I have a 99 corolla when I'm in parking lots going 5-15 mph with my ac is on my car seems like its going to turn off. It makes this false start sound. When the a/c is off it doesn't do it. What is causing this?

It sounds like the Idle Air Control (IAC) valve is either sticking or dirty, or the Engine Control Module (ECM) isn't able to kick up the idle with the A/C on.
Try short bursts of throttle plate cleaner into the throttle body while the engine is running at operating tempurature. Don't let the engine stall. This may free the IAC if it isn't too badly gunked up.

Bad ignition wires can do this. I just fixed a problem on a '95 prizm with the same symptoms by replacing the wires with a new set of NGKs. The "old" wires were only about 18 months old and looked perfect, but had all the classic symptoms of performance issues. Realistically, they probably weren't bad so much as some cheap brand the last mechanic used.