How does Climate Control affect MPG?

Firestar_3x · 1 Dec 2009 at 10:33

gurusan said:
Yeah but I'm pretty sure most if not all modern cars will disengage the AC compressor via a clutch at WOT. My old 93 civic did.

True, but i'm not sure if its only on WOT or on a engine load basis.

gurusan · 1 Dec 2009 at 10:39

True, me neither.

john_s · 1 Dec 2009 at 10:59

Orange Peel said:
Couldn't tell you if it affects MPG as I've not had it off long enough to notice.

05 Mondeo Zetec 2.0 Oil Burner.

"Yeah that!"

Mine's an 04 plate though.

Don't notice when it kicks the compressor in either, whereas on my mk 1 Mondeo V6, the compressor would come in with a clunk, and it noticeably sapped power.

jamoor · 1 Dec 2009 at 11:03

it shouldnt make a difference on any car worth owning.

Jonnycoupe · 1 Dec 2009 at 22:14

Talking 25mpg drop here at 60mph.

Scania · 2 Dec 2009 at 03:33

[TW]Fox;15427181 said:
Big as in big. A 1.4 litre engine is not big. 2.5+.

With my Scania (12 Litre in-line 6) the difference is under 0.5 MPG. (Totally un-scientific, merely what I have deduced playing around with my Aircon & fuel computer!)

gurusan · 2 Dec 2009 at 08:45

lol @ people calling 1.4 big. Big to me is 4.0+

the 12 liter guy above wins though :/

mrk · 2 Dec 2009 at 09:03

Mine is 2litres only yet CC+AC is on every time and with it off MPG doesn't shift much at all.

What does make my MPG go from 39 to 24 however is damn traffic and my lack of a desire to eco-drive much these days ¬_¬

MikeHiow · 2 Dec 2009 at 09:45

I don't think it makes a blind bit of difference in my 1.6 Turbo.

Mine is on most of the time, even in the winter (helps keep the windows clear), however, it was broken for a few weeks at the end of the summer, I noticed no real difference in fuel economy. I'd be surprised if it makes much more than 1MPG difference on my car.

Jez · 2 Dec 2009 at 09:52

R420LA6X2/4MNA said:
With my Scania (12 Litre in-line 6) the difference is under 0.5 MPG. (Totally un-scientific, merely what I have deduced playing around with my Aircon & fuel computer!)

Very surprised that it makes anything like as much difference as that, what does 0.5mpg represent in terms of total %'age on a tractor like that? Must be a fair bit?

izzy eckerslike · 2 Dec 2009 at 09:53

I thought the main factor was whether the compressor was belt driven or the more eco electric compressor version, in the same way that cooling fans were originally belt driven the electric radiator fan improved engine efficiency considerably

Jez · 2 Dec 2009 at 09:55

izzy eckerslike said:
I thought the main factor was whether the compressor was belt driven or the more eco electric compressor version, in the same way that cooling fans were originally belt driven the electric radiator fan improved engine efficiency considerably

Usually even a belt driven compressor will have a clutch to engage and disengage it. I could see how if it was engaged perminently this would be the case but otherwise? :confused:

izzy eckerslike · 2 Dec 2009 at 10:03

Jez said:
Usually even a belt driven compressor will have a clutch to engage and disengage it. I could see how if it was engaged perminently this would be the case but otherwise?

An electric compressor makes little or no drag on the engine - only the battery, no clutch required either so it's got to be the better option

Firestar_3x · 2 Dec 2009 at 10:05

Depends on the efficiency of both systems, an electic compressor will simply but more load on the alternator which in turn puts more load on the engine.

Jez · 2 Dec 2009 at 10:07

izzy eckerslike said:
An electric compressor makes little or no drag on the engine - only the battery, no clutch required either so it's got to be the better option

An electric compressor will have a fairly meaty power draw though putting excess load onto the alternator, i cannot see it really being much different?

izzy eckerslike · 2 Dec 2009 at 10:10

Firestar_3x said:
Depends on the efficiency of both systems, an electic compressor will simply but more load on the alternator which in turn puts more load on the engine.

I've never understood that part about the alternator affecting the engine efficiency with extra load as it's constantly belt driven anyway

div0 · 2 Dec 2009 at 10:19

I've never turned mine off to notice. Can't imagine it would be much though.

Firestar_3x · 2 Dec 2009 at 10:24

izzy eckerslike said:
I've never understood that part about the alternator affecting the engine efficiency with extra load as it's constantly belt driven anyway

My understanding is a larger electrical load on the alternator means a bigger force trying to stop the alternator from spinning, so the engine is required to put more physical power into the alternator to stop it from stalling under the electrical load demand.

But i'm happy to be corrected if this is wrong.

BigglesPiP · 2 Dec 2009 at 10:25

Makes a difference on a 1.3 Proton Wira.

Firestar_3x · 2 Dec 2009 at 10:26

Turning the indicator on probably makes a mpg difference to that pile of junk.