Air conditioner always on?

[trapperjohn]

Hi,
If you have the climate control on lets say 73 degrees and the air conditioner has a green bar in the climate control screen, then when the inside of the car reaches 73 degrees will the air conditioner turn off or will the climate control mix in some heat to keep the temp while still having the air conditioner running?

Thanks,
Bryan

[aarons12]

it's not so much a matter of mixing in heat as it is shutting down the compressor (i think that's the right term) that cools the air until it's needed again. it would keep blowing 'plain air' at a low fan speed. if it got cool enough, it would switch over to heat.

[enerjazz]

I really would like to see some extensive details on the operation of the A/C. I've been curious if it's more efficient to set a comfortable operating temperature or to manually cycle the compressor as needed.

If the car is modulating the compressor to meet the temperature setpoint without introducing reheat, then that should be the most efficient.

If it's running the compressor for dehumidification, then reheating to temperature then that's less efficient.

The way everything else is optimized on this car I would suspect the program modulates the compressor, but I haven't seen anything to definitely confirm that.

[trapperjohn]

Hi,
Exactly my point but expressed better thanks.
So does the compressor shut off is the question?

Thanks,
Bryan

Originally posted by enerjazz
I really would like to see some extensive details on the operation of the A/C.   I've been curious if it's more efficient to set a comfortable operating temperature or to manually cycle the compressor as needed.

If the car is modulating the compressor to meet the temperature setpoint without introducing reheat, then that should be the most efficient.

If it's running the compressor for dehumidification, then reheating to temperature then that's less efficient.  

The way everything else is optimized on this car I would suspect the program modulates the compressor, but I haven't seen anything to definitely confirm that.

[aarons12]

i sort of pay attention to the temperature of the air coming out of the vents when i drive, and the compressor does seem to shut off. most newer cars have the compressor set to go on even at lower temperatures if it's humid, to keep the windows from fogging.

i would find it hard to believe that toyota didn't somehow optimize this in the prius considering how much thought they put into everything else.

[8AA]

I had read somewhere that the Prius air conditioning compressor actually has two speeds of operation. The low speed is used for general cooling, and the high speed is for max cooling. It's an improvement over conventional belt driven compressors and would seem to indicate that Toyota did provide the Prius with an adaptable environmental control system.

[DaveinOlyWA]

in a car, unless its not very warm outside, you will never maintain any kind of cool temperature so the compressor will run nearly all the time simply because the car is warm.

there are simply too many windows in a car. granted the glass has some uv rating to reduce heat absorption, but it aint nearly enough. (although not bad for clear glass it doesnt come close to a good tint job)

to test this thought. turn off the air conditioning and see how long it takes before it starts getting VERY warm. in most cases, the change will be immediate.

another thing to do is put the air on auto. then the fan will speed up and slow down depending on the set point and cabin temperature. realize that all thermostats will have a set range of a few degrees to prevent short power cycling intervals.

[Brian]

When ever my windows are up, then my A/C is on! But sometimes the weather is nice, so I put all the windows down and completely turn off the Air.

[HTMLSpinnr]

I had read somewhere that the Prius air conditioning compressor actually has two speeds of operation. The low speed is used for general cooling, and the high speed is for max cooling. It's an improvement over conventional belt driven compressors and would seem to indicate that Toyota did provide the Prius with an adaptable environmental control system.

It's actually variable speed - not just two. I have found, however, on MAX-COLD that it does step up to a speed which seems higher than it runs if I were to set it at 72°F on a 90°F day.

The A/C compressor is used for cooling and dehumidfying. The "A/C" selection in the climate control by default is "Auto", meaning if needed, it will run at whatever speed is necessary to control temp and humidity. It can be programmed to be "always on" when selected with a mini-scanner, but I don't see the point in doing so.

There's alot of fuzzy logic going on in the climate control computer to ensure that passengers feel the set temp - which includes humidity control.

The A/C computer also controls when to use the recirculate function. When Max or high cooling is needed, it will use recirculate to get the cabin cooled more quickly. If mild cooling is needed, the recirculate feature will turn off. At this point, it runs in a split recirculate/fresh air mode (like the '01-'03 Prius) where air at the bottom of the cabin is recirculated (since cooler air "sinks") and fresh air from outside is drawn in and cooled as well.

The New Car Features guide goes into great detail on how the A/C system works. For $10/day, anyone (in the US) can download it in PDF form from techinfo.toyota.com. I learned alot from it. There's alot more in there than I can reasonably type here.

[8AA]

Thanks for the information Rick. Just when I'm totally impressed with the features of the car, I find out there's even more to love about it. It's a lot like an infomercial... "Now how much would you pay for this car? But wait, there's more!"