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      07-16-2012, 09:34 PM   #1
2012_135i
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A/C on vs. A/C off

I'm surprised at the difference in performance when running the A/C as opposed to when it's off. Naturally there's going to be a difference, but the degree of difference is what I'm surprised at. All my previous vehicles were 4 cylinders that suffered a notable power drag with the A/C on. I figured the BMW's much more powerful turbo inline 6 would mitigate this, not completely, but at least to where it wouldn't be all that noticeable. Well, it's really noticeable. With the A/C off the car is alive, eager, and ready to rumble. With the A/C on it feels like driving through molasses, at least when starting off and getting up to speed. Anybody else notice this?
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      07-16-2012, 09:38 PM   #2
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Quote:
Originally Posted by 2012_135i View Post
I'm surprised at the difference in performance when running the A/C as opposed to when it's off. Naturally there's going to be a difference, but the degree of difference is what I'm surprised at. All my previous vehicles were 4 cylinders that suffered a notable power drag with the A/C on. I figured the BMW's much more powerful turbo inline 6 would mitigate this, not completely, but at least to where it wouldn't be all that noticeable. Well, it's really noticeable. With the A/C off the car is alive, eager, and ready to rumble. With the A/C on it feels like driving through molasses, at least when starting off and getting up to speed. Anybody else notice this?
Have not noticed that at all, I also thought the car has an electric AC, which should be less noticeable since it has the battery as a buffer. My rpm never goes down if the AC kicks in.
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      07-16-2012, 09:44 PM   #3
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AC on the one series is via an engine powered compressor. AC on, cool, AC off hot. In Houston, AC off in the summer is usually insufferable. Wait for the cool weather for that extra bit of force.
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      07-16-2012, 09:56 PM   #4
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I don't notice much difference at all with the A/C on.
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      07-16-2012, 10:22 PM   #5
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no power loss felt here at all...
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      07-16-2012, 10:25 PM   #6
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I drive my car like a newb with the ac on. Especially on the 1-2 shift the rpms drop so fast I always screw it up. I dont drive with any climate control on most of the time only when I have other people in the car and they always comment how "jerky" I am with the car.
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      07-16-2012, 10:51 PM   #7
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Originally Posted by FactorX81 View Post
they always comment how "jerky" I am with the car.
Tell 'em they can walk to their destination next time and see how jerky that is.
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      07-16-2012, 10:56 PM   #8
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I usually shift at higher RPM when the A/C is on to eliminate the jerk. Around 3500 to 4000 and rev match during DD.
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      07-16-2012, 11:51 PM   #9
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I get slightly better gas mileage with the A/C off. The 135i seems a bit more peppy too.
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      07-17-2012, 12:05 AM   #10
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Slightly less balls, but barely noticeable
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      07-17-2012, 12:17 AM   #11
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Haven't noticed a difference but then again I drive with the a/c 98% of the time. Here in Texas you can get away without a/c for one or two months a year tops.
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      07-17-2012, 12:29 AM   #12
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Try driving @ a constant speed and turn the a/c on? Watch the rpm..
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      07-17-2012, 12:40 AM   #13
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Quote:
Originally Posted by Section147
Slightly less balls, but barely noticeable
This. I notice it right away, but the difference isn't that great. Fwiw, mine is a dct
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      07-17-2012, 02:51 AM   #14
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I live in New Mexico and I can tell you in the 128 with a manual it is very noticeable. So much so I have to change my driving style if the AC is on. Shift higher, let the clutch out a bit slower. If not it will jerk
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      07-17-2012, 07:30 AM   #15
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I was noticing on my 135 that the AC doesn't make much of a difference, unlike most cars I've owned
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      07-17-2012, 02:18 PM   #16
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I don't drive my 128i manual any different with the AC on. I sometimes notice it is on but usually I don't. The compressor is kicking on and off once you get cooled down so even when it is "on" the clutch on the compressor may not be engaged so you may not be losing power. The AC in my bimmer does not cool my vert off as quickly as the AC in my Suzuki SUV, however, it seems a little undersized.

I also believe if you floor it the compressor gets disengaged. An instructor at the Performance Center said it is automatically disengaged when you are above 80% throttle (this was in a M school and we were above 80% throttle a lot).

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      07-17-2012, 02:29 PM   #17
2012_135i
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Lots of you seem to be experiencing a jerkiness with A/C on. I have a manual and haven't noticed that. I also don't notice much of a drop in RPM, but I haven't focused on that. I'll check it driving home today. Mostly what I notice is that it just seems to take more effort to get performance out of the car starting off and getting up to speed with A/C on - more pedal and noise but not a lot happening. The turbo doesn't feel as strong either. I really enjoy driving the car with A/C off, not near as much with A/C on, and sometimes it disappoints. I'm wondering if all the issues about DME programming (or reprogramming as the case may be) that are common topics on this forum factor in here. I took delivery of my 2012 car in December 2011 and have no idea what iteration of DME programming I've got, but I've wondered if it's giving me the full power and performance this car is supposed to have.
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      07-17-2012, 02:40 PM   #18
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Quote:
Originally Posted by FactorX81 View Post
I drive my car like a newb with the ac on. Especially on the 1-2 shift the rpms drop so fast I always screw it up. I dont drive with any climate control on most of the time only when I have other people in the car and they always comment how "jerky" I am with the car.
CDV delete; nothing to do with A/C
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      07-17-2012, 03:22 PM   #19
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Quote:
Originally Posted by avecta View Post
Try driving @ a constant speed and turn the a/c on? Watch the rpm..
Uh, if you are at a constant speed with a MT, your rpm will remain constant with or without A/C - unless your clutch is slipping.

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      07-17-2012, 03:29 PM   #20
toronto128
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huge difference between ac on/off on my 128 6 speed.
the rpms drop a lot between shifts.

like others have said, I just rev slightly higher between shifts, and smoother on the clutch

you should definately notice some kind of change with the compressor on
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      07-17-2012, 04:57 PM   #21
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Quote:
Originally Posted by Tom K. View Post
Uh, if you are at a constant speed with a MT, your rpm will remain constant with or without A/C - unless your clutch is slipping.

Tom
How does it remain constant when a machanical compressor clutch kicks in?
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      07-17-2012, 05:35 PM   #22
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Quote:
Originally Posted by avecta View Post
How does it remain constant when a machanical compressor clutch kicks in?
While the A/C compressor increases engine drag, there is no speed difference as long as the mechanical (notice the spelling) connection between drives wheels and engine is unchanged - which is the case in a MT unless a gearshift has been made or the clutch is slipping.

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