[preDoc 328]

Originally Posted by konradsa

Really weird everybody has such issues. Compared to the cars I previously owned, I barely notice any difference in my car (328i auto) with A/C on or off, even on a hot 100F day. I was already wondering whether BMW has done something to make the A/C less noticeable, e.g., make the gas paddle more response with A/C on.

It seems that this effect is much more pronounced with MT.

Yea I've never noticed an A/C issue with an auto car before. I've only driven stick for 2 yrs so I can't really say too much, but my E34 5spd that I learned stick on never had the inconsistent shifting issue. However, it was extremely hard to shift on cold winter startups (maybe I was still learning back then?). The shifting in that car was also much slower than the E90. I had to relearn my shifting when I got this car. Now I'm used to it, I think newer MT's require quicker shifting in general.

[Tom K.]

While I've never had a problem with MT BMWs using A/C, I noticed today in 102o temps that the revs do drop rather quickly with the clutch in which may be causing the difficulty for some folks. Since I always shift briskly, it's simply a matter of timing the clutch release to coincide with the rpm drop - in other words, don't dawdle with the clutch in. It works for me at all revs - from below 2,000 (as an experiment) to 4,000.

While I haven't noticed much of a power drop with A/C, the gas mileage on both my 128i & 328i suffers by about 5~10% - a cheap price given our current weather.

Tom

[cimbali]

Originally Posted by nineth

This is obviously not the right way to work around the issue. You have three options: (1) drive with a/c off when not on the highway, or (2) shift at about >= 3.7k rpm

on my morning drive today I tried option (2) above instead of rev-matching the upshifts and definitely liked this option the best... I found it easier to catch the revs and overall had a much smoother ride. Although, I did have some difficulty with the 4 to 5 shift which is probably due to that shift being my slowest.

[zaheer]

no change in performance for me...yes i have 6mt too...my 335 is pretty slow anyway

[vasillalov]

6MT here. No such "issues" when the AC is turned on, regardless of its setting. Yes, the car is slightly more sluggish but none of that rapid rpm drop anyone is talking about.

Also, our cars are designed to shut off the AC compressor if you romp on the gas pedal. If you drive smoothly then AC compressor is always on when AC is switch is on. If you go for several WOT pulls, the AC compressor will switch of at like 50% throttle body angle till you back off the gas pedal.

[Driv3r]

this happens to me as well...

[nineth]

Originally Posted by Tom K.

While I've never had a problem with MT BMWs using A/C, I noticed today in 102o temps that the revs do drop rather quickly with the clutch in which may be causing the difficulty for some folks. Since I always shift briskly, it's simply a matter of timing the clutch release to coincide with the rpm drop - in other words, don't dawdle with the clutch in. It works for me at all revs - from below 2,000 (as an experiment) to 4,000.
Tom

But try driving like this (w/ the a/c on for a few days), and you'll completely mess up your memory causing you to shift too fast for a/c off conditions; also, the compressor may itself turn off once it's cooler inside or outside.

[nineth]

Originally Posted by vasillalov

6MT here. No such "issues" when the AC is turned on, regardless of its setting. Yes, the car is slightly more sluggish but none of that rapid rpm drop anyone is talking about.
.

This is interesting; can you confirm with a/c on and fan speed at max (set manually) at about 3000rpm? If the auto light is on, a/c compressor may be off regardless of fan speed (obviously depending on outside temperature). May be this issue does not affect 335.

[SteveC]

Originally Posted by Wissam

I normally shift around 2700-3000 rpm, but I noticed when the AC is on it becomes hard to shift smoothly at these rpms and I would have to go north of3500 rpm to help smooth the shifts out. Are you guys noticing the same thing? I know the AC puts extra load on the engine, but it should not be this noticeable on an engine this size.

Several reasons:

The AC compressor is designed to switch off during moderate to hard acceleration. Shifting at 2.700 obviously your foot is only 'tickling' the gas, so quite possibly the compressor remains engaged

The AC takes a constant load off the engine, wheras engine power output varies with RPM, so at low revs, the AC load is quite a high percentage of total power and therefore exerts quite a drag on the engine relative to the engine's relatively low output

Gearboxes are always baulky at very low rpm....the lower the rpm, the slower the shift tends to be and 2,700-3,000 rpm must be just above that 'limit'. With the AC turned on, revs drop quickly due to the relatively high engine load and the shifts become 'baulky' .

