A/C Auto versus non-auto

Auto will choose both the blower speed and the air outlet direction for you. In hot weather, the outlet direction is pretty much always going to be the dash outlets. It will run the fan speed up and down in response to the amount of cooling needed (and the variable speed compressor will tend to vary in speed as well, to keep up with the changing airflow).

That might well give you a bit more efficiency than you're experiencing without it.

What I find is that auto often chooses a lowish fan speed that will be perfectly comfortable in a driving position, but not move enough air for comfort when sleeping in back.

On the other hand, instead of cranking up the A/C further to solve that problem, another solution is just to take a little fan along, and set it up to blow the cool air from the front of the cabin over you in the back.

 

With "AUTO" you should reach a better efficiency:
It decides, which openings are the best (the lower ones for heating or the upper ones for cooling)
It controls the fan (more air flow, when you have a bigger difference to the target temperature/humidity).
It circulates the air, if there's s very big difference to the target temperature (mostly at the beginning to heat up/cool down). (So in summer you can support by opening all doors/windows a few minutes before driving to get the hot air out of the car.)
Of course it controls the air temperature by mixing with warm engine air, cool air from outside or (if needed) by switching on the electric A/C (when A/C is on).
If you switch off "A/C", change the vents and/or circulation mode, "AUTO" will disappear, but it will do it's best (but that's maybe not enough) to reach and hold the target temperature.

FP4 ?

 

i can't stand auto, it never gives me what i want. so i always use manual, but if i were sleeping in back, i don't think that would be comfortable because i'm always fiddling with fan speed and a/c on/off while driving.

 

If you're in AUTO mode, then manually change one factor, the others remain under automated control---which is interesting, and flexible, but potentially confusing. I normally like to let the computer chose air exit direction, but "fiddle with" temperature and fan speed myself, especially to prevent the initial fan (and compressor) speed from zooming crazy high. During steady-state cruise, the computer makes smarter choices of settings than most humans would.

There's one really wacky thing the AUTO mode does occasionally on mildly warm days when air conditioning is barely necessary to maintain tolerable temperature: If I pass through a shady area, or a cloud passes overhead, or I turn a corner so the sensor picks up cooler air from a different part of the interior, it will suddenly switch from air conditioning (compressor running near minimum speed), to heating---when I really, really do not want heat!

 

Does gen 3 have a dedicated air conditioning computer that doesn't seem my high limit switch or any of that would be bad because sometimes the thing will just come on I don't see any blockage no extreme pumping of the compressor and high pressure on the lower high side or anything like that everything's smooth I have not measured the high side pressure when it's stable and running just because I haven't but on low side it's just under 40 lb and the fat hose is cold then I'll come out to drive the car the next time turn it on and it won't come on it's really strange the lights are on in the car like it's

 

Right. The only "auto" trick that I usually switch off is the outlet selection. It distracts me if I'm driving in borderline weather and it vacillates between blowing the air on my feet or out the dash.

Everything else "auto" does is pretty much what I would do, so I let it. It makes sure not to blow the fan speed up before the core is warm in the winter, or the evaporator is cold in the summer, then it gradually sneaks the fan up once it can do some good. I like that. And it picks a fan speed and compressor speed just adequate for the amount of cooling wanted.

It doesn't alter my desired temperature setting. That's strictly an input; it's what "auto" will try to maintain for you.

 

I'm pretty much on the same page as Chap, although I have not noticed the vent switching in the Gen 2.

The only thing I have noticed is on longer trips the A/C will all of a sudden start pushing out colder air. I've never really figured out why that is, but I just click the temp up one or two clicks using the steering wheel buttons. I suspect that is has to do with the solar sensor acting in a clunky fashion although I can't really relate it to going in and out of sunshine.

Other than that I have no complaints about the way the auto settings work to manage the climate control.

 

My 09 almost blows icecicles. Wandaful setup . But then almost all my sanden sankyo denso radial compressor systems have been very cold.

 

I think all the Prius compressors are scroll designs—even the belt-driven one in Gen 1.