Impossible to have climate control set to ONLY not exceed a temperature, right?

That would make too much sense... Life is all about being too hot or too cold, not just right. Goldilocks and the three bears is fake news!

 

Thats Auto mode

 

Yeah, I've camped in my Prius many times even at temps as low as 15 degrees fahrenheit but I've never left the car on overnight. Instead I wake up and turn the car and heater on for 15 minutes. And when in a hot place that heats up first thing in the morning, that's my alarm clock to wake up and start driving more.

 

Turn it off auto and press ac

 

I can't think of a way to do this with the controls provided.

The easiest hack I can think of would be to spoof the interior temp sensor. Assuming it's some kind of thermistor, add a cut-out switch and put a fixed value resistance equivalent to 70°F on that line so that the car thinks there's no HVAC work to do.

Once the sun hits the sensor on the dash, it'll add some cooling and that might get you to when you'd wake up normally. Then you would throw the switch to go back to full auto.

 

That should do it. So simple.

 

That's what I'd try doing. If it's in AC with the temp set to 70 and NOT in auto, I would expect it to not run in heat mode. But that's impossible for me to test in this location at this time of year since our morning lows are usually about 80º and it refuses to go under 75º.

 

Maybe ours is different, but if I did that in our car, the air conditioner would run continuously at the set level, rather than only when needed as controlled by the thermostat.

This would certainly allow the car to get quite cool overnight, but it would use more energy and run the engine more.

I think the real goal is "run the engine as little as possible" and not "prevent the heater from running"

 

The thermostat works with auto on or off. Realize that the air coming out of the vents will usually be significantly cooler until it mixes. The car also factors in solar radiation during the day.

 

Then it's worthy of an experiment to see if that runs the engine "less enough."

 

Agreed! We can kick around ideas all day, but you don't know for sure till you try it. Our low this morning was 81 and it's 86 in the garage, so not much chance of experimentation here.

 

Another reason to develop your skills and tricks for manually controlling the weather inside your Prius so well you can do it in your sleep.

 

Well that's exactly what needs to be tested. I was thinking about it too- my old Subaru would pass this test. It had full auto climate control, but if you hit the mode button then the mode is the only component that would not be automatic. Likewise if you had been in auto and pressed the fan speed + button, then the fan speed would go up one notch and stay there forever, but the mode would still be automatic.

In other words there is such a thing as semi-automatic on that car, and there's no reason that a Prius system couldn't work the same way.