Understanding the A/C Buttons

1) More efficient, perhaps, depending on the temperature difference, but some people like fresh air. In my Gen II on a long trip, I notice the difference in my level of alertness within minutes - my preferred setting is always to bring in outside air.

2) A common misconception. 'Conditioning' does not necessarily mean 'cooling'. It also means warming and drying - outside air is being conditioned to the set preferences. Just because the ac icon is lit, that doesn't mean the air is being cooled.

 

Recirculated -- is just that --- the air being heated or cooled is coming from inside the car - normally the ACC (automatic climate control) still brings in some outside air .. but some don't ....... the outside air flap completely closes ... I'm not sure how the Toyota system flaps are set up. You should only use this when you get behind a truck that has a strong exhaust or you see a dust cloud coming. Some ACC systems will actually turn the "recirculation" off after a predetermined amount of time -- say 10 min. You will also see that the ACC will switch to "recirculate" when you first start up to quickly cool the car. Some cars are so tight that you will reduce the amount of O2 in the air.

As to the AC switch: Every manufacturer does this a bit different but they all work about the same way. If the AC button is not lit then the AAC will not turn on the compressor. Some call this "econ" other systems will turn off the "auto" light when the AC button is not lit - since you are technically no longer in "auto". The toyota jsut has the AC button lit or off.

I always leave mine "on" -- so the system can dehumidify the air and keep the windows clear -- you will also find that the air in the car will be much fresher. When it is very cold out the system inhibits the compressor from going on. Outside air enters the cabin and crosses the air filter -- then through the AC condenser to remove moisture and then over the heater core if heat is required.

 

The Prius brings in small amount of outside air even when in recirc. One reason for doing this is for positive pressure to keep air flow through the cabin and out through the rear vent to the HV battery for cooling and another is as you state to keep fresh O2 in the cabin. The only time that it closes the fresh air vent door completely is when you press the Dust-Pollen button and then only for a three minute duration. During this time a flap will open and pull air from under the passenger floor area for recirc.

If you leave the system in Auto it will do a good job of using recirc to quickly cool the car and then to fresh air once the cabin cools down.

 

I usually leave mine on Fresh, not sure if I have a good reason for doing so, though outdoor air is typically less polluted than indoor air. There are some times where Fresh is more economical than Recirc, though; for example, cooling your car after it has been parked in the sun (so the air inside the car will be significantly hotter than the outside air.

Fresh air can also help in some conditions where the windshield is fogging; the air in the car is at, say 70°F and 100% relative humidity. The air outside the car might be at 50°F and 100% RH, but heating that air to 70° will drop the relative humidity to just 50%, allowing you to clear the windshield with just heat. Using recirculated air, the car would have to use air conditioning to drop the temperature and dry the air, then heat to bring it back up to the desired temperature.

Also, in general, just like the Recirculated setting on most cars still brings in 20-30% fresh air, the Fresh mode typically brings in 10-20% recirculated air to help efficiency a bit.

 

That's good to know about the AC being on. When I first learned to drive, I think my dad told me that I would fry the compressor if I had the AC on, but selected a temperature that was warmer than the outside or cabin air temperature. I have been afraid of that ever since.

Is this true of all cars or just the Prius?

 

On virtually all modern cars, if you set the temperature to warm with AC selected will first cool (and dehumidify) the air then rewarm it with the heater core. Very helpful on cold, rainy days.

- Chris

 

Years ago it was common for people to turn off the AC prior to shutting off the car -- this was so that on startup the starter motor did not have to turn both the engine and the AC compressor. Same goes for accessories with battery capacity and alternator drain.

Non of this applies today and has not for years as conventional cars keep all of these off until the car starts -- plus batteries have greater capacity and starter motors are stronger.

Also -- AC systems are protected and controlled by many sensors that manage and protect the system. Years ago it was compressor "on" or "off".

 

If your on the highway and it's cool outside and warm inside, like on a cool sunny day, you can leave the system off and get cool outside air through the vents. Of course you need to have outside air selected and the temperature needs to be set lower than the inside temperature of the car.

Even with the heating AC system off the temperature setting and recirculate on/off are still effective and it will switch from floor to dash vents when the interior comes up to the temperature you set when the system was on.

 

This is still a good idea, though perhaps for different reasons. Circulating warm air through the system helps to remove moisture from the coil and ducts, which otherwise tend to go mouldy and cause a stink.

 

Many reasons, pick any that may apply to your situation:

* Energy efficiency -- in my climate, fresh air is usually sufficiently cool to avoid the need for AC cooling;

* Odor control -- if any passenger is having a gassy day, fresh air reduces the gagging factor;

* Moisture control -- human respiration always puts moisture into the air, and some weather conditions bring in much more moisture on their clothing and footware. Unless fresh outside air is flushing this humidity to the outside, or the AC is actively drying the interior, the window surfaces will often fall below the dew point in my climate, causing vision-hampering window condensation;

* Toxic fume control -- in the old days, vehicles were not well sealed, and became leakier with age. The slipstream around some gaps or failed seals or corrosion perforations would suck air out of the vehicle, causing makeup air to enter at other openings. Some of these openings would draw in exhaust fumes from under or behind the vehicle. Even in the 1980s I was seeing newspaper reports, typically once per year, of kid(s) 'sleeping' in the back seat being found dead of carbon monoxide poisoning. I now believe this CO intake was the cause of some of my own frequent childhood car sickness.

Forced fresh air intake, sourced ahead of the engine, pressurizes the cabin to abolish the vacuum that can suck in fumes through gaps. If this is insufficient, the frequent air changes limit the CO buildup;

* Dust control -- same intake mechanism as above. As a kid living at the end of a dusty gravel road, I often watched thick dust streams pour in through door seal gaps. Pressurizing the cabin with clean air sourced ahead of the dust-raising wheels greatly reduces this mess.

 

I was always told that re-circulation is much more efficient when running the AC - as said earlier it has more to do with dehumidifying the air than cooling - using the recirculation there is less moisture in the air.

Just the opposite with the heat. I always thought that by bringing in outside air it actually helps the engine run a little cooler by brining cooler air in and dispersing the engine heat(that is why it helps to turn the heater on if your car is overheating). But it also helps keep the window fog down on really cold days.

 

I choose outside air whenever I fart in the car.

 

Use Fresh setting if your passenger or your self had a huge serving of beans.

 

My nine-year-old and some hard boiled eggs can make me keep it on fresh air...

 

Reminds me of my days frequenting the local White Castle.