Low idle with a/c on

So, when I have my a/c on, and when I pull up to a stop and am idling, my engine idles around 600-700 RPM. Isn't there supposed to be something that kicks the idle speed up when the a/c is on? What is it that controls that? Is there just an adjustment somewhere? It rattles like mad when the idle is this low. (that could be a bad motor mount but that's another issue all together)

Yes there is the ECU is suppose to do that with the IAC motor. If the system is over charged it could also cause low idle because some liquid is getting back to the compressor. Listen for a slight knocking noise coming from the compressor.

Ya, it knocks when the idle drops. But it goes away if you touch the throttle and bump up the RPMs a little.

langer1 said:

Yes there is the ECU is suppose to do that with the IAC motor. If the system is over charged it could also cause low idle because some liquid is getting back to the compressor. Listen for a slight knocking noise coming from the compressor.

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So, if there is a knocking noise do I need to have the A/C checked? Do you think that the compressor can be damaged?