Common approaches to starting repairing a central air conditioning unit are to check the circuit breaker, thermostat and the internal switch. Dirty air filters also impact the circulation and the velocity at which the system blows out air.
The five main elements that make up an central air conditioning unit are the refrigerant, the compressor, the condenser, the expansion valve and the evaporator coil. Any malfunction in one of these components can cause the whole unit to fail. If a unit is not working, check that the thermostat is set in the "cool" position as opposed to the "off" or "heat" setting. The thermostat for the air conditioner must also be set below the current room temperature. Any damage to the 240 volt circuit breaker controlling the air conditioning compressor or the 120 volt circuit breaker controlling the furnace will also lead to failure of the system, so check these components for damage.
Inspect all duct work and check for any disconnections. The attic, basement and crawl spaces all need to be inspected. In some instances, a central air conditioning system may be too large for a particular household. In this scenario, the only feasible solution is to replace the condensing unit and associated coils with a system that is more suitable.