Most central air conditioning systems run on AC. However, many of the more advanced and efficient air conditioning systems on the market today use inverter technology. An inverter system converts the AC current into DC. With an AC system, the compressor is either on or off, causing the unit to repeatedly start and stop to maintain the desired room temperature. Compressors which run on DC power are smaller, quieter, and can be modulated up or down to run at different speeds, like a dimmer switch on a light fixture.