<p>A refrigerant circuit is formed by connecting an outdoor unit (5) and an indoor unit (6) to each other with communication piping (18) including a gas pipe (16) and a liquid pipe (17). An alternative refrigerant R-410A is used as a refrigerant to be circulated through the refrigerant circuit. For middle-sized and large-sized air conditioners whose rated cooling power (JIS C 9612) is not less than 4.0 kW, a gas pipe (16) having an outer diameter of about 9.5 mm (with wall thickness 0.8 mm) is used. For small-sized air conditioners whose rated cooling power (JIS C 9612) is less than 4.0 kW, a gas pipe (16) having an outer diameter of about 7.9 mm (with wall thickness 0.8 mm) is used. <IMAGE></p>