Why baulky at low rpm? Its a matter of the relative differential between engine and transmission rpm. Gear ratios are fixed, so a 500 rpm difference at 3000 rpm represents a 17% differential whereas at 7000 rpm its 7%. The bigger the differential, the more difficult it is to shift gears smoothly

[Oddball]

(My first post)

When I went for a test drive in June before buying my car, I noticed the same thing. Biggest shifting issue was between first and second. But after a few days after purchasing, I was able to shift smoothly between all gears.

For me, driving my 330 was like learning how to drive stick all over again. My IROC essentially has four acceleration and one cruising gears. In the 330 there are six acceleration gears. In the IROC I was used to taking my right foot off the gas when shifting; in the 330 I just have to keep the foot on the pedal slightly.

It's been too damn hot here to drive without the AC so I'll see if there is a difference without the HVAC on.

[i2iSTUDIOS]

it's not too big of a deal, ac on or off, it's still a great car.

[seis-speed]

Originally Posted by epiphone3

I notice the same thing... I try to keep the AC off as much as possible.

I agree, it really is the same in every car I have every had. Used to drive the Vegas to Phoenix road with various sports cars and it always amazed me how much the AC affects the engine.

[srcstc]

Originally Posted by Matt@Camber-Toe

i have noticed that as well...below 3000 rpm the engine drops like a rock and I have to quick shift or blip the gas to keep it from lurching.

Same here. You have to shift faster to keep up with the faster dropping RPMs. Hate driving w/ the AC on.

[nineth]

Originally Posted by seis-speed

I agree, it really is the same in every car I have every had. Used to drive the Vegas to Phoenix road with various sports cars and it always amazed me how much the AC affects the engine.

No, it is NOT. I drove a Mazda Speed 3 2010, and the A/C does not create a difference so significant enough to change your shifting technique; I have also driven much low power cars in other countries (< 1.1l, 4 cyl) and haven't noticed this problem. So, may be you don't have the problem most people are talking about here.

The problem actually being reported by everyone here is the "amount" of effect the A/C has on the rpm drop after the clutch is disengaged, and it is so much that many prefer to shift without a/c most of the time. The fact that a/c puts load on the engine is well-known and true for any car, but the amount of effect this load has at "no throttle and with the engine disconnected" is ridiculously high for at least my E-90 325xi.

[srcstc]

Originally Posted by nineth

No, it is NOT. I drove a Mazda Speed 3 2010, and the A/C does not create a difference so significant enough to change your shifting technique; I have also driven much low power cars in other countries (< 1.1l, 4 cyl) and haven't noticed this problem. So, may be you don't have the problem most people are talking about here.

The problem actually being reported by everyone here is the "amount" of effect the A/C has on the rpm drop after the clutch is disengaged, and it is so much that you prefer to shift without a/c most of the time... The fact that a/c puts load on the engine is well-known and true for any car, but the amount of effect this load has at "no throttle and with the engine disconnected" is ridiculously high for at least my E-90 325xi.

My GF's VW Beetle doesn't do this and it's also a manual. My old E46 didn't do it either. Both my old E46 and my GF's Bug ran/run a little sluggish with the AC on but they don't do this.

[Tom K.]

Originally Posted by nineth

But try driving like this (w/ the a/c on for a few days), and you'll completely mess up your memory causing you to shift too fast for a/c off conditions; also, the compressor may itself turn off once it's cooler inside or outside.

No difference for me - A/C on or off, never a problem shifting a BMW (and I'm on my 5th). As long as you shift quickly, which is the way I've driven ever since my Renault R5 forced me to do otherwise some 30 years ago.

Tom

[nineth]

Originally Posted by Tom K.

No difference for me - A/C on or off, never a problem shifting a BMW (and I'm on my 5th). As long as you shift quickly, which is the way I've driven ever since my Renault R5 forced me to do otherwise some 30 years ago.
Tom

Do you always shift at medium to high RPMs (>= 3.5k)? At those RPMs, a/c on/off does not make a difference.

[Thud]

I have a 6MT and never noticed this "problem." Yeah there's a slight difference in how it shifts... I guess I just have adapted my shifting and I don't notice. No big deal.
I've actually had the problem worse in other MT vehicles I've owned.

My only complaint is that the A/C sucks in the first place.

[badassfajita]

I think this "problem" exists only if you shift lazily...shifting quickly w or w/out the ac is solid.

[nineth]

Originally Posted by badassfajita

I think this "problem" exists only if you shift lazily...shifting quickly w or w/out the ac is solid.

This is what I thought at some point, but found it to not be the case. I can
shift fast enough to shift smoothly w/ AC on, but if I shift this way when the
A/C is off, it's a mess. I can't just let the clutch out so quickly when the a/c
is off without getting a lurch forward (esp. for 1-2, 2-3 shift).