Hello, and thank you for letting us help you with your automotive question. Typically this is caused by a dirty throttle body. When the throttle body is dirty it cannot easily change the idle of the engine to compensate for added loads like the a/c system. You would simply need to remove the air intake hose from the engine and use throttle body cleaner and a lint free cloth to wipe it out. Do you plan on fixing this yourself?
This can be an unrelated issue. Low flow in the exhaust or in the EGR system typically means the system is dirty. It can also mean a bad converter. Neither of these will cause the problem you are having without other symptoms also. You would have no power and a rough idle all of the time.