Originally Posted by stealth13
Ya that sounds like mine, the rpm just drops from 800 , I can have lights and stereo cranked with 2 subs no problems, but the a/c... I dunno
The reason your RPMs drop with the AC on isn't because of the stereo, headlights, or disco ball in your car, it's because of the increased load on the engine.
As previously mentioned, check your ISC. When you turn your AC on, the ISC compensated for the increased load by opening up a little thus allowing more air in, and the RPMs should rise a little. (unless you've done some idle air nonsense to change that...) If they're dropping, I'm willing to bet your BISS is out of wack, or your ISC is toast.
To test the ISC, you want to disconnect the plug, get a DMM (digital multi-meter) and measure the resistance between pins 1-2, 2-3, 4-5, 5-6.
Someone might need to correct me here, but I believe you should get a reading between 28 - 32ohms. Higher is ok, lower.... well, I guess we'll see.
If you don't get any reading, or there is no connectivity between one of those 4 connections, your ISC is toast.