The disclosure provides an air conditioner capable of smoothly performing communication between an outdoor unit and indoor units using piping communication, and a piping communication method thereof. When communicating between an outdoor unit and indoor units using piping communication, a communication mode is automatically changed to a differential mode and a single mode to set the most suitable communication method for field characteristics according to a communication state, so that communication between the outdoor unit and the indoor units can be performed smoothly. This enables smooth piping communication by increasing a communication success rate even if a physical short between refrigerant pipes occurs in a multi-system air conditioner that connects a plurality of indoor units to a single outdoor unit, or even if there are more branch pipes for branching the refrigerant pipe.