Air conditioning reviewed

Air conditioning, as a term, has been used by the auto industry for years to refer to the refirgeration of air. However the truth is that in most other parts of the world, and amongst those to do building HVAC for a living, air conditioning is both heating and cooling of air, along with air filtering and humidity control. True air conditioning indicates a fully controlled air environment.

Toyota's use of the term Air Conditioning in the Prius is technically correct, but many drivers confuse Toyota's use of the term with the common belief that Air Conditioning refers only to the cooling of cabin air.

The light on the dash indicates Auto A/C. If that light is on, the system will make all the decisions about air volume, air output, air source, compressor status and heat status based upon the temperature setpoint that is changed either at the steering wheel or on the MFD. The Prius system is fully automatic and behaves the same as nearly every other automatic climate control system I have ever used.

Now, with the light on, if you go into the MFD and start adjusting the system, the Auto A/C light will go off. That means that the system is not fully automatic anymore. Starting at Auto A/C, as soon as you manually adjust the fan speed, the system will not be able to adjust the fan speed automatically. That is why the Auto A/C light goes off. Not because the system is not going to run the A/C compressor, but because it is not fully automatic anymore. The same goes for air output, if you manually adjust that from the Auto A/C light, the system will not be able to choose the air output.

The temp setting does as it indicates. Its goal is to keep your cabin at the temp you indicate. It will heat as necessary and use the compressor as necessary to achieve these goals.

There is an A/C button on the MFD in the upper left corner. I call that the A/C defeat switch. If the yellow bar at the top of that soft button is on, it means that the automatic system has access to the A/C compressor. If you press the A/C button and the light goes out it means you have told the system that it may not use the A/C compressor. This light does not indicate when the vehicle is using the A/C compressor. You have no direct control over when or how the system uses the A/C compressor. You can adjust the cabin temp up or down, but that is the only control you have aside from the A/C defeat switch. I cannot stress this enough, use your A/C or loose it. The health of an A/C system is based upon it being used. Compressed refrigerant, as it goes through the system, carries with it refrigeration oil, which is mostly used to lubricate the compressor, but also keeps the o-rings and seals fresh and soft. If you intentionally choose to not use the A/C you are choosing to let the system dry out and that will require future expense to bring it alive again. The Prius battery also requires a "room temperature" environment for most efficient operation. If the interior of your cabin is hot after sitting out in the sun, the Prius uses the climate control system to bring the cabin temp down to a level which helps the battery operate efficiently. The battery does not run efficiently above 100 degrees and doesn't do that well when it is freezing out, so a plesant cabin temp is also plesant for the battery.

So, what I'm saying is that you should never defeat the A/C system as it does more than just keep you comfortable.

Additionally, the compressor is not on or off, as in most cars, but is variable speed and runs at speeds necessary to provide the appropriate amount of cooling to the system. In the summer, as the cabin cools down the compressor will slow down. This is a significantly more efficient A/C design than in conventional vehicles in which the A/C compressor is engaged or not engaged and nothing in between. You should also be aware that the A/C compressor is electric and as such does not load down the engine with a high demand pully accessory. Instead all of the energy used to run the compressor comes from the HV battery and electrical system.

I have discovered that I loose only a couple of MPG in the summer with the A/C, if that much. As such I do not consider it a sufficient loss in MPG to choose to go without A/C. And considering the additional benefits of running the A/C (ciruclation of oils, battery cooling), there is no question that the auto A/C system that Toyota put on the Prius is there for a reason and is as integrated into the vehicle's operations as the HSD system.

 

<div class='quotetop'>QUOTE(jeromep @ Jul 27 2006, 02:14 PM) [snapback]293305[/snapback]</div>

Wonderful post.... Thanks.

 

Bob, thanks for asking the question I've been meaning to ask, and jeromep, thanks for that very informative and lucid answer!

 

seldom use the A/C, maybe a few times a summer, never gets really hot enough, never use it on Auto. Only time I use it is in the winter and have the system on the windshield setting to clear the moisture off the window. Almost 3 years old and no problems. The way I use it on all my vehicles some for over 10 years. Once a month for 4 minutes is enought to circulate the oil in the system. Current Prius pump is even better in that respect as there is no input shaft seal to "dry out" most of which are carbon seals any way.

