[TMP]

ok...some interesting advice.

Still think it may impact fuel consumption, but get your points.

What abut when its cold though....below a certain temp(is it 3c) the compressor will not work anyway?

[shane55]

Yes when it's cold out, say 3 degrees, the heat load on the evaporator will be so small and the refrigerant flow reduced so much that it causes shutdown of the compressor by low refrigerant flow pressure. Either measure stops operation at low ambients where the outside air does the job of the compressor

[doughboy]

Exactly Shane55, well put indeed, you obviously know your dew points

You're right to say that modern climate controls are designed to be run all year round in full auto to do their job properly, and are as efficient as they can be at the same time.

By turning off the snowflake you're just hindering the system, maybe if you never use it then it will stay dry, but otherwise leave it on.

[HighlandPete]

I've tried both uses, leaving A/C (snowflake) on, and trying to run with A/C off and keep it dry in winter months. The second option takes some doing, as there are times when you just have to use A/C, to keep the car from misting. Get it wrong and you get caught out, adding moisture to the car, for the reasons Shane 55 has explained. So I just leave it on.

My E39 540i (like other older cars) was different, it would definitely switch itself off at about 4-degrees, so was a pain, as it could make misting a problem. So that was better to try and run dry, without A/C when the temperature was in in the lower range, where the A/C could be switching on and off in a single trip, and causing misting as you went along.

As to power/energy use, as said, it is not the same demand as when running on a hot summer day, flat out, to try and cool a red hot cabin. So minimal in the cooler months.

HighlandPete

[craig2859]

very interesting, I never knew this. A/C is going on permanent in the morning - cheers guys.

[chrismanchr]

I'll try running the a/c all the time also I'll take notice of how much more fuel it uses

I'll change the filter as well

as for having sex in the car , it ruins your seats! lol

[zltm089]

FACKIN HELL!!!!!!!!!!!!!!.....I never knew this!!!.....Even during the summer months, I was being "tight" and never put the A/C on!!!!!!


When I had my first car (vauxhall astra), if I put the aircon on, the car would lose so much power!!! ....and I remember when I was a child, my uncle used to switch the aircon off when overtaking!!!... always told me that aircon is bad, drinks petrol and makes the car slow!....


Will use A/C from now on...and keep an eye on fuel consumption....

[parapaul]

Originally Posted by zltm089

FACKIN HELL!!!!!!!!!!!!!!.....I never knew this!!!.....Even during the summer months, I was being "tight" and never put the A/C on!!!!!!

You bought a £40k, turbocharged 6-cyl 3 litre petrol car and you're being tight about aircon?

[AlanYoro35i]

Originally Posted by parapaul

You bought a £40k, turbocharged 6-cyl 3 litre petrol car and you're being tight about aircon?

Hahaha

[HighlandPete]

Originally Posted by zltm089

....and I remember when I was a child, my uncle used to switch the aircon off when overtaking!!!... always told me that aircon is bad, drinks petrol and makes the car slow!....

There is truth in that comment, older designs with fixed displacement would put high demands on an engine, and folks would notice the power drain, particularly if climbing hills.

Smaller engine cars still have that issue, to a degree, and at cruising speeds on a hot summer day, fuel consumption figures show a high % drop off in mpg when using A/C.

I remember a test where a VW Polo 1.4TDI was used to test the power drain on a small diesel. As the VW 1.4TDI (3-pot) was all about efficiency, it showed that at cruising speeds of something like 50mph the A/C required almost 40% more fuel on a hot day. It is not a simple equation of how A/C impinges on mpg. It involves percentages of HP needed to drive the cruising speed, against HP required to power the A/C, how that changes the road load. That can require quite a change in boost pressure on the engine at the same rpm, completely moving where it is on the BSFC map and resulting mpg.

Condensed, the bigger the engine, the less an A/C shows on consumption. (Smaller percentage change in parasitic losses).

HighlandPete

[chrismanchr]

I had a mk4 golf gti 1.8(it was quite slow) in the late 90's when you put the a/c on it virtually ground to a halt ,it couldnt run it lol my next car was my beloved e46 330ci ,i never noticed the a/c on at all ,loverly engine ,where as the e92 325i does lose a bit of power with the a/c on and driving around town it can be a problem ,I know flywheels etc have made a/c better ,but i'm still not sold on having the a/c on all the time

[doughboy]

Originally Posted by chrismanchr

I had a mk4 golf gti 1.8(it was quite slow) in the late 90's when you put the a/c on it virtually ground to a halt ,it couldnt run it lol my next car was my beloved e46 330ci ,i never noticed the a/c on at all ,loverly engine ,where as the e92 325i does lose a bit of power with the a/c on and driving around town it can be a problem ,I know flywheels etc have made a/c better ,but i'm still not sold on having the a/c on all the time

Chris, It causes confusion using the term 'A/C ON', that's not what the snowflake does.

All the snowflake button does is allow the car to use the compressor as it sees fit, in the winter it may be very little if at all some days, just a little for some dehumidifying probably.

The fact the compressor has variable output means the car can adjust the output level as required, only using max power on hot days after you've parked up for example.

Only on OLD cars does the term 'A/C ON' equate to a fixed output 100% full power AC systems (all or nothing).

I would say its better to leave it on ALL winter where power consumption is minimal, then maybe turn it off in the summer if you really want to save fuel.

I'd be amazed if you can feel the difference in car performance with it on or off.

