AC causes car to shut off

Be prepared to replace the IAC but you can try cleaning it first.

No but it's the first thing to check since it is what kicks up the idle for the load of the AC, and it is an item that gets worn and/or dirty periodically.

IAC doesn't work: look for +12 volts at the IAC red wire. Then check for continuity between the white/lt blue wire and pin 21 on the computer. The IAC connector contacts will sometimes corrode and make the IAC not work. The red wire on the IAC is always hot with the engine in run mode. The computer provides a ground for the current for the IAC. It switches the ground on and off, making a square wave with a varying duty cycle. A normal square wave would be on for 50% of the time and off for 50% of the time. When the idle speed is low, the duty cycle increases more than 50% to open the IAC more. When the engine speed is high, it decreases the duty cycle to less than 50% to close the IAC.



An old-fashioned dwell meter can be used to check the change: I haven’t tried it personally, but it should work. In theory, it should read ½ scale of whatever range you set it on with a 50% duty cycle. An oscilloscope is even better if you can find someone who has one and will help.



See the "Surging Idle Checklist for help with all your idle/stall problems. Everything you need to find and fix idle problems is in there.

The first two posts contain all the updates to the fixes. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.

Dwell meter, man I havent seen one of those in a while, long while.

Yes you can bet on it being an IAC. I've seen it caused by the signal not going to the computer telling it that the AC is on, but not that often, and I have seen it more than that where the compressor starts locking up but usually that is acompanied by some belt squeel.

Usually even if the computer isn't getting the AC signal it usually catches it before it stalls.