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this seems to happen in both my 96 900 and my 93 9000, when the aircon cycles on I think I feel a hesitation from the engine. How could that be?
 

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When the AC "cycles", the electric clutch at the compressor pulley engages, this couples the pulley and the A/C compressor, the compressor starts to turn.

The compressor is an additional load on the engine. On some cars, people notice a hesitation while driving, I am not sure why though. Just better observers, maybe.

At idle, the ECU is supposed to open the IAC valve a little to raise the rpm a second or two before the compressor turns on, so you actually see a small movement up in rpm if you happen to be watching he needle at the time.
 

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Mm

I didn't think the AC load would be enough to do that. I was figuring I had a fault in both cars.
 

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rawill said:
I didn't think the AC load would be enough to do that. I was figuring I had a fault in both cars.
Sometime when you are stopped for a while with the AC on, look at the rpm, and wait for the AC to cycle. There should be a small "bump", just before it happens. That will pretty much tell you if all is working as it should. (easier to observe at idle with little other load on the engine)
 
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