sits outside.. does anyone use it much? I assume I'll need to leave it in Auto for the heat to work? But do I have to leave the front & rear defrosters turned on too?

 

On mine and the previous Gen 3 hatch I had, the Auto mode retains whatever state the AC button was in, on or off, the last time you turned the climate control off. e.g. I turn the climate control on and select auto mode, if the AC is off and I turn it on, then turn the climate control off. The next time I turn the climate control to auto mode, the AC will be on (button lit).
IIRC AC doesn't function below 4 or 5 deg C to prevent icing damage to the condenser and even though the light is on, on the button, it doesn't mean the AC is operating.