American Standard AC/Heating Unit won't come on?

Hoping someone out there can point me in the right direction on this problem, would rather fix myself if possible. This is a central heat/air unit outdoors, as of today the AC won't come on. I've shut off the t-stat and turned back on after a few minutes, cleaned dust out of the t-stat, turned the breaker off and back on, changed an air filter also. I've read about a reset button someplace on these outdoor units but I'm not certain where that would be. Any general advice or specific info on finding that reset button is appreciated.