 

The Prius's A/C is, perhaps, the best I've encountered. It's so efficient that I find myself turning it down. B)

 

<div class='quotetop'>QUOTE(jeromep @ Jul 27 2006, 01:14 PM) [snapback]293305[/snapback]</div>

hi jerome. i just happen to run across your article on air conditioning and i enjoyed it very much. you explained things very well. you answered things expertly. i think your article will help anyone who reads it. pete

 

<div class='quotetop'>QUOTE(jeromep @ Jul 27 2006, 03:14 PM) [snapback]293305[/snapback]</div>

In a home AC system the chilled line is insulated. Why isn't that the case for a cars? I note that the chilled line runs down close to the oil filter, turns up and runs up and into the cabin. Most of it is plain bare metal. Would it make sense to put some standard pipe insulation on this rather than expose it to the hot temps inside the engine compartment?

 

<div class='quotetop'>QUOTE(jeromep @ Jul 27 2006, 01:14 PM) [snapback]293305[/snapback]</div>

regarding the variable speed A/C compressor, does this apply to the classic prius also?

 

The system is pretty good, heas up fast and cools down fast. Could use a little more air volume when cooling due to a large amount of solar radiant heating. Kinda like Global Prius Warming! ;-)

Toyota should really have called it "Climate Control" and not "A/C" there would be less confusion. Plus then it could have three settings; Heat, Cool, GW Reducing!

 

<div class='quotetop'>QUOTE(nitewolfgtr @ May 4 2007, 10:47 AM) [snapback]435528[/snapback]</div>

Classic Prius has belt driven A/C, which by its nature is variable speed, but variable based upon engine RPM. The Classic Prius still has auto climate, but that auto climate system engages the ICE for the purpose of running the A/C compressor. Not nearly as efficient a design as using an electric compressor.

<div class='quotetop'>QUOTE(Devil's Advocate @ May 4 2007, 11:26 AM) [snapback]435571[/snapback]</div>

That is kind of funny, actually.


Anyway, I decided to find my window sticker and see what Toyota calls the auto climate system. Toyota called it, at least in MY 2005, "Auto climate control w/air filtration. So, they do call it auto climate control, just as the rest of the domestic manufacturers call it, but that light on the dash confuses all of us.

 

yea the 01-03 prius's had a conventional a/c compressor, actually its the same compressor used on the MR2

 

<div class='quotetop'>QUOTE(jeromep @ Jul 27 2006, 08:14 PM) [snapback]293305[/snapback]</div>

Good explanation of how the climate control (that's the word we use here, although it does not really control global warming) works. I.m.o., there is one good reason apart from mpg to use the 'defeat' switch though: to dry the condenser, so it does not get smelly. That's why I try to avoid using the compressor when it's very humid: the part that cools the air also gets very wet. Just like a cold glass of lemonade on a warm and humid day. If you leave it like that when you turn off the car, it becomes a nice place for all kinds of fungi to grow.

It's easy to see when the system is humid. If you turn off the compressor on a cool, not very humid day and your windows fog up, that's a sure sign of water in there. Keep in turned off on on a cool and dry day, and turn up the fan until your windows stay clear. Keep the compressor off for a while, but remember to run it every month or more often.

 

Hello, I'm a new member and I have a questions about A/C.

I have a 2006 which I bought a few weeks ago.

When the A/C comes on, it just cools for a few minutes. Then heat starts coming out of the vents.

Do I need a recharge and do I need to take it to a dealer for this?
Is there something else I should check first?

Aside from that, I am happy with getting 51 mpg.

Any advice would be much appreciated, Thanks.

 

<div class='quotetop'>QUOTE(flashingsteve @ May 16 2007, 01:42 PM) [snapback]443544[/snapback]</div>

Does this happen independent of the temperature in the car? I mean, is the A/C always on for the same amount of time no matter how hot it is in the car? If not, it may be that it's cooling until it reaches the set temperature and then stopping its cooling. What temperature do you have the climate control set to?

I'm not sure what mileage you have, but it's hard to imagine that the A/C system on an '06 should need a recharge this early. . .

 

<div class='quotetop'>QUOTE(Betelgeuse @ May 16 2007, 01:49 PM) [snapback]443548[/snapback]</div>

Thanks very much for taking the time to help me with this.

This happens when it is set to "coldest possible" I think is the term used.
This happens even if it is just set to any temperature lower than the stated outside temperature.

The hot air that eventually comes out seems to be much warmer than the outside air.

And it does not shut off - it just keeps pumping out hot air till I shut it off manually.

 

Head to the dealer!

 

<div class='quotetop'>QUOTE(craigcush @ May 16 2007, 03:00 PM) [snapback]443620[/snapback]</div>

Ok - I have made an appointment.
Thanks for your replies and advice.