[3Si]

Anyone experiencing this? Is this a feature that it takes awhile for the AC to shut off after pressing off the AC button? It's been like this since day 1.

[Whatup]

I've noticed the same thing, where it's still blowing cold air for a few minutes. Can't tell you why though.

[Aronis]

The A/C in the M2 is actually very nice as it appears actually to have more capacity than the car needs. So when you turn off the compressor, the condenser is still pretty cold. You'll have cold air coming out of the vents until the condenser heats back up again.

Mike

[ClothSeats]

I thought this is a feature to prevent moisture buildup in the compressor.

[Tralfaz]

At some point I was planning to post something about the same issue. I will turn off the AC and keep looking over to make sure the auto and AC lights are actually off when it keeps blowing cold air.

[greasypeanut]

I've even noticed my a/c being cold the next morning. Shocking as it's summertime and my insulated garage where my water heater is also located keeps heat in very well.

[3Si]

Glad I'm not the only one then. Doesn't really bother me. I've noticed that it also depends on the temperature outside. If it's really hot outside, it shuts down sooner, guess that has to do with the condenser being used more to keep the temp low.

[XutvJet]

Originally Posted by ClothSeats

I thought this is a feature to prevent moisture buildup in the compressor.

That's exactly right. It also is done to dry out the HVAC piping to reduce mold.

[MerlinPurple]

Originally Posted by ClothSeats

I thought this is a feature to prevent moisture buildup in the compressor.

Originally Posted by XutvJet

That's exactly right. It also is done to dry out the HVAC piping to reduce mold.

+1 ... be thankful it stays on to dry the evaporator.

Nothing worse than the smell of 'moldy' air blowing out the vents. E46M suffered from this issue (no drying) and once the mold is in it's very hard to remove.

[Bluenose-2er]

Thanks for this post! I was wondering what the heck was going on. Now I can save myself a stupid question at my next service.

[ZPrime]

Drying feature sounds awesome. On my Audi, off is off... So I manually turn off A/C (while leaving the climate still on Auto) to clear everything out. Not having to deal with this and just being able to turn it "off" and allow the car to handle the rest...

To clarify - this is happening when you fully shut off the climate control, right? Not just "after pressing A/C button but hvac system still 'on'"?

Otherwise... it's not a "feature" at all, it's just how car HVAC systems work. The A/C evaporator is just part of the airflow path. If it's cold still, you'll still get cold air as long as the blower is on, even if you've "turned off" the A/C portion. You're just turning off the compressor, that's it.

[pruettfan]

You have two knobs that control the temp on each side of the car, if you don't want the residual cold from the AC simply turn those knobs to the temp you want. My guess is in every case they are set to 60 degrees so there is no reason for the system to not provide residual cooling from the system after the compressor stops being engaged. Most of us, myself included are using our AC as on and off more so than setting the temp as it was designed to be used. Of course I live in AZ so when we use AC its always going to be full blast.

[bernstem]

Why would you ever turn it off? Just set the temp where you want it and let the computer figure out the ventilation. It will automatically adjust temperature, fan speed and which vents to use for optimal comfort. Even if the car is the temp you want, a bit of air circulation will keep it more comfortable.

[Bluenose-2er]

Originally Posted by bernstem

Why would you ever turn it off? Just set the temp where you want it and let the computer figure out the ventilation. It will automatically adjust temperature, fan speed and which vents to use for optimal comfort. Even if the car is the temp you want, a bit of air circulation will keep it more comfortable.

Because the A/C is a drag on power and decreases mileage... and the "Auto" system is not very smart in only using A/C when it needs cooling. On most cars I have used (owned or rented) the "Auto" means it uses a varying combination of A/C and heating (often at the same time) to achieve the set temperature... and it has to be really cool for it not to engage the A/C at all.

I also avoid the "Auto" setting on really hot or cold days, because it sets the fan into 'jet take off' mode to try and catch up in as little time as possible. I can wait a few minutes more and avoid the feeling of being in a wind tunnel thank you.

[Cibbersicks]

I personally find my AC too cold here in the U.K. We might have had 3 days this year where it's been over 30deg C outside and I've had it on full blast, apart from then generally I don't have it on. For example today it's 19degC so I tried to match the interior temp with outside, and it just started pumping icy cold air inside.

Then I also have the issue with fogging the bottom of the windscreen. My Gf's 118d does the same, in the exact same pattern, it's so annoying...

[V.Smurf]

Hi Folks,

Originally Posted by Bluenose-2er

... and the "Auto" system is not very smart in only using A/C when it needs cooling. On most cars I have used (owned or rented) the "Auto" means it uses a varying combination of A/C and heating (often at the same time) to achieve the set temperature... and it has to be really cool for it not to engage the A/C at all.

