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Discussion Starter · #1 ·
Greetings,
I try to run my heat without my compressor (AC light) to improve gas mileage. (Most of my trips are short at slow speed, so unless I'm on a highway I can only get in the high 30s MPG).

1. I know there MUST be a trick to turning on the heat with the compressor (AC light). Sometimes I click the vent icon (foot/front, etc) and speed (low to high) and the heat comes on without the compressor (AC light), but most of the time the compressor comes on automatically and I have to turn it off. What's the catch? Why does it only come on some times? Is there a certain temperature it needs not to turn the compressor (AC light) on?

2. To turn the heat off from the steering wheel, I have to hit the AC button twice. The first time the AC (compressor) goes on, the 2nd time it goes off.

3. The same happens with the front defroster. If I turn it on from the wheel (or climate console) and turn it off from the steering wheel, it turns on the AC (compressor) first. Again I have to press the button again, a 2nd time to turn it off. Isn't there an easier way?
 

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Well, I'll try. The A/C light is both for the A/C and Auto. Just pull up the climate screen and turn off the A/C, It has a bar underneath it. This will leave Auto control of the heat on but without the A/C. Now when you press defrost the Auto button will go off and when you press the defroster button again it'll turn on the Auto but without the A/C. Try it out.
 

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Effectively, the car has 3 main modes: heat only, auto, and off, unlike your home system that also has Cool only. In other words, there's no way to completely turn off the heat so thaty heat doesn't come on if the cabin temp is lower than the desired temp.

A/C in Toyota's climate control is deceiving, since they use AC and HVAC/climate control synonymously most of the time, except when directly talking about the refrigeration system.

As Drash said, in the climate screen, you can press the A/C button so that the yellow underline is dimmed, then the compressor is disabled, except possibly for front defog.

The button on the steering wheel is Auto, not AC. If you are out of Auto, then pressing once will turn HVAC off, then pressing again will turn HVAC back on but to Auto. When manually altering the vent duct used, or the fan speed, the HVAC comes out of Auto, though it will still try and maintain your temp setting as best as it can. You can turn off the HVAC completely with the OFF soft button on the climate screen.

The HVAC system is quite sophisticated. It has a continuously variable AC compressor, so it can alter the cooling rate as needed to maintain temp AND humidity. The system also has a cabin humidity sensor as well as a cabin temp sensor, so sometimes the compressor is run to dehumidify, instead of cooling. Of course it also has an outdoor ambient temp sensor also, which helps the HVAC determine how to set the heat, AC, fan speed, and duct choice. There is also a solar radiant heat sensor on the driver side of the dash near the windshield, so if the sun is strong, the car will make the cabin cooler so it will "feel" like the temp you selected. The system's design to achieve a "feels like" temp rather than an actual temp approaching your desired temp may be the reason Toyota didn't have a display for the current cabin temp.

Depending on how cold it is outside, operating heat can be just as hard on your MPG as AC during the summer. When not moving and not heating, the Prius will operate the ICE only to maintain SOC at about 2 bars, and not so much to maintain coolant temp. If the coolant temp falls too low, then you return back to the warmup cycle you normally go through when you start a trip.
When you heat however, then the car has to maintain a minimum coolant temp, so ICE may start simply to warm up the coolant. Also, sapping heat from the coolant for your own comfort also makes it take longer to achieve ideal coolant temp, let alone maintain it.
 

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Congratulations, and welcome to the club.

The following might be a bit sarcastic. Please laugh if it tickels you in the right place. :lol:

[sarcasm]
Welcome to the Prius family. Not in the history of modern automobiles has there been as well equipped or as efficient vehicle as our esteemed Prius. No company has ever gone so far as to develop such a fuel efficient vehicle, but on top of those strids they have provided luxury car features in a sub 30k vehicle. Nothing can compare.

Your vehicle is equipped with one of the most advanced and sophisticated cabin climate control systems available in any automobile. To take a line from the fameous inventor and telemarketer Ron Popiel, "Set it and forget it".
[/sarcasm]

But seriously, if the a/c switch light is on in the winter when you are heating, the system is not necessarily using the a/c compressor. In the true spirit of HVAC this system's goal is to most efficiently attain the setpoint temperature you ahve chosen, nothign more, nothing less.

More later...
 

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Discussion Starter · #5 ·
heat etc.

Bottom line:
1. Can you turn the heat on without having to shut off the A/C? If so, how?
 

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Re: heat etc.

drtravel47 said:
Bottom line:
1. Can you turn the heat on without having to shut off the A/C? If so, how?
Yes, just push the auto AC button on your steering wheel. Set the temperature to what you want, and then forget it. I leave mine that way year round.
 
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