I've got conflicting takes on this. I've always thought it burns more gas. But I'm not sure about overworking the engine.

u could drive with ac any where u wish, but its true that it puts more load on the engine. infact its the extra load on the engine that is actually bringin about the consumption of more gas. hope this post would be useful but i'll still try to carry out further research & get back 2 u. cheers

it's summer, what do you think? Put the damn ac on.

If its fuel consumption you are concerned about, driving the the AC at speeds above 55mph(88km/h) is more efficient than leaving the windows down at such speeds. The reduced aerodynamic drag compensates the increased stress on the engine. Its when AC is used in stop and go traffic that the consumption increases dramatically.

A good tactic would be to turn on your AC once you get on the highway and turn it off once you get off. The irony is that its in those stop and go traffic that you REALLY need the AC, so only do this if you don't mind the heat.

Straying from the topic a bit, I've always wondered why there is no wet suit for terrestrial purposes. It would reduce the need for AC significantly because water is a very good insulator from heat or cold. thats how come scuba divers don't go into hypothermia (low body temp.) without wearing huge coats. The thin layer of water trapped in between the wet suit insulates them from the surrounding cold water.

Yeah, it burns fuel, from what I heard, but its purpose is to refresh you, during the stifling heat. Dont you want to drive in comfort during heat, knowing fully well that your gas would eventually run out, AC or no AC?

You better put your ac on before you are robbed in traffic (only applicable to lagos inhabitants)

@uchetobi

WORD !!!

Yes o I agree on that but even PH residents should be cautious too.
I was waiting for traffic at Garrison in PH and a guy nearly robbed me. He attempted to open my doors but because I ALWAYS drive with my doors locked he could not gain entrance into my car, then he pretended like a Berger and motioned me to wind down which of course I refused and at that point he started yelling at me. 'I dey beg u now and u no go use ur church mind find me something now' next thing he did, was bend down and tried to deflect my tyre hopping that I might wind down or come out of the car. I was so grateful that the traffic wadden passed my line and you can imagine the roar of my engine, I could have crushed anybody on my way at that point.
Bottom line: The stop and go traffic is the best time to use the AC since I could wind down my windows when on high way but all these is still assuming you are living in Naija.

naijadey:

If its fuel consumption you are concerned about, driving the the AC at speeds above 55mph(88km/h) is more efficient than leaving the windows down at such speeds. The reduced aerodynamic drag compensates the increased stress on the engine. Its when AC is used in stop and go traffic that the consumption increases dramatically.

A good tactic would be to turn on your AC once you get on the highway and turn it off once you get off. The irony is that its in those stop and go traffic that you REALLY need the AC, so only do this if you don't mind the heat.

Straying from the topic a bit, I've always wondered why there is no wet suit for terrestrial purposes. It would reduce the need for AC significantly because water is a very good insulator from heat or cold. thats how come scuba divers don't go into hypothermia (low body temp.) without wearing huge coats. The thin layer of water trapped in between the wet suit insulates them from the surrounding cold water.

SUMS IT ALL UP. It is a balance between the aerodynaic drag created by the open windows, and the extra load on the engine by the AC which reduces the mileage per gallon (or litre, whichever measurement you take).

But in Port Harcourt with all the touts around, driving with your AC may be the best option to prevent being robbed or attacked by these hoodlums.

NB: Even if you have no A/C, this option will help you o!. I was once attacked in similar circumstances. Luckily, the guy I was driving with was a Deputy Superintendent of Police who did not hesitate to put his service pistol to good use, saving us some embarrassment.

It's good 2 drive with AC on the highway b/cos if you are driving above 140ph i think u gotta put it on.point of correction factory fit AC does not consume fuel. so get chilled in your car and stop looking around to buy satchet water think about it.

4 christs sakes! would u rather roast in the heat?

Whoever said "Turn your AC on on the highway and off on the streets makes MAXIMUM and PRACTICAL sense"

Why you should leave ur windows down on the street or in a traffic jam:

1. Apongbon boys killed a lady last year while trying to smash her windows in a bid to snatch her phone from her. The rod mistakenly went into her left side (and hit the heart) she died 2 hours after.

