Methodical engine Lagging with AC on

Old 05-19-2014, 11:20 PM
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Default Methodical engine Lagging with AC on

I everyone,

This has to be one of my favorite places to read about 968s on the internet. What a great group of folks. I think Jeff also has my car information in his database.

I'm wondering if anyone has an idea about what might be causing a methodical lagging in the engine with the AC turned on. I'm a bit worried about it, to be honest. There is no engine lag at all with the AC turned off. Also, the AC is usually set to the second line on the left side of the control know so it is blowing fairly cold,

Thanks for any suggestions.

Oh! One more thing... Does anybody have suggestions for fixing the cruise control?

Thanks again.
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Old 05-21-2014, 10:44 AM
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Location: Tampa FL
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It's possible that the expansion valve is stuck closed or that there is some other restriction causing too much high side pressure which will cause the compressor to create more drag on the engine. I would fit a set of gauges first off to verify that high and low side pressures are as they should be.
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Old 05-21-2014, 12:30 PM
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When the ac system is properly charged, pressures are OK, there is not 'lag' or delay on acceleration. An overcharged system will draw more hp, or a system with unusual high side pressures will do the same thing. A normally operating expansion valve that is "closed" never fully closes otherwise you would see a low side pressure down to "0". Bikepilot suggested tossing on a set of gauges, good idea. Your ac tech can check the low and high side pressures at idle, using a P&T chart, and raise the idle to check if things are not normal.

"If" there was a vacuum line actuating an actuator, say for an air flap or other device, and there was a leak in that air circuit, that might cause a lean condition and your would experience a lag.
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Old 05-22-2014, 05:41 PM
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Idle speed motor makes up for the extra draw on the engine. Check the small wires on the top of the AC compressor and make sure it is plugged in. It sends a signal to the DME that the AC is on so when decelerating, the idle speed motor kicks in prior to the rpm dropping below 1100 or so to alleviate the dip on decal from the AC drag. Do your radiator fans run when the a/c is on?
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