[arhoads335i]

Anyone ever notice the AC turning on when you don't want it to?
I personally drive around with it off a lot because it ruins shifting. But it seems to come on even when the AC button is off. So I have to turn off the fans which I don't like to do.

[overcoil]

I hadn’t noticed...but wonder if it has to do with anti-fogging windshield feature

[albertw]

On mine, if I start the engine with the AC set to off it stays off. Once I turn the AC on I have found only two ways to turn it off and have it stay off - set the temperature setting to about two degrees above the outside temperature, or turn off and restart the engine. The first can be uncomfortable and the second can be inconvenient.

Were you following this forum during the air conditioning wars of about a year ago? If not, be warned that some people here can get pretty huffy when someone says they want the AC off. Many of them mod their cars endlessly but when it comes to AC "BMW engineers are omnipotent". The fact that the manual makes it clear that off and auto are both acceptable seems to make no difference to them.

I think the fact that BMW makes it so hard to keep the AC off simply means that the engineers think most people are too inattentive to dry out the HVAC properly after they use the AC, but no one really knows.

[morphomeman]

How does the AC ruin shifting? Just curious, though I don't shift anymore, at least consciously.
And how would I dry out the HVAC properly? I have owned half a dozen BMWs in the last 20 years and always leave the AC on auto all the time, the way God intended. None of them has had a problem with HVAC (yet!!).

[celsdogg]

I have had this occur too. I read somewhere recently that the F30 has a humidity sensor that turns on the AC regardless of the button. F22 is probably the same.

at the end of a long trip, I like to run the air on high with the AC off just to evacuate all the cold air. helps over the long term by keeping any condensation from forming. at least thats the theory.

this HVAC system is over complicated I think. E30 was perfect in ease of use, simplicity, and number of options. IMHO anyway.

engine speed changes when the AC is running. how fast it speeds up and slows down. gotta slightly change how fast or slow you shift. experienced MT driver's do it without thinking. cars these days have enough power where it barely noticeable. in lower powered cars like my E30, there is a huge difference.

yes, my E30 had AC, lol.

[TajoMan]

try to put HVAC on manual mode, direct the air flow to panel vent or floor vent only.
(No air directed to windshield)
Then turn off AC with AC button.

It should stay off this way.

Auto HVAC can run AC compressor for defog operation. (regardless of the AC on/off)

[smanoj77]

Same happens with my m240. I even coded the AC not to automatically come on in Auto mode, still it comes on even if the AC light is off. I notice it happens when I start the car up and shuts off after about 5min.

[Shovelman]

The 5 minute run on startup sounds right. This would dry out the ducts and coils. This is probably a misguided nanny.

Not all the world is as humid as the Fatherland.

[bimmerfile]

Air con definitely will come on by itself in these cars.
Case in point: Last week was pretty nice (weather-wise), so the top was down and therefor no need for the air con. Saturday I had to go into Toronto on an errand and it was cool but misty and rainy. 10 minutes into my drive, I felt cold air hitting my face - the air con had come on by itself. The windows weren't fogged up, but I assume the air con sensors must had hit some humidity threshold.
The air con stayed on for the remainder of the trip.
BTW, no lights showed up which would indicate that the air con was on.

[35mmSummicron]

A work around for me is to let the AC run for a good couple minutes, then turn it off manually.

I'm guessing once the AC is engaged it may need to run a few cycles before the system can manually shutting down.

[arhoads335i]

So must be a humidity thing. Glad I'm not the only one going crazy

[Julie Silver]

I guess it suppose to be a software issue of AC control board?

[Poochie]

Apparently, this is the new normal; it happen to me in a brand new X2 loaner, It didn't freak me out, it seems like it had a purpose..

There is similar thread in the M4 forum:

Fan still on for few minutes after ignition is turned off https://f80.bimmerpost.com/forums/sh....php?t=1614290

[blue_beast335]

Hi all,

Thanks a lot to all of you.. God i`ve searched for this for some time...
I have an F30 335dx and from time to time, especially when it rains.. the AC turns on by itself while the AC button is off..

It driven me crazy..i thought it was something with the AC compressor.. and when i saw the price from BMW.. omg )

Thanks!

[Shovelman]

So if we can buy a tune for the engine, how about one for the HVAC?

[Kernel Kurtz]

The AC is not just to cool the air, it also functions as a dehumidifier. My AC runs all winter long, even (especially) when it is -30C out. The AC dries the air, and the heater heats it. Keeps the windows from fogging up. Many years ago I operated a truck plow and air conditioning was a huge benefit in keeping the windows clear.

[XutvJet]

Originally Posted by Kernel Kurtz

The AC is not just to cool the air, it also functions as a dehumidifier. My AC runs all winter long, even (especially) when it is -30C out. The AC dries the air, and the heater heats it. Keeps the windows from fogging up. Many years ago I operated a truck plow and air conditioning was a huge benefit in keeping the windows clear.

^ This. The intent is to also keep the HVAC duct work dry and free of mold.

[albertw]

Originally Posted by Kernel Kurtz

The AC is not just to cool the air, it also functions as a dehumidifier. My AC runs all winter long, even (especially) when it is -30C out. The AC dries the air, and the heater heats it. Keeps the windows from fogging up. Many years ago I operated a truck plow and air conditioning was a huge benefit in keeping the windows clear.

