AC MYTHS
 

I really hate it when I'm sitting in my friends car on a hot day, and he/she turns on the ac but keeps the fan on 1 or 2. They think they are using up less "AC" by keeping the fan setting on low. My understanding it that once the AC is on, it doesn't matter what setting the fan is on. It doesn't cost any more to run the ac with the fans on full, then it doesn at 1. I'll list some of the myths or questions I have about AC and hopefully the wiser will share some insight.

1. Does the fan speed make a difference on the load your car gets from the AC?

2. Which is more efficient "fresh" or "recyle" setting for air circulation? - does it matter whether the car is warmed up or not?

3. A honda mechanic once told us that it cost less to run the ac on full blast, then to drive on the freeway with your windows open. -is it true?, for the S2000 anaways.

4. What really are the costs of running the "AC" on the S2000, if there's any way to calculate it?

that's all I can think of right now, but I'm sure someone else will cover what I missed.

1. It sure does in my beater :LOL: (96' toyota tercel).

2. Does what matter if its warmed up?

3. I would say its pretty darn close. Windows down has a drag effect on the vehicle and the AC on has a drag effect on a belt connected to your crank.

4. Gas mileage? differences between AC on and no AC.

:hello:

2. Does what matter if its warmed up?

-using "fresh" or "recycle" settings. I've heard something like start out with recycle, then change to fresh or something.

4. Gas mileage? differences between AC on and no AC.

-well yeah, but I'm sure someone here has calculated the actual difference in gas mileage.


Oh, and who is that on your sig. she looks tasty.

Sounds like typical desi/waniya behavior. Are you referring to 'cost' in terms of fuel or power?

Do a simple test. Travel a fixed distance on the same road under similar conditions (the farther the better). Monitor how much fuel you consume 1) with AC on full, 2) AC on low, 3) AC off.

Our AC's have a clutch mechanism so in the higher RPM, if I recall- something like over 7K rpm, the AC is turned off even if it is ON.

Sounds like typical desi/waniya behavior.

word, as long as you're reffering to the cars I'm sitting in and not me. cuz I don't hang out with either one's.

Are you referring to 'cost' in terms of fuel or power?

-both

Do a simple test. Travel a fixed distance on the same road under similar conditions (the farther the better). Monitor how much fuel you consume 1) with AC on full, 2) AC on low, 3) AC off.

-Damn, you're brilliant, why couldn't I have thgout of that. :banghead:
-this is an information sharing forum. If I wanted to go out and test everything myself, there won't be much of a need for the forum wold there? :confused:

Our AC's have a clutch mechanism so in the higher RPM, if I recall- something like over 7K rpm, the AC is turned off even if it is ON.

-good insight, I did not know that. I learn something new about this car all the times, and I've had it over 4 years now.

1. No. The A/C compressor pulley is "clutched" and will turn the compressor the same whether the fan is on the first setting or the highest setting. The only difference is the increased electrical draw of the fan turning at higher speeds.

2. Recycle simply pulls in cabin air, does the heat exchange and pushes it back out into the cabin. Initially after getting into a parked HOT car, recirc will cool the cabin down more quickly, but then you should switch to "fresh" or the air gets stale and you could promote mildew and bad smells forming in the A/C ductwork.

3. Don't know. The parasitic draw of the compressor and electrical draw of the fan (hence draw on the alternator) can be quite considerable. Is it better to turn it all off and have the windows open and accept the aerodynamic drag? Don't know. Don't care.

4. See point #3. Sure there is a way to calculate it. Go through a tank of gas with the A/C on all the time (and at least one fan speed). Never turn it off even if you turn off the car. Then go through a tank of gas with all of it turned off (no fan speed setting whatsoever or run fan but make sure A/C is OFF) if you can take the heat. Then compare fuel economy. I think you'll find that with A/C on, your fuel economy (given similar driving scenarios) will be in the sewer.

The AC unit is for passenger comfort.. I makes no difference what the efficiency is, any cost variance is so minor most of us will not worry about and use the unit to make the people in the car most comfortable.

the "under the hood" section of this forum is for technical data. If you don't like to get deep into things like this, you're probably not going to enjoy this. for the amont of money I spent partying on sat, I could probably run the AC for decades, so again this thread isn't about saving $. It's strictly informative. :) Thank You!

this would not really prove much, as there is far too many variables to eliminate in determining such a small change.

correct

also, by the way, mythbusters did this "test" and found that it was more efficient (at least for the vehicle they used) to use the AC on the freeway, then to leave the windows down.