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Old 08-02-2016, 07:39 PM
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poor acceleration with A/C turned on

My '97 SL320 runs great until I turn on the A/C. When I have the A/C on, the car will sometimes not respond to acceleration. In fact, I'm afraid to pull our into traffic because I'm not sure if the vehicle will even move. When I accelerate from a dead stop, sometimes it acts normal and other times it just sits there even when I push the accelerator all the way down. It eventually will seem to catch and move, but I never know when it will and when it won't. If I turn off the A/C, the car again responds normally. Does anyone else have this problem or know how to fix it?

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Old 08-03-2016, 04:39 AM
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Sounds like a possible idle up problem. Usually the ac seems to bog down the car normally so when it's engaged the idle raises slightly to compensate. I would see what others have to say, but I believe this is correct.

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Old 08-03-2016, 08:46 AM
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(Although =>

More specifically there's a signal sent to the ECU to adjust the idle when the AC is switched on so the engine can compensate. Check the wiring first.)
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Old 08-03-2016, 09:26 AM
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My car the ac will cut off when gas pedal is pressed to the floor.It is supposed to do that.
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Old 08-03-2016, 12:23 PM
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This sounds more serious than just feeling the added load on the engine due to the compressor being engaged; perhaps something with the throttle system's electrical supply, etc. Are the battery and alternator good? Are the electrical grounds all good?
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Old 08-03-2016, 08:38 PM
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What is the history of this car? How long have you owned it? Did this happen after a recent repair?

The AC does not pull enough mechanical engine power to drag the motor down as you describe so you are going to have other issues.

This car uses drive by wire, there isn't a mechanical cable that runs to the throttle body, the gas pedal sends signals to the engine computer. Mercedes tends to place a bunch of ground wires under one bolt. If the bottom and top ones corrode, the middle ones start to communicate with each other and all sorts of odd behavior can occur.

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