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Discussion Starter · #1 ·
noticed a few times while i'm sitting at a stop light my AC will kick on and it feels like there is a car that just bumped me. i check my rear view and there isn't even a car anywhere close.

tonight on the highway i decided to do a little test. had the fan set to low with the temperature dial set to cold. i tried to manually hold the throttle as constant as possible at 55mph. felt the AC kick on and the truck would start to slow. it was almost as if i hit a strong head wind. i then give it a little more throttle and hold it at 55mph again. i hear the AC relay kick off and the truck starts to speed up.

then i tried turning the AC completely off. no strange throttling as when it was on.

anyone else experience this? is there a problem? maybe the belt is too tight?

maybe i am just over-thinking this.
 

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ya i sit at a red light, and i can hear a relay kick on or off not sure, and my truck will jump forward just a bit
 

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Uhhh.. what?
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Normal, as everyone has mentioned. Mine does it too.

When idling and the AC kicks on, the computer bumps up the idle speed to compensate (i.e. so the motor doesn't stall/lug), hence the bump/surge forward.

For highway speeds, as Johnny_5 said, takes HP to run the AC.
 

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What you are feeling is the clutch for the compressor engaging which is driven by the serpentine belt and the computer does raise idle to accomadate the load.
 
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