2. Apongbon, Osbourne Road, Ijora, Cement and a host of lagos traffic spots have witnessed massive daylight robbery and woe betide u if ur A/C's on at that time. You won't only lose your windows, you'll lose your phones and maybe, your life or pay some medical bills.

Una don hear me so? On the streets of lag, errbody gotta play STREETZ. Leave ur windows down and switch ur a/c on if you wish.

Haba why doing ijebu while u know that u are able, A/C in the car makes u to fell cool and fresh, infact ur mined will be focus, the issue of noise distraction we be out, very good and ideal if u do not want to economize ur fuel.

shuo, if u no go use ur AC y did u install it?
As far as I know, ma uncle's car burns more fuel wen on AC
but d fact is that, its really ok driving on AC just that u will need some extra fuel
though not much as in u begin to think of doubling the ur purchase

Exactly! If AC was not meant to be used, why was it put in the car in the first place? Of course it will definitely stress the engine, but don't you think that was put into consideration before the car was manufactured? Do you know the amount of other things that stress the engine in your car? I think it's up to you to decide if you want AC or not.

Hi,
Some one said: "point of correction factory fit AC does not consume fuel."
No, A/C does not use fuel, but when it is turned on, it puts a load on the engine, and therefor causes the engine to use more fuel.
You can test this when the engine is at idle, just turn on the A/C and listen to the change in the engine note. On some newer cars, the engine will even speed up slightly, this is programed in to compensate for the A/C.
You can also apply the same test to the electrical system, by turning on heavy electrical load (such as a rear window heater) and you will hear the engine change note also.
Regards.

The A/C of my car does not bring about increase in fuel consumption.

Yes, the sound of the engine changes when you put on your AC. That does not affect at all the rpm of your engine (unless it is not factory-fitted).

The fuel consumption of your car is a function of how many rotation per minute (rpm) your engine crankshaft does. The rpm of my car remains the same (900) when the engine is idling whether the AC is on or off.

If you mismatch a powerful compressor probably from a 2.0l engine to a 1.8l engine, ofcourse it will draw the engine down and burn more fuel.

If its fuel consumption you are concerned about, driving the the AC at speeds above 55mph(88km/h) is more efficient than leaving the windows down at such speeds. The reduced aerodynamic drag compensates the increased stress on the engine. Its when AC is used in stop and go traffic that the consumption increases dramatically.

I do agree with your points, but fuel consumption increases in stop and go traffic regardless of whether the a/c is on or not. The greatest consumption time is at take off, as you can see the consumption increase according to your take off speed.

When I turn my car a/c on at stand still, although I do notice a slight change in the car, if the fuel consumption has peaked at traffic conditions , the on board computer still shows the same fuel consumption. If the car is in motion, no change is noticed and if the fuel consumption is on the decline before turning on the a/c it continues to fall until it gets to the optimum level. That is contrary to my expectations, but may be it is because I only turn the a/c on slightly if it is not on auto climate control.

When I switch off the a/c on the motor way, the fuel consumption does not improve. According to the on board computer in the car, a/c does not affect fuel consumption, at least not at low level a/c as I am used to.

Fuel consumption also depends on how warm your engine is. It improves from cold start and peaks after a while.

To achieve the best fuel economy, do not speed excessively. I have noticed that my most economic driving condition is achieved at low speed and high gears. Cruising at between 50 & 60 MPH, I have achieved 43MPG on the 6th gear with a/c on, but have only managed 39MPG between 70 & 110MPH.

suffering can be bliss for some people!

driving with the AC on on the highway takes less gas than using the AC while on the city streets, so i would advice u to turn it on once u get on the highway. i personally believe its a luxury one can afford to have

Thanks to all those that really understood the question posed. It's not about the cost of using A/C but rather to dispel some widely held misconceptions. Many folks are prone to turn off A/C on the highway for variety of reasons, even when it's more convenient to travel long distance with it. And if the reason is gas conservation, it's good to know that the drag caused by open windows actually burns more gas than using A/C.

