Using air con will increase fuel consumption. Does anyone have any realistic/scientific idea about how much extra fuel air con uses?

Jimbo

It has a lot less effect on fuel consumption than it used to in the 80's. in those days in cruise control and engaging aircon the car would hesitate and you would hear the engine pick up as it regained the setting.
Common consent is it increases consumption 8 to 10% but uses less fuel than opening a window or windows, your option is either use it or cook  my PC is slightly to the right of Genghis
2012 HSE SD4 In Orkney Grey now gone, best car ever.

It seems to knock 2 or 3 mpg off my consumption when I use AirCon.

I just leave the Climate Control on AUTO all year round and never alter the temperature.

AirCon ON is selected for most of the summer (and for those damp cold days in the winter to stop the windows misting)

As said above the FL2 has bags of available power, and it is not like the 1980s when I used to only use the AirCon to help engine braking down long hills, as the power loss was very noticeable. FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 84k+ miles) (MY2015)
Metro in its 11th Year of (Extended) LR Warranty / Full LR Service History
(Expensive, but Trouble/Worry free - hopefully?)

Ive tried comparing with and without aircon,and cant see any difference in mpg,but my friends corsa with a small engine has a huge drop in mpg with aircon on.

On the FL2 the air on still works really well, never been touched. Can’t notice when it cuts in & don’t see any mpg difference when used or not. My previous Disco 2 TD5 was same….but with the Disco 1 with 300Tdi you could really feel the braking effect when air con was engaged……in fact I used to engage thé air on when going down long inclines to aid engine braking…even in cool weather ….I particularly remember Blue Bank near Whitby & A169 from Pickering……used to go there a lot……lots of engine braking saved brake wear. Had to remember to switch off aircon at bottom of hill….before a subsequent incline…..! FL2 SD4 HSE Lux Auto MY 2012— current
D2 TD5 HSE Man MY 1999 470kmls….gone 2014 ….lovely engine..chassis rotten
D1 300TDI Man MY 1996 56kmls….gone 1999…D2 much better
Wife’s FL1 1.8P MY 2001 32kmls …gone 2007…has Mini since.

Like others I leave ours on all the time. It's great in winter to stop condensation.

Previous car only had a 1.4 litre engine 44kW. We often turned it off at the lights for a "quicker" get away then back on. Also it worked well for mild engine braking down hills. It was used all the time & it was a really good AC.

Let's say for arguments sake that the AC has 6kW output, & it's a fairly inefficient at 300%. So input would be about 2kW.

As a percentage of the various Freelander engines power, it's pretty small.

Driving more comfortably & with clear windows to me has more safety value. Procrastination, mankind's greatest labour saving device!

Acoustic insulation ARB TPMS 3xARB air compressors After cooler Air tank On-board OCD pressure air/water cleaning Additional 50L fuel Carpet in doors ABE 2x1kg Waeco 28L modified fridge Battery 4x26ah Solar 120w Victron MPPT 100/20 DC-DC 18amps 175amp jumper plug Awning 6x255/60R18

Jimboland wrote:

Using air con will increase fuel consumption. Does anyone have any realistic/scientific idea about how much extra fuel air con uses?

Jimbo

Agree - turning off runs the risk of forgetting to turn it back on - and then drying out the seals and predisposing to nasty smells - which was when I noticed SWMBO had turned the AC off for some reason. Jules

The AC on our EV uses between 150 and 500 Watts of power depending on AC load, so would be similar for an ICE vehicle too.

A gallon of diesel contains 34 kWh of energy, so 500 Watts out of 34 kWh isn't much when viewed as a percentage, although the you have to remember that an engine is only 30% efficient.
From testing I've done on the Freelander, the AC reduction in economy is 2 or 3 MPG, while the system is working hard. So not really worth worrying about, and loosing say 5 to 10% efficiency, is definitely preferable to paying to have the AC repaired after it's been damaged by lack of use. Hyundai Ioniq 5 Ultimate. The family car.
2009 Rimini Red SE TD4. Gone.
2006 Tonga Green i6 HSE. Gone.
Audi A5 convertible, the daily driver.
1972 Hillman Avenger GT, the project.

