what tells the pcm to raise the idle when you turn on the air conditioner ?

 

Your Idle Air Controller is always adjusting to keep your idle at the target value.

 

so if my idle drops low when I turn on my air and it never goes up I'm guessing the IAC is bad ?

 

It could be that your throttle body, which houses the IAC, just needs to be cleaned. If the passage or IAC valve is dirty, it may be trying to let more air in, but can't flow enough. I'd clean your TB. Carefully clean the IAC valve, it's a delicate piece (mounts to the lower left front of your TB where the connector plugs in.