Quote:
Originally Posted by avecta
I'm sorry mr english teacher  . Typing on the phone whilst driving* 
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..... |
Jim was responding to your overly simplified comment.
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.