On our 2018 trip in outback Australia because it was so dry & cool weather we did turn the AC off over a few tank fulls of fuel. To today I have every petrol receipt trip data reset every time. Just never put the entire history in a spreadsheet. But we did so for the outback trips.

We couldn't tell if we saved anything. Obviously we would have, but it was not worth the effort turning the AC off.

On our 2019 outback trip we left the AC on all the time.


The biggest issue is tail vs head wind. It went from 7.8L/100km to 12L/100km. A lot of long straight roads out there. Then we stopped for the day! We were not in a hurry.


Sydney city driving it's about 17L/100km. Lately about 20L/100km with too many very short trips. But then not using the car that much.


If one is stressing over AC, probably it's better to swap to 2 wheels with 33 gears! Procrastination, mankind's greatest labour saving device!

Acoustic insulation ARB TPMS 3xARB air compressors After cooler Air tank On-board OCD pressure air/water cleaning Additional 50L fuel Carpet in doors ABE 2x1kg Waeco 28L modified fridge Battery 4x26ah Solar 120w Victron MPPT 100/20 DC-DC 18amps 175amp jumper plug Awning 6x255/60R18

I have no idea what AC the Freelander is using. But it is probably a 5 cylinder variable compression system. So once the cabin is cool the AC is not working that hard.

The old AC were a fixed rate compression, so basically switched on & off. Probably stayed on most of the time. Procrastination, mankind's greatest labour saving device!

Acoustic insulation ARB TPMS 3xARB air compressors After cooler Air tank On-board OCD pressure air/water cleaning Additional 50L fuel Carpet in doors ABE 2x1kg Waeco 28L modified fridge Battery 4x26ah Solar 120w Victron MPPT 100/20 DC-DC 18amps 175amp jumper plug Awning 6x255/60R18

Lightwater wrote:

On our 2018 trip in outback Australia because it was so dry & cool weather we did turn the AC off over a few tank fulls of fuel. To today I have every petrol receipt trip data reset every time. Just never put the entire history in a spreadsheet. But we did so for the outback trips.

We couldn't tell if we saved anything. Obviously we would have, but it was not worth the effort turning the AC off.

On our 2019 outback trip we left the AC on all the time.


The biggest issue is tail vs head wind. It went from 7.8L/100km to 12L/100km. A lot of long straight roads out there. Then we stopped for the day! We were not in a hurry.


Sydney city driving it's about 17L/100km. Lately about 20L/100km with too many very short trips. But then not using the car that much.


If one is stressing over AC, probably it's better to swap to 2 wheels with 33 gears!

Nodge, with an EV where you can measure the use of power for the A/C, is the drive for the A/C direct from an electric motor or driven from a shaft in the drive train and can you use A/C stationary if a separate electric motor? I assume the A/C in an EV is more efficient but heating may not be as an ICE has on tap hot water that basically is free, the thermostat will close to keep the engine temperature at optimum my PC is slightly to the right of Genghis
2012 HSE SD4 In Orkney Grey now gone, best car ever.

Dartman the one wrote:

Nodge, with an EV where you can measure the use of power for the A/C, is the drive for the A/C direct from an electric motor or driven from a shaft in the drive train and can you use A/C stationary if a separate electric motor? I assume the A/C in an EV is more efficient but heating may not be as an ICE has on tap hot water that basically is free, the thermostat will close to keep the engine temperature at optimum

Thanks for all the interesting replies. I have done a couple of tank fulls with the aircon off and there appears to be no difference in MPG but as conditions and weather varied I couldn't draw any conclusions, so I will continue to keep the aircon on permanently as it makes for a more comfortable drive all year round.

Jimbo