Protan988

Hey guys I just have a quick question hopefully you guys can answer.

When you have a/c on will it cause you to go through more gas if you set the fan on full blast vs just on medium or low? In my mind I think the compressor has a clutch and as soon as you turn on the a/c the clutch kicks in so that no matter what fan speed the a/c would be the same for gas mileage?

Correct me if im wrong. Thanks.

unTuned

yea ive always wondered this too and i thought the exact same thing. thats why when i have ac on, its either full blast, or its completely off.

anyone know for sure?

Ckutch02EX

I can't say for sure but it would make sense that the higher the setting the more gas you would use because the compressor is working harder. Think of it like a home ac. You use more electricity if you have it turned to a higher setting. Makes sense to me. Could be wrong.

rednwhite04

iTrader: (3)

the a/c on 7th gens and most new cars runs on a magnetic clutch, which causes no resistance= no change in MPG. This was also covered on Mythbusters "windows down or a/c on"

Ckutch02EX

It all has to do with speed. Your mileage will go down if you use air conditioning below 30mph as apposed to windows down. If your over 30 it's better to use air conditioning however it would make sense that the higher you have it cranked the more gas is used. Thats why you feel a loss power.

batman900

iTrader: (1)

I also wonder this. However I dont think it matters about the speed, if its on then it is using power to cool and "does" effect gas mpg, but the only dif between how hard its blowing is your fan speed, it doesnt have to work harder to cool the air just because the air is being blown at you faster. I also saw the mythbuster episode, they confirmed you lose mpg with it on but that its better to have it on at speeds over 40mph rather than have your windows down, because the wind resistance hurt mpg more than the AC did at that speed and onwards.

Ckutch02EX

^^^30 40mph. same point. Thanks for the backup

gearbox

iTrader: (95)

your fan uses more electricity at full power.

lowlife9

good to know. did you see the one were they filterd fryer oil threw a coffee filter and ran it perfectly in a mercedes diesel with no problems.

Awjvail

So it's more fuel efficient to leave my windows down while traveling under 40mph, and above it is better to have the AC on? Let me get that straight.

Just a question - a lot of the time when I'm traveling on the highway, I like to just have the windows up and have the fan blowing with the AC off - just to circulate some air. Does this affect gas mileage at all?

gearbox

iTrader: (95)

well yeah it will use power, but prolly not that much. with the fan off and going fast, air still comes thru the vents if you have it switched to fresh air mode. so you may not even need to turn the fan on to get fresh air blowing inside.

Protan988

Lol so nobody has an answer? I know its more fuel efficent to use a/c on the highway buy my question was never answered. Im assuming that it doesnt matter how much the fan is on. It will just use a bit more electricity. I dont even know if that would effect your mpg that much. Anyways can we agree that it wont affect your mpg then if your fan setting is low or high?

wallydude03

Once your ac is on, it is on. It doesnt matter how hard the fan is blowing.

CraigW

iTrader: (1)

Yes, The fan speed has no bearing on how long the A/C clutch stays engaged. The decrease in gas mileage due to the increased current required for the faster fan would be minimal.

lowlife9

what if your windows are down but you have wind deflectors then there would be little to no drag ??? did the mythbusters test that.

unTuned

haha this is getting out of hand!

Atromos

Even though the clutch is magnetic, it still steals engine power. Just because it isn't touching doesn't mean there is no force on it (how do you think electric motors work?... magnets).

To answer your question, your A/C may or may not have a thermometer on it telling it when it is at maximum cold and will shut the compressor off until it warms up.... or maybe it keeps running all the time. I know that if I turn on the A/C in my civic to 100%, it's not as cold as 80% so I don't think the compressor has an on/off switch... it's obviously incredibly weak and doesn't cool the car as quickly as a luxury car does. Just put on your A/C and drive 40+, you're worth it ;D.

Protan988

I try to avoid a/c as much as possible I usually get 600-630kms per tank. My fiances mother is down right now and she likes a/c and it has been on almost all the time and i was only getting 500km per tank. Thats a huge difference and that was a fair amount of highway driving too.

cloud2987

In my class in automotive service my instructor (ASE Master Technician) told us that on most cars if you go over 45mph the fans wont use electricity since the fans will be spinning anyways. So your engine wouldn't have that extra load so your MPG would be more efficient. I don't know for sure if that goes for Civics as well, but it makes sense to me.