Hi, Can anyone tell me whether using the air conditioning in your car increases fuel consumption, and if so, is it by an amount significant enough to make a difference to your petrol bill?

Regards:confused:

Originally posted by Necrokiller
Hi, Can anyone tell me whether using the air conditioning in your car increases fuel consumption, and if so, is it by an amount significant enough to make a difference to your petrol bill?

Regards:confused:

yep knocks about 8 - 10 miles pergallon off consumption.
i drive with mine on all year so i never notice, but when we run a 4x4 with it you can tell.
also reduces towing power as well.

Originally posted by Necrokiller
Hi, Can anyone tell me whether using the air conditioning in your car increases fuel consumption, and if so, is it by an amount significant enough to make a difference to your petrol bill?

Regards:confused: Depending on how often you use the aircon.....you will use around 5% more fuel than normal.

It also depends on the size of the engine in the vehicle.
I run a gas powered 4.0litre grand cherokee and its only around 2or3% but on smaller engines like 1.6 etc the power drain will be much more significant.

But the overall answer is YES it will use more fuel in ALL CASES.

Ive heard that if you have the windows open instead of the air con on, then the rag makes you use more petrol too???!!! So maybe just same ish.

Originally posted by pdrnsf
Ive heard that if you have the windows open instead of the air con on, then the rag makes you use more petrol too???!!! So maybe just same ish. Actually the reason why more fuel will be used when using an aircon system is that the energy required to turn the pump is taken from the engine thus in idle, when the aircon is switched on, there will be a drop in revolutions as the engine tries to supply the extra energy required for the pump to operate.

Average figures on Aircon-increased consumption are around 10%.
Window-open drag increases dramatically with speed and so it is interesting to hear one report that says Aircon becomes the more efficient method of cooling over 50 mph.

Cheers for the prompt replies guys

That has certainly cleared up the issue for me!

@pdrnsf I can see what you're saying about the window thing, I reckon the drag caused by having your windows open makes your car less efficient than having the air con on and the windows closed does!

The window thing is fast becoming an old wives tale. Perhaps with the Grand Cherokee described above it could make more difference at legal speeds.

Turn your aircon on on the mway and monitor the extra air intake required to maintain speed with a vacuum gauge. Monitor it with a window down = aircon makes more difference for me.

Originally posted by Trickle
The window thing is fast becoming an old wives tale. Perhaps with the Grand Cherokee described above it could make more difference at legal speeds.

Turn your aircon on on the mway and monitor the extra air intake required to maintain speed with a vacuum gauge. Monitor it with a window down = aircon makes more difference for me.

air intake?

If you measure how much air is going into the engine, then you know how much petrol is being used :) [roughly]

If I have my aircon on, I can tell simply by the fact that acceleration is blunted. My Ecu is supposed to cut the aircon under acceleration, but only seems to when flooring it.

I've got a bora turbo diesel. with the AC on it's difficult to detect any loss of power, I guess because diesels have more torque.

very little loss of MPG, maybe 2-4mpg at most.

much more noticable is loss of MPG when carrying stuff on the roof.

Motorway MPG = 60 unladen. Low 40's with bikes and roofbox on.

my old mondeo 2 litre petrol had noticeable loss of power with AC on.

John

They tested this on mythbusters (Discovery) by driving around a track with aircon on, and then with windows open.

Only problem is I cant remember what the result was - I remember it being unexpected though!:rolleyes:

It's clear that airconditioning requires power, it has to be plugged into the electrics if it's not in a car, and it's basically a refrigerator in reverse, so it's not going to work without power.

Since the only source of power in a car is the engine, that has to be where the power comes from for the a/c.
I've been asked before why it doesn't run off the battery, the battery in a car only provides electrics when the engine is off, when the engine is running electrical power comes from the engine via the alternator/distributor. The battery otherwise would clearly not last the length of an average journey with the a/c on.

The amount of energy wasted through friction is dependant in part on the cars drag co-efficient. Ie the more the car is aerodynamic, the less the drag and the less power required to maintain a constant speed.
Opening the windows causes turbulence and thus increases the drag coefficient.

As to which is better, windows down or a/c on, who cares. A/c on is far more effective than windows down on a hot day, so close your window and put on the a/c

Personally I loose about 2 - 3 mpg with it on, but I loose more than that if I use a heavy right foot, so it's not significant.

Originally posted by floyd77

Only problem is I cant remember what the result was - I remember it being unexpected though!:rolleyes: Thanks Floyd, I knew I read that from a recent test too :) A quick google search reveals:

Well, Mythbusters on The Discovery Channel proved at different speeds that air con uses far more fuel, having the windows down is far more economical.

I`ve got a 1.2 fiesta and with the air con on it runs b***dy awful. I tend not to bother with it just put it on for a few minutes a month to keep it working.

The air con on my Honda Fireblade is proper rubbish.

The air con on my Honda Fireblade is proper rubbish.
Ride with your visor up or get an open face helmet. It`ll work a lot better then. I find it works better when i try this on my Yam

Ride with your visor up or get an open face helmet. It`ll work a lot better then. I find it works better when i try this on my Yam

Two things:-

1. I don't own a motor bike.
2. I was joking.

Thanks for the advive anyway.

I've got a bora turbo diesel. with the AC on it's difficult to detect any loss of power, I guess because diesels have more torque.

very little loss of MPG, maybe 2-4mpg at most.

much more noticable is loss of MPG when carrying stuff on the roof.

Motorway MPG = 60 unladen. Low 40's with bikes and roofbox on.

my old mondeo 2 litre petrol had noticeable loss of power with AC on.

John

Interesting that. I've got a Bora 2.0 petrol and the difference in fuel consumption with the A/C on is about 2-3 mpg.

Interesting that. I've got a Bora 2.0 petrol and the difference in fuel consumption with the A/C on is about 2-3 mpg.

Yes, fascinating.

yep knocks about 8 - 10 miles pergallon off consumption.
i drive with mine on all year so i never notice, but when we run a 4x4 with it you can tell.
also reduces towing power as well.

why would you keep your A/C on in winter? I don't understand.

Ive heard that if you have the windows open instead of the air con on, then the rag makes you use more petrol too???!!! So maybe just same ish.


I was told this too, windows and sunroofs create drag using more fuel equivalent to the extra used to run a air-con unit, Swings and round abouts really.

why would you keep your A/C on in winter? I don't understand.

Air-con clears mist off windows on a winters morning , also needs using regularly to maintain performance.

Ive heard that if you have the windows open instead of the air con on, then the rag makes you use more petrol too???!!! So maybe just same ish.

Yep, by having the windows open you introduce more drag so the car has to work harder to make you go at the same speed. It's all aerodynamics, drag co-efficients and what not :) http://en.wikipedia.org/wiki/Drag_coefficient