Air conditioning and MPG

[RobertoMercini]

Question please - I know that having aircon on obviously affects fuel consumption but does anyone know whether thats affected by how high you have it on?

ie if the aircon is 'on', then its 'on' and the blowers just control how fast the cool air comes out, or does it use more fuel the higher you have the blowers?

 

[Rashman]

Question please - I know that having aircon on obviously affects fuel consumption but does anyone know whether thats affected by how high you have it on?

ie if the aircon is 'on', then its 'on' and the blowers just control how fast the cool air comes out, or does it use more fuel the higher you have the blowers?

I too have wondered this, but I believe the higher you have the AC set, the more fuel it uses.

Someone may correct me on that though.

Though, it's the slight loss in power that bothers me more than the slight increase in fuel consumption. lol

 

[killwilly]

Though, it's the slight loss in power that bothers me more than the slight increase in fuel consumption. lol

I've never noticed a loss of power in my last two cars, a BMW 320i and my current CLC 180. However, I did notice a considerable loss of power with the Nissan Primera I once had.

 

[Noobdelux]

drove 20 metric miles today and ended up with 6.6 pr 100 km, with ac on and a few passes thrown in : P

 

[Rashman]

I've never noticed a loss of power in my last two cars,....

Yeah, I actually agree.

....but I know the loss is there... and that's enough for me to dislike the AC.

 

[seymansey]

Quite noticeable in the C240, you can't quite rev it out as freely as when its off. That said, my aircon is broken and this isn't a issue

 

[flango]

Yeah, I actually agree.

....but I know the loss is there... and that's enough for me to dislike the AC.

Most cars turn the AC off when you give it full power so no power loss is experienced. Try a 3rd gear very sudden accelaration and see what happens, all our cars turn off AC automatically when driven in "Hurry up" mode.

 

[MarkJunedd]

Never noticed any significant increase in mpg with the aircon on, or any great loss is power for that matter.However it is a 3.2 V6 so if I was worried about fuel economy then I wouldnt have bought it. I do notice a slight blip to revs when first switched on but nothing to shout about.

 

[Privatedoc]

Think we are talking % here

All aircon will use energy, ones with engine driven compressors will cause energy consumption even when 'off' due to engine drag, albeit a tiny amount., some cars have true electric compressors that won't use energy when off.

A while back I had a Toyota aygo....3 cylinder 1 litre 58 bhp.....aircon knocked 5mph off the already poor top speed and 6 mpg off the average 55-60mpg. Large in percentage terms. Hence a nice big v8 probably wouldn't notice the difference but a smaller engine might.

But, I'd rather be cool, dry and comfy than worry about a pound or two come fill-up time

I'm putting the CAR in CARbon neutral. Ha ha!

 

[steve333]

Question please - I know that having aircon on obviously affects fuel consumption but does anyone know whether thats affected by how high you have it on?

ie if the aircon is 'on', then its 'on' and the blowers just control how fast the cool air comes out, or does it use more fuel the higher you have the blowers?

If you search the forum you will see this topic has been raised before,the general opinion being that the bigger the engine the less noticeable the power loss/mpg loss when a/c is activated

 

[Colin_b]

Aircon does affect fuel consumption. Less than having a window open, apparently.

 

[Supacool1]

Aircon does affect fuel consumption. Less than having a window open, apparently.

True. If you open the windows then it increases drag and effects the MPG futher than any Aircon load on the engine will.

 

[atlantictable]

I am in a good position to comment here. Most mercedes models, if not all, will have an engine driven AC compressor - the compressor being engaged by an electronic clutch, mechanically or electrically controlled. The compressor can use upto 12HP to drive. The systems will vary, but generally the compressor only turns on when needed, so the colder you have it the more it will be on. It should cycle every couple of minutes on average - more when hotter outside, less when colder. Cars with low gas or non functioning AC will not sap any power as the compressor will not engage. Some functions on the car heating system will engage the compressor continually. However the AC is used will affect both engine performance and fuel consumption - as long as it is functioning. However, the performance reduction is negligible (more noticeable on smaller engined cars) but the consumption could be reduced by as much as 8mpg depending on circumstances. A good tip is to ensure you use it at least once a month otherwise the seals on the compressor shaft can dry up and cause the refrigerant gas to leak - use it or lose it! Your in a merc so be cool

 

[timskemp]

True. If you open the windows then it increases drag and effects the MPG futher than any Aircon load on the engine will.

It will of course not affect the MPG at all in traffic, where the air conditioner has the biggest affect on fuel consumption.

The faster you're going, the more having a window open affects MPG and the less having the AC running affects MPG.

 

[SAFC]

Good post from Atlantictable.
Smaller cars I've hired in Italy use a great deal of fuel when the Air Con is taking a bashing.
Generally, the cooler you have the setting the more fuel you will use as the engine works harder to drive the compressor - assumng your car has a temperature setting control. If not then the faster you wind up the fan the more fuel you'll use.
I have to say the difference in fuel consumption over about 20 miles in my C270 CDI is negligible.

 

[renault12ts]

drove 20 metric miles today and ended up with 6.6 pr 100 km, with ac on and a few passes thrown in : P

What's a metric mile?

 

[SAFC]

Renault12ts,

About 1600 metres. It's what they say when they run 1600 metres in a race instead of 1 mile. Daft innit?

 

[Sonny Burnett]

this seems like such a silly thing to worry about. no offence but it just does, lifes to short to worry about AC and the 80p you may or may not save your self

lets be straight here a Mercedes is the last car you want to buy to save money... you should be looking at a yaris or similar seriously...

your time could be up tommorw and who wants to go out worrying about AC

 

[st13phil]

Most cars turn the AC off when you give it full power so no power loss is experienced. Try a 3rd gear very sudden accelaration and see what happens, all our cars turn off AC automatically when driven in "Hurry up" mode.

Back in the mid-eighties while on holiday in Canada I rented a Buick Skylark (horrible car, but that's a different story) and found very quickly that if I needed full power for an overtake it was essential to turn the AC off before I started the manouvre

 

[comports]

I seem to remember watching an episode of "Myth Busters" once when they tested this.

Two identical cars on an oval track. Both completely empty and then filled the same amount of fuel, driven at the same speed at the same time on opposite sides. I believe the result was the AC car lasted a bit longer then the windows open car but only by a very small margin.

This test of course only tested fuel economy and not power differences so slightly off topic...

As said above though - I drive a 3.2 V6 CLK and a 4.6 Range Rover so economy is not top priority for me..