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07-17-2012, 05:57 PM | #23 | |
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You know there's a clutch on the a/c compressor right? There's a rotor friction plate and a a/c compressor friction plate, and when the a/c is off only the rotor plate is spinning freely to the compressor plate (a/c compressor).. When it's turned on, there is electro magnetic field through the rotor which pulls together the rotor and compression plate thus MORE drag on the engine than just a rotor pulley it is now spinning the compressor..... |
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07-17-2012, 06:02 PM | #24 |
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One thing to note is the OP probably drives a manual car. A manual car is a lot more sluggish with the ac on. You have to rev the gears higher before shifting to avoid jerking the car, rev match when shifting to avoid jerking the car, etc... You have to drive the car way different when the ac is on. With an auto it doesn't matter hit the gas and it goes the same ac on or off.
My car is manual and every manual car I've owned with the a/c on you have to drive the car a little different to not make jerky shifts. Just the way it is. |
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07-17-2012, 06:49 PM | #25 | |
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07-17-2012, 07:06 PM | #27 |
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Ah, so this 1-2 and 2-3 clutch disengagement jerk on the 6MT is normal with the A/C on? I couldn't even figure out how to turn the A/C off this afternoon when I was driving around with the windows open.
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07-17-2012, 07:25 PM | #28 | |
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Over all, no I don't notice the type of power loss that you describe. Remember, a turbo engine puts out low/modes torque when there is no boost. It's the nature of a turbo engine. If you use very light throttle where you're not building much boost, then power is modest, so if you're using very light throttle and AC is on, then you'll notice the drag more so. If you drive it normally, or at least normal for enthusiast driving , then you're using more throttle and thus more boost. That boost creates more power and it easily has plenty of power to overcome the AC drag. Even with AC on I can still smoke the rear tires off the line, if I want to. I've done it with AC on an off. I don't do that often though as it's wasteful. Maybe you've got a boost leak somewhere, or something else is wrong? |
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07-17-2012, 07:36 PM | #29 | |
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Driving my Civic with the A/C on in the summer really annoyed me because of the performance hit, its a bit disappointing to feel the same even with an inline six under the hood. I thought the 135i would fare better in terms of how noticeable the performance drop is but it doesn't sound like that is the case from this thread. Its too bad because summer is the best time to drive the car (drier roads, no snow, summer tires are on) but if it gets too hot and the A/C goes on it kind of robs the experience. |
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07-17-2012, 07:41 PM | #30 | |
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You said to drive at a "constant" speed, then turn the AC on and see what happens to RPM. Well, vehicle speed is a function of engine rpm and gear ratio. Thus, if you're driving at a 'constant', say, 55mph, then even if AC kicks on it has no bearing on gear ratio and engine rpm. I think what you wanted to say, is that when the AC kicks in the compressor drag on the engine will bring engine rpm down, and it will. But then, you're not going to moving at that "constant" speed, your speed will decrease if you don't compensate by giving more throttle in bring engine rpm and speed back to where it was. Your comment should have included the whole point you were trying to make. You are correct that AC compressor drag will result in putting a greater load on the engine, and if the driver doesn't compensate, then engine rpm will come down, and speed will decrease. But, the question at hand is how great is that drag? Most don't notice a big drag, especially with the 135i and it's more powerful engine. You can see and feel this drag when at idle. When idling note the rpm, now turn the AC on. You will feel the compressor kick in and the engine slow down, but quickly the idle speed control kicks in and raises idle rpm to compensate. In some cars, the throttle increases but engine rpm is brought to the same rpm as before the AC kicked in. In other cars, like our 135i, the engine rpm actually goes higher by about 100-150rpm, at least in an MT 1. I understand the point you were trying to make. Jim was clarifying your comments overly simple wording. My intent is not a dig on you, I'm just saying that the way you worded your comment left out much that would have helped clarify your message. I'm a verbose person in conversation and in writing. Often I write too much. The converse of that is people who write too little and their message doesn't get across as it should. |
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07-17-2012, 07:47 PM | #31 | |
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07-17-2012, 07:49 PM | #32 | |
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In either car you have to adjust your throttle input. In an MT you simply use more throttle to compensate for the added drag. In an AT, as well, you have to use more throttle to compensate or the added drag. As for the "jerkiness", that's up to the MT driver. If the driver has a lazy shift, then he may get a more jerky feeling as the rpms will drop a bit quicker compared to no AC drag. In an AT there is of course no tendency for a "jerky" shift as the shift is done differently. More throttle. That's what is needed. OH, and no lazy shifting, which one shouldn't be practicing in the first place. |
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07-17-2012, 07:51 PM | #33 |
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07-17-2012, 07:51 PM | #34 |
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6MT here and was also surprised by the impact of A/C. Don't notice it on my family cars, but they have all been automatic (and not driven as spiritedly).
I have an old habit (started a while back and continued with my past few cars) of turning off A/C when merging onto one particular highway (almost always go WOT). Turn it back on once I've merged and at cruising speed. Even in the 135i, I still do this. |
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07-17-2012, 07:57 PM | #35 | |
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07-17-2012, 07:58 PM | #36 | |
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Common? Yes, if your MT skills need work. You need to practice your MT shifts. No lazy shifting. Learn to shift quickly all the time. That way, when the AC brings the engine rpm down quicker, you can shift quickly and smoothly. Since you know the rpm will drop quicker, then pick a higher rpm to shift. If you use 2000rpm for a smooth shift, then use 2300 or 2500 when the AC is on, or shift quicker. |
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07-17-2012, 07:59 PM | #37 | |
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Do you drive around with A/C on at all times? |
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07-17-2012, 08:07 PM | #38 | |
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Not sure about a boost leak but maybe that's something I'll ask the dealer about. Sometimes even with A/C off I don't feel I'm getting the response and power that I should. And like I said in one of my previous replies, I don't know if I have DME programming issues possibly reducing power and throttle response to some extent or not.
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07-17-2012, 08:10 PM | #39 |
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I've always done this as well, especially in my '01 Prelude SH. I was hoping I wouldn't need to with the 135i. Don't actually need to, but it feels better if I do.
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07-17-2012, 08:48 PM | #40 |
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Actually it's good to drive with the AC on all the time, even in the winter the automatic mode turns the AC on. This way all the gaskets and o-rings in the AC lines are kept well lubricated. Never using the AC is a big part of failing AC systems.
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07-17-2012, 09:23 PM | #41 |
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Thanks, that is a good point. My Honda Civic's manual recommended turning on the A/C a few times during the winter to keep it in good working condition but leaving it on all the time? Sounds like it might be good for the A/C but wasteful of gasoline and just robs the driving experience (car drives better with it off). I'll turn it on occasionally but won't drive with it on all the time in the winter.
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07-17-2012, 09:30 PM | #42 | |
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07-17-2012, 09:30 PM | #43 |
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I drive with A/C on all the time. Unless its time to show someone what I've got.
Then I come home, sweaty, and the wife goes "Who did you beat this time?" "Well, there was this guy..." |
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