Most central outdoor AC units are built to handle ordinary weather. A cover is optional for some models; if your manufacturer recommends one, use a breathable, correctly fitted cover only while the air conditioner is off for the season. Remove it before cooling starts again, and keep leaves and debris away from the unit.
Do not wrap or fully cover an outdoor heat pump that heats your home in winter: it needs open airflow to operate. If you are unsure which system you have or how to protect it, ask Stanley during air conditioning service.