Prius A/C operating details

[fphinney]

How exactly does the Prius A/C system really work?

For instance, if you ask for a low speed fan A/C system to perform, does it's power demand start to lessen as the car's interior approaches target temperature? Also, I am quite sure that the compressor shuts off, once target temperature is achieved - - Right?

[seasalsa]

<div class='quotetop'>QUOTE(fphinney @ Sep 29 2006, 11:15 PM) [snapback]325944[/snapback]</div>

How exactly does the Prius A/C system really work?

For instance, if you ask for a low speed fan A/C system to perform, does it's power demand start to lessen as the car's interior approaches target temperature? Also, I am quite sure that the compressor shuts off, once target temperature is achieved - - Right?
[/b]

Maybe? Here is a great description of the Climate Control System by Tony Schaefer that I saved.

Prius air conditioning system
By TonyPSchaefer
Let me tell you that I was impressed with the Prius air conditioning system right off the bat. Working for a building controls engineering company, I immediately related with what the Prius was thinking. There are some differences in the details between building controls and car A/C systems, but the basics are pretty much the same.

Basically, it works like this: if the interior of the car is hot and you want it cold, the fan and compressors come on full-bore. On the other hand, if it's cool in the car and you want it slightly cooler, then they all come on slightly. As the temperature in the car reaches the desired setpoint, Prius recognises that it's getting closer and adjusts the compressor and fan accordingly. In that way, it eases into the proper temperature rather than running the fan all-out and then suddenly stopping (which is what most residential air conditioners do).

In an over-simplistic way of thinking of it, think of the fan speed as the proportional difference between SETPOINT and CUR-TEMP. For example:
SETPOINT=65º and CUR-TEMP=90º creates a high proportional difference resulting in a high fan speed.
SETPOINT=65º and CUR-TEMP=70º creates a lower proportional difference resulting in lower fan speed.
The Prius most likely recalculates several times per second (I'm guessing)

Secondly, you might notice that the vents blowing the air change. Rather than blowing a bunch of air out of the dashboard vents and straight into your face, Prius will adjust so the air is coming out of the windshield vents and at your feet. As the airflow rate decreases, Prius will reroute the air to the vents. This is very smart since the sensation of comfort is a combination of temperature and air movement. Doing this, Prius can keep you comfortable simply by moving air, chilling it a little less and using less energy.

Just like the variable transmission, you can think of the A/C as a variable system. Basically, if allowed to do it's thing without human interferance, it will work extremely efficiently.

[fphinney]

<div class='quotetop'>QUOTE(seasalsa @ Sep 30 2006, 08:00 AM) [snapback]325980[/snapback]</div>

Maybe? Here is a great description of the Climate Control System by Tony Schaefer that I saved.

Prius air conditioning system
By TonyPSchaefer
Let me tell you that I was impressed with the Prius air conditioning system right off the bat. Working for a building controls engineering company, I immediately related with what the Prius was thinking. There are some differences in the details between building controls and car A/C systems, but the basics are pretty much the same.

Basically, it works like this: if the interior of the car is hot and you want it cold, the fan and compressors come on full-bore. On the other hand, if it's cool in the car and you want it slightly cooler, then they all come on slightly. As the temperature in the car reaches the desired setpoint, Prius recognises that it's getting closer and adjusts the compressor and fan accordingly. In that way, it eases into the proper temperature rather than running the fan all-out and then suddenly stopping (which is what most residential air conditioners do).

In an over-simplistic way of thinking of it, think of the fan speed as the proportional difference between SETPOINT and CUR-TEMP. For example:
SETPOINT=65º and CUR-TEMP=90º creates a high proportional difference resulting in a high fan speed.
SETPOINT=65º and CUR-TEMP=70º creates a lower proportional difference resulting in lower fan speed.
The Prius most likely recalculates several times per second (I'm guessing)

Secondly, you might notice that the vents blowing the air change. Rather than blowing a bunch of air out of the dashboard vents and straight into your face, Prius will adjust so the air is coming out of the windshield vents and at your feet. As the airflow rate decreases, Prius will reroute the air to the vents. This is very smart since the sensation of comfort is a combination of temperature and air movement. Doing this, Prius can keep you comfortable simply by moving air, chilling it a little less and using less energy.

Just like the variable transmission, you can think of the A/C as a variable system. Basically, if allowed to do it's thing without human interferance, it will work extremely efficiently.
[/b]

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SeaSalsa -

WOW! Thanks, Great reply. I seem to have a little trouble getting satisfactory replies to questions & problems on this site. Other than that, this site is pleasantly unique.

The Prius never ceases to amaze me. I keep on finding out more & more fascinating details about this engineering marvel!

You made my day!

[Tideland Prius]

Not to mention that the Prius' A/C system is two-tiered.

This means that during the winter (which is when this system shines), your windows won't fog up. How? When you start the car and ask for heat, the system goes into recirculation mode and you see the recirc symbol on the dash. However, while the air directed to the feet is recirculated, the air directed to the face is fresh air which means that the interior can heat up faster because of the recirculation but your windows won't fog (or defog faster) because fresh air is being directed at the face level.

[ken1784]

Following is a good article by Denso engineer...
http://www.epa.gov/cppd/Presentations/Mats...%20inverter.pdf

Ken@Japan

[lisaann]

Hello,
I have a Prius 2006 and I am getting ready to buy a new one.
I have two Questions:
2008 or wait for 2009? any opinions?
Second question, has anyone had trouble with a mildew or mold smell from the AC vents when car is first started?
Thanks,
Lisa

[richard schumacher]

It kinda depends on why you're waiting. I'd expect that the '09 is essentially identical to the '08, except that it will cost more. And if it does have major changes, do you really want to buy one of the first ones?

Mildew can grow in the A/C in a damp climate. It helps a lot to periodically run the heater for a minute or two before shutting the car off, and to bring in outside air when the outside air is dry.

[la cucaracha]

Originally Posted by fphinney

<div class='quotetop'>QUOTE(seasalsa @ Sep 30 2006, 08:00 AM) [snapback]325980[/snapback]</div>

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SeaSalsa -

WOW! Thanks, Great reply. I seem to have a little trouble getting satisfactory replies to questions & problems on this site. Other than that, this site is pleasantly unique.

You did see the "I'm guessing" comment right?

[picstart]

The issue is forFlorida's highways the Prius 2007 A/C works for approx 90 mins then it cuts off . 30 mins later after driving with the windows down the AC will be back for another hour or more. This is by far the worst A/C we have ever had.

[Patrick Wong]

Originally Posted by picstart

...the Prius 2007 A/C works for approx 90 mins then it cuts off . 30 mins later after driving with the windows down the AC will be back for another hour or more. This is by far the worst A/C we have ever had.

I recommend that you have the car checked, to:

1. make sure that the refrigerant level is correct.
2. ensure the inverter coolant pump is operating.

The behavior that you described is not normal and should not be accepted.