Aircon on effect tuning?

[flybobbie]

After discussion elsewhere on this board about switching ignition on for 10 seconds.
Did that few days ago i noticed the engine could rev with ease to 7000rpm and 60 in second.
Felt it could go past without too much effort. Not sure if there is a rev limiter.

Today had to go out for another replacement windshield and driving back the car seem to have more power.(Must windshield effect).
Then got home noticed i had left the aircon on low.
I wonder if the car tuning changes to compensate for aircon on?
Usually fans start to run, wonder if temperatures are different.
I noticed it running just below 120, not that warm today.

 

[flybobbie]

Could be more load on engine, engine getting hotter, running more optimum for the current ambient conditions.
I rarely see temp. just below 120 unless we have heatwave in traffic.
Temp. today about 14 c.

 

[Anonymous]

What chassis /engine was this?

 

[Rockhopper]

Every car I’ve ever driven (including my Z4) runs much better with the AC off as it’s takes significant engine power to turn the compressor.

 

[Anonymous]

So most stats state 10 ft lb ish and 10 bhp for non BMW engines..can't see why it would be much different for BMWs..

 

[flybobbie]

23i.

 

[Pondrew]

I don't think there is an "air con on" engine map TBH. The only thing it does do is increase the idle speed when you press the a/c button to stop the engine stalling at idle cos a ferkin great compressor is instantly drawing a big load, as well as a dirty great big electric fan being started at the same time.
I would check your cooling fan, or debris in the a/c condenser and oil cooler if it's running hot with the a/c on. I can't tell from just looking whether the a/c condenser is in front of the rad but that is normally the case on cars. If the fan isn't running on low speed, all the heat from the oil cooler, then a/c condenser will have to pass through the rad without forced assistance. A/c condensers kick out a lot of heat and can cycle on their HP switches without any warnings showing.

 

[Pondrew]

So most stats state 10 ft lb ish and 10 bhp for non BMW engines..can't see why it would be much different for BMWs..

The old adage was "an a/c compressor uses 10% of engine power and uses 10% more fuel" but that was when an average ICE made 90bhp at 6000 rpm.
It's pertinent to remember that the compressor is directly driven off the crank belt. It will run at the same speed as the belt. They cycle constantly when driving, usually controlled by pressure switches for the refrigerant; LP and HP (this is all assuming there has not been a massive change in the technology of vehicle a/c compressors in the last 20 years, which I doubt).

 

[flybobbie]

I will check all this week the effect of running with and without ac on low.

 

[mcbutler]

Find a level stretch of road and set your 'instant fuel consumption' in the display.
Do a run with AC off and another with it on.
Then another turning it on half way through the run.
The amount of fuel it uses is surprising, especially when you first turn it on and its working hard to cool the car interior.

I rarely use it (tight northener) but I do switich it on once a month for a few minutes, this keeps the refrigerant and lubricant circulating and all the internal seals etc lubricated.

 

[tomscott]

If you've got the top down there's no need for aircon

 

[flybobbie]

If you've got the top down there's no need for aircon

Yes there is, if it's very warm nice to have cool breeze from the vents.

Just don't use it in winter to demist, did that once in a MR2.
Within seconds of switching off, the whole screen misted over, couldn't see out.

 

[flybobbie]

Find a level stretch of road and set your 'instant fuel consumption' in the display.
Do a run with AC off and another with it on.
Then another turning it on half way through the run.
The amount of fuel it uses is surprising, especially when you first turn it on and its working hard to cool the car interior.

I rarely use it (tight northener) but I do switich it on once a month for a few minutes, this keeps the refrigerant and lubricant circulating and all the internal seals etc lubricated.

My point in a way, the higher fuel consumption brings the engine temperature up to it's optimum.
Normally my daily 7 mile drive to work never gets it up to ideal running temp., aircon on might speed that up, then switch off.

 

[mcbutler]

Find a level stretch of road and set your 'instant fuel consumption' in the display.
Do a run with AC off and another with it on.
Then another turning it on half way through the run.
The amount of fuel it uses is surprising, especially when you first turn it on and its working hard to cool the car interior.

I rarely use it (tight northener) but I do switich it on once a month for a few minutes, this keeps the refrigerant and lubricant circulating and all the internal seals etc lubricated.

My point in a way, the higher fuel consumption brings the engine temperature up to it's optimum.
Normally my daily 7 mile drive to work never gets it up to ideal running temp., aircon on might speed that up, then switch off.

I dont think it would make that much difference to be honest, best thing is to just try it I guess..

 

[Pondrew]

My point in a way, the higher fuel consumption brings the engine temperature up to it's optimum.
Normally my daily 7 mile drive to work never gets it up to ideal running temp., aircon on might speed that up, then switch off.

Let me get this right. You think that driving your 7 miles with the a/c on will help your engine? Seriously?
It will only put the engine under more load when it's cold and use more fuel.
There is a reason why BMW started fitting oil temp gauges instead of the normal water temp ones.

 

[Marcoose]

I feel my cars have far more pep after I eat a can of beans. Even more if I add a couple of hard boiled eggs.

 

[flybobbie]

I think there is barely any load, at idle the rpm needle hardly budgies from normal tickover.
Cold air flowing out so pump clutch must have pulled in.
Only jumps a touch as you switch the air con off, probably as fan cuts out.
I'm quite sure in warmer climates folks would start a journey with the aircon on.

 

[mcbutler]

My point in a way, the higher fuel consumption brings the engine temperature up to it's optimum.
Normally my daily 7 mile drive to work never gets it up to ideal running temp., aircon on might speed that up, then switch off.

Let me get this right. You think that driving your 7 miles with the a/c on will help your engine? Seriously?
It will only put the engine under more load when it's cold and use more fuel.
There is a reason why BMW started fitting oil temp gauges instead of the normal water temp ones.

Thats odd, your post quotes me as making flybobbies statement!

 

[flybobbie]

Well can effect performance. If the aircon rad is in front of the engine rad. the engine rad will be warmed by air con rad.
By the time the engine thermostat opens to let cooler rad. water in it's already warmed up by the air con rad.
On a cool day with cabin heat on the engine might never reach it's optimum temp. on shortish journeys.
Shutting cabin heat off and running aircon might speed temp. rise up to optimum.

 

[Anonymous]

I think there is barely any load, at idle the rpm needle hardly budgies from normal tickover.
Cold air flowing out so pump clutch must have pulled in.
Only jumps a touch as you switch the air con off, probably as fan cuts out.
I'm quite sure in warmer climates folks would start a journey with the aircon on.

AFAIK the idle is controlled by the ECU..it maintains a constant rpm despite changing accessories loads..so a/c or alternator cycling shouldn’t affect idle speed