[shane55]

In winter time when the cooling load in at it's absolute minimum the extra work the engine has in turning the compressor is almost unnoticeable because the compression ratio is very low. Put simply, the pressure difference between the suction and discharge side of the compressor is at its lowest, for example 2bar suction and 6bar discharge. This could be compared to inflating an empty balloon...pretty easy.

Now on the other hand in summer the work load will be triple even more than what it was in winter. Firstly the system will always have to start fully loaded...this means parked in the sun with the interior temperature in the 40's and the ambient in the 20's. In summer the compression ratio is much higher, as the system is trying to loose heat to the ambient which is much closer to the refrigerant temperature than in winter, the difference between suction and discharge pressure could be 20bar ... Now imagine yourself trying to inflate a balloon under water...not so easy eh!

Fully loaded in summer the system will consume 5 horsepower. As the interior cools down the required power needed to do the same job will fall this is somewhat due to ram air forced into the condenser at 60mph down a motorway....it's in this case the variable swash plate is great as the 5 hp demand curves off reducing fuel consumption significantly.

As said by Pete on a small car this is a lot but on a 200+hp car this is peanuts!

[will1968]

I've tried both leaving snowflake button on and off. But say I set my climate control to 22C (this time of year) with the snowflake button off this is fine, but with the button on it feels like the temp drops so have to turn climate control upto say 24C or 25C to be comfortable again.
Why is this or do I have a problem with climate control as for cooling in summer is fine.

[zltm089]

Originally Posted by parapaul

You bought a £40k, turbocharged 6-cyl 3 litre petrol car and you're being tight about aircon?

£20k second hand! ;-) have to save for that remap!...

[HighlandPete]

Originally Posted by will1968

I've tried both leaving snowflake button on and off. But say I set my climate control to 22C (this time of year) with the snowflake button off this is fine, but with the button on it feels like the temp drops so have to turn climate control upto say 24C or 25C to be comfortable again.
Why is this or do I have a problem with climate control as for cooling in summer is fine.

How do you run the vents? All fully open and left on full auto, (no preferred regions)?

I run mine at 19.5C (both zones) in summer or winter, and set the upper body/face level thumbwheel to get the right face temperature blends. Normally about mid position, this time of the year, with ambient temperatures in the 0 - 8C region. Hardly ever touch the temperature settings, as the system is designed to give the fastest warm up time, to any set temperature.

I'll run that temperature from about -5C to about 18C ambient. Above that I may up, yes, up the CC temperature, to say 21C, so as not to chill the car too much.

Used to do the same in the 540i, but that did change slightly when you had the snowflake button switched on or off.

HighlandPete

[shane55]

Originally Posted by HighlandPete

How do you run the vents? All fully open and left on full auto, (no preferred regions)?

I run mine at 19.5C (both zones) in summer or winter, and set the upper body/face level thumbwheel to get the right face temperature blends. Normally about mid position, this time of the year, with ambient temperatures in the 0 - 8C region. Hardly ever touch the temperature settings, as the system is designed to give the fastest warm up time, to any set temperature.

I'll run that temperature from about -5C to about 18C ambient. Above that I may up, yes, up the CC temperature, to say 21C, so as not to chill the car too much.

Used to do the same in the 540i, but that did change slightly when you had the snowflake button switched on or off.

HighlandPete

Pete how can you not have an even number on your climate control... I'm a bit mad on this one always have it set on evens

[HighlandPete]

Originally Posted by shane55

Pete how can you not have an even number on your climate control... I'm a bit mad on this one always have it set on evens

Now you are confusing me. Do I go up to 20C, or back to 19C, to make it tidy looking? One of each? Nah, that will look worse. I'll try 20C, but it may be too hot.

HighlandPete

[chrismanchr]

i run mine at 25 both sides at this time of year i like it hot that why i cant understand why it steams up

[doughboy]

Originally Posted by will1968

I've tried both leaving snowflake button on and off. But say I set my climate control to 22C (this time of year) with the snowflake button off this is fine, but with the button on it feels like the temp drops so have to turn climate control upto say 24C or 25C to be comfortable again.
Why is this or do I have a problem with climate control as for cooling in summer is fine.

Holy crap ice man! 25????

My shoes split and my eyelids stick to my eyeballs at 24, even with the snowflake on.

For best results, all vents need to be open, not blowing in your face, use the centre vent control to keep cooler air on your face.

[TMP]

Righto guys, I am getting convinced to run the aircon on both of the cars.

but, if somebody can tell me it will also make the compresser and aircon system last longer that should swing it.

oh, and half degree values are where the cool people chill at - 20.5c to be exact

[HighlandPete]

Originally Posted by chrismanchr

i run mine at 25 both sides at this time of year i like it hot that why i cant understand why it steams up

That is one high temperature. I do wonder if that actually adds to the problem, as it is a constant heat and cooling cycle, every day or twice a day, with a bigger temperature differential than most would have. Particularly as you are not dehumidifying it. You haven't got water ingress some place have you? That will really make it mist up at those temperatures, as it cools off.

Let a cold car and sit in the sun, in any sort of humidiy and what happens...? It steams up the car. Even a little bit of damp on the carpet mats will make a lot of misting. I've seen it happen, makes me panic as I think I've got water leaking into the car.

Do you get a chance to air the car? I'm serious... you can reduce moisture build up, with a couple of hours with doors open and air blowing through.

HighlandPete