Wow this is really cool. I like hearing the smart and intellectual arguments in the house. Keep it up my engineers. Its topics and posts like these that make nairaland worth visiting once a while.
But I have a question; do these replies apply to my ferrari, since it already has a sweet streamlined shape, i wld think that air resistance due to drag would be less on it. What do u guys think?

Guys I hear You, but did any body consider the size of engine on the effect of gas consumption? If you think about that, effect of AC on Gas is Yam (Nothing).
I have friends driving Big cars and trucks and their engine ranges from V6 to V10 and I am talking about 4.6L engines to 6.0L
If they can drive that, the last thing to bother about is Effects of AC on Gas consumption.
So Guys enjoy that Harmattan wey dey inside your car.

I hail Una.

Guys I hear You, but did any body consider the size of engine on the effect of gas consumption? If you think about that, effect of AC on Gas is Yam (Nothing).
I have friends driving Big cars and trucks and their engine ranges from V6 to V10 and I am talking about 4.6L engines to 6.0L
If they can drive that, the last thing to bother about is Effects of AC on Gas consumption.
So Guys enjoy that Harmattan wey dey inside your car.

I hail Una.

naijadey:


. . . Straying from the topic a bit, I've always wondered why there is no wet suit for terrestrial purposes. It would reduce the need for AC significantly because water is a very good insulator from heat or cold. thats how come scuba divers don't  go into hypothermia (low body temp.) without wearing huge coats. The thin layer of water trapped in between the wet suit insulates them from the surrounding cold  water.

I don't think it would be a good idea.

check the data below
Thermal Conductivity - k - (W/m K)

Air , 0.025
Alcohol or oil , 0.15
Aluminium , 220
Cork , 0.05
Glass , 1.1
Rubber , 0.16
Sandstone , 2.4
Soil , 0.15
Stainless steel , 15
Water , 0.58
Wood , 0.04 – 0.4

Rhea:

The A/C of my car does not bring about increase in fuel consumption.

Yes, the sound of the engine changes when you put on your AC. That does not affect at all the rpm of your engine (unless it is not factory-fitted).

The fuel consumption of your car is a function of how many rotation per minute (rpm) your engine crankshaft does. The rpm of my car remains the same (900) when the engine is idling whether the AC is on or off.
If you mismatch a powerful compressor probably from a 2.0l engine to a 1.8l engine, ofcourse it will draw the engine down and burn more fuel.

rpm of a car is analogous to stm (step per minute) of human.
this is obviously not an absolute indication of the quantity of *eba to be consumed after performing a feat of 100meters dash in 9.09 secs.

the engine rotation per minute may remain the same but it depends on how the car was programmed

For instance, you can carry a bucket of water and run 100 meters in 15 secs.
and you can run at the same speed without carrying the bucket of water.
but we all know which is more difficult.

bottom line, your engine will use up more petrol to do any additional power generated by your car either in closing the window or running the AC.

In physics, power  =work / time
the more the power required, the more the fuel required to do the work.
the two functions are proportional.


* eba - a nigerian staple food (98% carbohydrate, 2% fiber and silica/stones)

Hi,
Stranger12 is right on with what he says about the load and fuel usage. It is the same thing that I tried to get across in my other message.
Regards.

yeah! With the A/C on and windows up, you've got a lesser drag than when windows are down. Adams and Jamie of mythbusters did a great work on that.

You save gas and have minimal drag.  Today's cars are built  aerodynamically with all windows up.  Anything higher than 30 miles per hour is not a bargain with your windows down. 

