What is the chirping noise coming from when you turn your ac on then goes away when you rev your engine then comes back only when ac is on?

I believe that your alternator may need to be bench tested - when your a/c comperssor turns on (when your a/c turns on) this is a larger draw of required volts for your car, and therefore a larger load on your alternator. I believe that an alternator "struggling" to keep up with "demand" can cause the alternator belt to squeak. It could also be something as simple as a belt slippage - there is extra tension on the belt when another accessory is being used (your a/c). Check the condition of your belt. Think of paint finishes for a moment. If your belt has any "shiny" or "glossy" (called glazed) appearance, or has any cracks in it, then simply erplacing your belt could solve this. But if your belt is in good shape (has a dull or "matte" appearance), then have your alternator bench tested at a reputable auto parts store/mechanic. Another test you could do on your own is to start your car, then while it is running, disconnect the positive lead from your battery. If your alternator is running well, it should easily run your car on it's own w/out the battery. If your car stops running after disconnecting your battery, then your alternator is absolutely the culprit, and needs to be replaced. I am not a mechanic, but these are a few simple checks you can try yourself - good luck!

Belt or A/C clutch

Two other possibilities:

1. Most likely -- The belt is wearing out, getting loose, etc. Check the belt for glazing (makes it look shiny). Check also the strength of the belt tensioner.. (Take the key out of the car for this check!!) If you can pull the belt more than an inch toward you, the belt and / or tensioner may be bad.

2. The A/C compressor clutch is wearing out. This is not as likely. This would have to be repaired by a professional.