There is a common misconception that A/C = cooling.

Air Conditioning is a heat exchange system, that also removes moisture from the air. It is therefore very good at keeping the glass (particularly that on the windscreen) from fogging in cold weather.

Temperature control runs independently of the A/C function ... so you could quite appropriately run the A/C while heating up the car. Everyone gets that A/C = cooling, but it will just as easily perform the heating function ... and running the heater with the A/C function on is a perfectly sensible thing to do if it is cold!

Hope this helps

Cheers,

[Bluenose-2er]

Originally Posted by V.Smurf

Hi Folks,

There is a common misconception that A/C = cooling.

If it were a heat pump, I would agree. But auto a/c is not that sophisticated. It is cooling only. Yes, it engages to dehumidify, as that is a thermodynamic effect of the a/c process. But it does not stop cooling. It just compensates with heat as well when it is being used to dehumidify.

[bernstem]

Originally Posted by Bluenose-2er

Because the A/C is a drag on power and decreases mileage... and the "Auto" system is not very smart in only using A/C when it needs cooling. On most cars I have used (owned or rented) the "Auto" means it uses a varying combination of A/C and heating (often at the same time) to achieve the set temperature... and it has to be really cool for it not to engage the A/C at all.

I also avoid the "Auto" setting on really hot or cold days, because it sets the fan into 'jet take off' mode to try and catch up in as little time as possible. I can wait a few minutes more and avoid the feeling of being in a wind tunnel thank you.

I'm not terribly worried about the fraction decrease in MPG. If I was, I wouldn't drive an M car.

As for using A/C when the car doesn't need cooling, the system does that to dehumidify the air. If it didn't run, the windows would fog much more often - especially on a humid, cool day.

As for personal preferences, everyone is different. It is all good.

[Bluenose-2er]

Originally Posted by bernstem

I'm not terribly worried about the fraction decrease in MPG. If I was, I wouldn't drive an M car.

As for using A/C when the car doesn't need cooling, the system does that to dehumidify the air. If it didn't run, the windows would fog much more often - especially on a humid, cool day.

As for personal preferences, everyone is different. It is all good.

Yup, personal preference... I just stated my reasons to not leave it on all the time. Overlying reason being I am a control freak and like to micromanage my car If I let it control everything, it will eventually figure out it doesn't need me and the revolution will begin.

[BMWM5NYC]

Originally Posted by Aronis

The A/C in the M2 is actually very nice as it appears actually to have more capacity than the car needs. So when you turn off the compressor, the condenser is still pretty cold. You'll have cold air coming out of the vents until the condenser heats back up again.

Mike

Evaporator is cold. Condensor transfers heat outside of the car. It is warm.

[V.Smurf]

Hiya Bluenose,

Originally Posted by Bluenose-2er

If it were a heat pump, I would agree. But auto a/c is not that sophisticated. It is cooling only. Yes, it engages to dehumidify, as that is a thermodynamic effect of the a/c process. But it does not stop cooling. It just compensates with heat as well when it is being used to dehumidify.

I don't believe that to be correct: reverse cycle air-conditioners (which is a fancy way of saying those that heat & cool) perform both. And that's been the case for a very long time, even in automobiles.

Wiki has an article on it ... the heating part of aircon has been around for a very long time. I recall my dad (an engineer & pedant) in the early 1980's going on about the way the aircon system worked and how it could be used for both heating and cooling in equally efficient terms

And back on topic, the air-con running for a few minutes after being turned off would definitely assist in removing any moisture in the system ... regardless of whether the heater or cooling function was engaged at the time the "off" button was pressed.

Cheers!

[rwalker]

Originally Posted by V.Smurf

Hiya Bluenose,

I don't believe that to be correct: reverse cycle air-conditioners (which is a fancy way of saying those that heat & cool) perform both. And that's been the case for a very long time, even in automobiles.

Wiki has an article on it ... the heating part of aircon has been around for a very long time. I recall my dad (an engineer & pedant) in the early 1980's going on about the way the aircon system worked and how it could be used for both heating and cooling in equally efficient terms

And back on topic, the air-con running for a few minutes after being turned off would definitely assist in removing any moisture in the system ... regardless of whether the heater or cooling function was engaged at the time the "off" button was pressed.

Cheers!

Heat in our cars comes from an engine coolant heat exchanger in the dash.

A/C in our cars is not a reversible heat pump.

It is hugely wasteful to run a pump with engine power when there's a big pile of heat available from running the engine.

http://www.realoem.com/bmw/enUS/part...7-BMW-M2&mg=64

Note in the "lines" section:

http://www.realoem.com/bmw/enUS/show...diagId=64_1924

The lines running from the compressor only go one way: hot/pressure side to the condenser (outside the car), cold/suction side from the evaporator (inside the car).