Using your A/C rubs you of torque (but minimal). You'll burn gas with/without if you go floor from 65 - 80 because your engine has to do a leap at this point. You also burn higher when you exceed 60MPH. With all my studys, I have come to the conclusion that no car saves gasoline. They all burn the same way with weight and breathe pattern factored in. cd's play a little role in this too. American cars are just an exception (gas wells). Some people believe a 4 cylinder will on gas. Well, true if all you are doing is stop-and-go. It would cost you a lot more fuel to get your pistons to rev at 4500RPM and having your transmission rotarize it in a 4 cylinder than a 6 cylinder. This is due to the fact that a cycle in a 6 cylinder is completed every 60 degrees as oppose to the 90 degrees done on a 4 cylinder. In a 4 cylinder, your engine just revs, makes noise and takes forever to pick that speed up.

Mercedes' with E's on them have a different way of fuel management. The injection on the '63 280SEL is what many cars started to mimic in the late 90's. They were the first and still leaders in injection engines.

@stranger12,

WORD.

Allwell:

yeah! With the A/C on and windows up, you've got a lesser drag than when windows are down. Adams and Jamie of mythbusters did a great work on that.

Again, it depends.


A = drag on motorway (@100km/hr)

B =  force required to keep the A/C on.

use your A/C if B < A  . . . . its economical

use your A/C if B > A . . . . its cools the mind


Don't be kobo wise and naira foolish.

As long as Nigeria is concerned (Lagos in particular) always drive with your AC on. It protects you from a lot of things - noise, dirt, awful smells, touts and it keeps you refreshed. As long as your car is still in good shape, preferrably almost new, you dont need to worry about fuel consumption.

stranger12:

Again, it depends.


A = drag on motorway (@100km/hr)

B =  force required to keep the A/C on.

use your A/C if B < A  . . . . its economical

use your A/C if B > A . . . . its cools the mind


Don't be kobo wise and naira foolish.

Vehicle Dynamics and Stability Control works by principle.  There is drag as low as 35MPH (and for some cars, worse).   Your theory does not get along.  It's way off and cannot be proven kinematically.  The air conditioner robs your vehicle of torque because it requires some horsepower to set it in motion.  A compressor-like motor is what saps power.  The only way to by-pass this rule is to get an electric compressor (as race-tuned vehicle are fitted) but you'll need bigger a bigger battery and a bigger alternator and some other modifications that will eventually lead to electrical problems.  Cars today are built aerodynamically with all the windows up.  The only exception to this rule (and not limited to) is a convertible.  The engineering to this requires a lot more research and developments that's why it costs more than the normal car with more materials and weight.

100KPH should approx. 70MPH.  Fuel consumption in a car burns dynamically.  In other words, it doesn't burn linearly but dynamically.  You get the best mileage at 55MPH (applies to all cylinders) and the worst as your car moves from 80 - 110 MPH.  After 110, it doesn't take much for your engine to propel your vehicle.  Your car better be properly maintained to this.   You better not be driving a Honda for this; the laws of physics will not change.  The faster an object goes, the lighter it becomes, thus becoming lighter than the air surrounding it.  I am not saying it will airbourne but a great deal of stability would have been compromised.  Most cars, expecially the 4 cylinders don't reach it's stated maximum speed dispayed on the speedometer.

sojioguns:

As long as Nigeria is concerned (Lagos in particular) always drive with your AC on. It protects you from a lot of things - noise, dirt, awful smells, touts and it keeps you refreshed. As long as your car is still in good shape, preferrably almost new, you don't need to worry about fuel consumption.

It doesn't matter if your car is old or new.  A/C robs you of throttle response and also diminishes your gas mileage.  Also, your alternator would be running twice as much and that also requires fuel to power and do its conversion.  There will be a pitiful experience if your engine isn't healthy enough.  As we all know, many factors are responsible for that.  It's also interesting to note how your A/C keeps you from smell, noise and sound.   In the United States, it is illegal to alter your car to the state of which where external sounds are almost inaudible or virtually eliminated.  Library-Quiet requires firewalls, dampers as well as deadeners to keep engine and road noise from the inner cabin but allows what sounds (of which is permitted by law) to wave through.  There is no restriction to what happens within the cabin.