The condensing unit functions by compressing gas, or refrigerant, as it pumps through a system of coils. The refrigerant then becomes a high temperature, high pressure liquid, as it flows through copper tubing attached to a furnace.
The refrigerant expands and becomes a low temperature gas that absorbs heat as it passes through the home ductwork system. Moisture that condenses outside the coils is carried away by a drain.
Grass and Leaves
Grass and leaves built up around the AC condensing unit may cause it to stop running. Removing debris after mowing grass and cleaning the unit may return its functions.
The AC condensing unit may not be running because the circuit breaker is off. You may simply need to go to the breaker box and flip the switch on.
A blocked outdoor unit may inhibit air flow, causing the home to not get enough air or heat. A monthly filter change encourages proper air flow.
It the unit does not run after simple changes, you may need to call a professional repair person, who will be able to detect mechanical issues restricting air flow.