The cooling or heating required by an air-conditioning varies depending on various factors ie. outdoor temperature and the amount of heat in the room.
Fixed speed compressors deliver fixed amount of cooling power, so the compressor must start and stop to maintain the room temperature that is desired. In Inverters, the speed varies as per the load required, giving accurate cooling or heating.
In an inverter system as the compressor ramps up to high speed, the flow of refrigerant through the system increases the cooling capacity and as the compressor speed decreases the flow of refrigerant decreases through the system thus reducing the capacity. This is a major energy saving and cost effective factor.