Air at -30 can hold almost no moisture. Heat it up to a comfortable temperature and the relative humidity will be well below 40%. Most of the moisture in the car at -30 comes from your breath. It's the warm air directed at the windshield and side windows that removes the interior frost, not the fact that the air conditioner is on. It would be much more efficient if the air could be heated to a much higher temperature, but sadly most manufacturers insist on turning on AC when the air distribution is set to blow air at the windows. As a result the air is nowhere near as warm as it could be. This also negatively affects how well exterior frost is removed, because that only happens when the windows are heated.

[Kernel Kurtz]

Originally Posted by albertw

Air at -30 can hold almost no moisture. Heat it up to a comfortable temperature and the relative humidity will be well below 40%. Most of the moisture in the car at -30 comes from your breath. It's the warm air directed at the windshield and side windows that removes the interior frost, not the fact that the air conditioner is on. It would be much more efficient if the air could be heated to a much higher temperature, but sadly most manufacturers insist on turning on AC when the air distribution is set to blow air at the windows. As a result the air is nowhere near as warm as it could be. This also negatively affects how well exterior frost is removed, because that only happens when the windows are heated.

Breathing is absolutely a big moisture source, and since the air can't hold it it will condense wherever it can. Heating the windows removes the frost from that surface, but the water does not disappear, it will just condense elsewhere in the car unless it is removed. You can remove that moisture in two ways, either condense it out with the AC, or replace the inside air with (hopefully dry) outside air frequently.

People smarter than me have decided the former is a better solution, and given interior fogging is pretty much a thing of the past I'm gonna defer to them on that. The latter is how we did it in the old days. Nothing like driving in the winter with your window open.

[albertw]

Originally Posted by Kernel Kurtz

Breathing is absolutely a big moisture source, and since the air can't hold it it will condense wherever it can. Heating the windows removes the frost from that surface, but the water does not disappear, it will just condense elsewhere in the car unless it is removed. You can remove that moisture in two ways, either condense it out with the AC, or replace the inside air with (hopefully dry) outside air frequently.

People smarter than me have decided the former is a better solution, and given interior fogging is pretty much a thing of the past I'm gonna defer to them on that, cause the latter is how we did it in the old days. Nothing like driving in the winter with your window open.

Moisture from your breath condenses on the windows because they are colder than everything else inside the car once you've had the heater running awhile, not because "the air can't hold it". Only the air right up against the windows is cooled enough that it can't hold it. Flowing warm air against the windows warms both the cold surface layer and the windows, which is why it prevents condensation.

Running the AC will remove the moisture your breath puts into the air only on recirculation. Try that at -30 and see how clear your windows stay.

Have you driven in -30 recently? The only thing some modern cars do better is aim some warm air at the side windows. (And, of course, running the AC just makes that less efficient.)

The proportion of cars that are driven routinely at very cold temperatures is so low that engineers don't bother to design the cars to work well then. If they did they would add a button that would turn the AC off. But that would cause far too many problems in humid, warm climates.

[Kernel Kurtz]

Originally Posted by albertw

Moisture from your breath condenses on the windows because they are colder than everything else inside the car once you've had the heater running awhile, not because "the air can't hold it". Only the air right up against the windows is cooled enough that it can't hold it. Flowing warm air against the windows warms both the cold surface layer and the windows, which is why it prevents condensation.

Running the AC will remove the moisture your breath puts into the air only on recirculation. Try that at -30 and see how clear your windows stay.

Have you driven in -30 recently? The only thing some modern cars do better is aim some warm air at the side windows. (And, of course, running the AC just makes that less efficient.)

The proportion of cars that are driven routinely at very cold temperatures is so low that engineers don't bother to design the cars to work well then. If they did they would add a button that would turn the AC off. But that would cause far too many problems in humid, warm climates.

Moisture from your breath (or anywhere else) condenses on the coldest places unless/until the air can hold it. This is simple chemistry, the water molecules do not magically disappear if you heat them.

If I had to choose between recirc with AC or recirc without AC, that is a no brainer of course. I prefer no recirc and AC, that works the best almost always. Perhaps you could try it and report back.

And I drive in -30 every winter. I'm quite sure the reason there in no AC off button is not because I don't live in a warm climate and the engineers don't care. We have hot weather and cold weather packages on these cars that encompass many mechanical systems. Pretty sure the button would be easy if it offered any benefit.

[albertw]

Originally Posted by Kernel Kurtz

Moisture from your breath (or anywhere else) condenses on the coldest places unless/until the air can hold it. This is simple chemistry, the water molecules do not magically disappear if you heat them.

If I had to choose between recirc with AC or recirc without AC, that is a no brainer of course. I prefer no recirc and AC, that works the best almost always. Perhaps you could try it and report back.

It seems to have escaped your attention that on regular AC all the air the system blows comes from outdoors. Only on recirculation can the AC remove moisture from the air already inside the car. And, as you have acutely observed, that doesn't work very well, which was my original point.

As for your understanding of "simple chemistry" (actually it's basic physics), all I can say is WOW! I bow down before a master of self deception.