2010 Prius II: A/C on for Defrost?

Yes.

Because people such as yourself don't understand that "defrost" means "dehumidify" and that only the AC can dehumidify.

Toyota lawyers, ever the nannies of the world, want to prevent lawsuits that result from stupid people driving around with their windows fogged up and then claiming they caused some horrible accident because the car didn't read their minds and do what was needed instead of what they told it to do.

So they program the car to do what's needed--and, to prevent phone calls, they specifically tell it not to light the AC light.

At least they don't do as recent Hondas do and carry over the A/C function to any subsequently selected environmental setting, even in dead of winter.

Wrong again, troll-breath! Heat will also dehumidify, as will slightly drier air at the exact same temp as the inside air. I want to make sure I can keep the windshield clear without either freezing my feet with the Floor/Defrost setting, or being unable to briefly switch to Recirculate when a diesel truck gets in front of me when I'm in that stupid 'Front Defrost' mode. Toyota has made this an impossible dream. On every previous car I've owned since 1986, including our Camry, one could set the airflow to "Defrost" and still be able to activate - briefly, to prevent re-fogging - the recirculate setting.

So instead, they're going to cause accidents by making people look down and repeatedly punch buttons until they can shut off the outside air intake in heavy traffic. *Great* strategy.

I hope that you are, once again, wrong.

Any Toyota techs here who can give me a polite, informative answer?

I believe that I may be insufficiently grateful...

Heat will turn the moisture from liquid to vapor; it will not remove the moisture, as the AC system will, troll-breath.

Think about it: in the summer, when it's damp and you want to remove the moisture, you don't want to turn on the heater. There's a reason for that, troll-breath.

The next time it's 70 degrees and damp and you see cars go by with ALL the windows fogged up, now you'll know why they're doing it wrong.

Then you don't get it. You think that the purpose of air conditioning is to cool the air. No, that's the purpose of refrigeration--and that's for storing meat.

Humans with their body heat and sweat mechanisms and their breath exuding moisture need to dehumidify the closed environment in order to stay cool.

You don't get it that the car's system is not like your house system; it runs both the AC and the heating system simultaneously to keep the temperature you want. The AC dries the air to keep you comfortable and to reduce interior moisture buildup, and then the heater warms it (if necessary) to keep you from freezing.

You're saying you can't do that now on some car you now own?

My 07 Prius lets me do just what you said. They even have a button on the steering wheel for recirculate. It's a law in Japan that the recirc button be readily at hand, just like it's a law in the US that the defrost button be readily at hand.

Ah, the mark of one who doesn't like the answer so he calls the messenger names and then goes shopping for an answer he likes.

Yes. You really don't understand "relative humidity"? Do you believe that you need A/C to defog your windshield when it's 40 F outside? No, you simply warm the air passing through the ventilation system; this lowers the relative humidity of said air, drying it. If the air outside the car is lower in moisture than the air inside (and this is often the case) then you simply need to blow it over the windshield to defog it. Do you honestly believe that in countries where automotive A/C is not a common option that they can't defog their windshields...?

I miss having a Volvo for one reason: the people in alt.autos.volvo tend to understand both cars and physics.

No, the moisture is removed as it exits the car with the air, through that rear vent you probably don't even know exists. Further, as air gets warmer, the relative humidity decreases. If you can stand the ever-increasing temperature in the car, you can defog with heat even with the recirculate on. It works much better, though, to just exhaust the heated air and take in fresh air to heat and defog, when possible.

Other people's mistakes aren't at issue here. *My* windows don't all fog over.

I understand dehumidification through condensation at the evaporator coils. You don't seem to understand using dryer air at more or less the same temp to defog.

(...) > could set the airflow to "Defrost" and still be able to activate -

The 2010 Prius has the recirculate button, but it will not operate when the car is in front defog mode. Since you didn't know even that much, you don't belong in this conversation.

I was looking for a "yes" or "no", not a brawl with a troll who isn't even familiar with the vehicle in question. Further responses from you will be ignored.

Au contraire. Other people's mistakes are the center of the issue here--that's why Toyota has a stellar legal team that they pay a bunch of money to.

You don't understand "dew point", and you conveniently ignored your bullshit being called out when you claimed that having the AC on meant you were being "freezed out" when that's not the case at all.