I’ve had the practice of setting my A/C on recirculation (or max) every time I get in the car and leaving it there, only turning the fan down as the car gets cooler, but never opening the vent. I went to do some research on the new Toyota Prius, however, and for maximum fuel efficiency, they recommend you use the A/C Max function as little as possible. To me, it seems like the air conditioner would have to do less and less work as the interior of the car cooled down, but does the power needed for the extra fan outweigh that benefit?
I believe this is how it works (sadly):
I don’t think the A/C has any variable power consumption at all. When you turn it on it functions at full power regardless of the other settings. The other settings will effect the temperature, but there is no way to get better fuel efficiency except by turning off the A/C.
So. If you put it on recirculation it uses inside air instead of outside air. You should use inside air if it is cooler than the outside air (so this means when you first get into the car, if it has been sitting in the sun, you should open all the windows and put it on vent until the inside air is cooler than the outside; this happens very quickly).
If you turn down the fan I suspect this just makes the air in the car circulate less. That means that the coldest air will stay in the vicinity of the A/C cooling instead of in the cab. This is the most efficient way to raise the temperature in the cab without wasting the A/C. Later you can turn off the A/C and still enjoy reasonably cold air for a while.
If you turn the temperature dial (the one that varies from A/C to heater) this will mix in air heated by the engine. So this is not efficient. Except that using the A/C is the only way to dehumidify the air, so if you want the air heated and dehumidified you need to turn this dial.
I am not sure about this information. If anyone knows better please correct me.
I am not familiar with your model. On all the cars I have owned with AC, the recirculation/vent is separate.
Clearly recirculation is more efficient, especially in removing humidity (the reason it’s called “conditioning” and not “cooling”.) Vented is good though when you need fresh air for some reason.
IMHO you should only use the recirc when you first get in the car and until the car is comfy. If you use the vent instead as someone else posted, you are continuing to cool off the hot air from the outside. If you use the recirc, you are cooling off air that has already been cooled somewhat…and somewhat more…and somewhat more. This definitely cools off the car faster and takes less energy from the AC. Once you are comfy, turn on the fresh air so you are not driving in stale air throughout your drive.
Are we reading you OP right, SanibelMan? Your car has the vent/recirc slection tied into the same control as the power settings?
I’ve never seen that. My Mazda has a fan with several speed settings, a button to switch between vent/recirc, an AC on/off button, and a temperature dial.
I agree with others, recirculating is more efficient than venting.
First, I can NEVER understand people who put their air on recycle. You don’t like oxygen, or what? I KNOW one can sit in closed car/house/room for hours without feeling much difference, but the oxygen level drops a lot before you are forced to open a window. In the meantime, there’s more carbon dioxide, less oxygen, your thinking is increasingly sluggish. Oxygen is good. Depriving your system of the natural amount of oxygen in the air is bad.
The amount of effort your A/C uses is likely to be quite directly related to the amount of heat it has to remove. Once an A/C reaches a particularly temperature, it either shuts off, or just pushes fluid around. If the car’s air is recycled, then the air going into the A/C is almost the same temperature as the air coming out, so it’s easy to cool it. If you’re drawing air from 100 degree ambient temperature, and changing it to 60 degrees, that’s going to be enormously more effort for the A/C.
If you’re only shaving a couple degrees off the outside temperature, then the A/C won’t be working particularly hard.
Recirc blows harder and colder, so it cools quicker. If you have climate control then it will shut off quicker, saving energy, or you can just shut it off yourlself.
To clear up confusion: My climate controls have a recirc/vent button at top, buttons for each vent setting (panel, floor, bi-lev, defrost, panel/defrost), an A/C button, a fan power knob, and a temperature control knob.
Zwaldd, how does it save energy to shut off the recirc? If, say, the fan is on level four (highest speed) with vent open, isn’t that using more energy than fan on level two (medium speed) with recirc on?
On cars that allow you to choose between recirculated air and outside air, there is one situation that calls for recirc, and that is to get the coldest air conditioning. The system will blow colder air out the ducts when it’s taking in already cooled air than when it’s taking in hot outside air.
If the car has been sitting in the sun and is hot inside, do not use recirc (or max A/C) until it starts getting some cooling inside. Taking in 95 degree outside is better than taking in 120 degree inside air. When it’s cooled down a bit, switch to recirc or max A/C.
If you would rather have outside air coming in, and if it gets cold enough to suit you, select the outside air position. If you would rather avoid outside air (e.g. driving through a dead skunk zone), select recirc. And of course if you want colder air than you get with outside air, select recirc.
Do not use recirc for heat, defrost, or vent functions. For heat and defrost, a properly working heater will be more than hot enough. In recirc, it is much more likely to fog the windows. For vent, the whole point is to get outside air.
The recommendation to avoid recirc for better fuel mileage makes no sense to me. In recirc, the colder temperatures relate to lower pressures inside the A/C system, which means less work for the compressor. It should get better mileage.
On cars that have “A/C” and “Max A/C” positions instead of a “recirc” button, the max A/C includes the recirc function, and it is not possible to get recirc in any other mode. These systems typically turn the A/C compressor on when in the defrost mode to dehumidify the air coming in. On systems with an A/C on/off switch, it is wise to select A/C when using defrost to minimize fogging.
Recirc doesn’t necessarily mean the fan’s blowing harder, although it will usually sound different because you’re hearing the air influx. If there’s a noticeable difference in the air speed out of the ducts, it’s due to some quirk of the duct configuration.
I agree wholeheartedly with everything Gary T just said.
Air conditioning units can only lower the temperature of the air by so much at a time. I was at my mother’s house this past spring when she turned on her AC for the first time of the season. It was about 85 in the house and the air coming out of the registers felt very warm … warm enough that we got worried and called her boss (an HVAC engineer). He assured us that everything was probably alright and said we should give it an hour or so. Evidently, her energy-efficent AC unit is only rated at about 15 degrees of cooling, so 85 in meant about 70 out, which is pretty warm when you’re expecting it to feel like you’re standing in front of an open freezer. Sure enough, an hour or so later, it was about 75 in the house and the air coming out of the registers felt noticeably cooler.
I’m guessing it was about 60 degrees. 