To provide a structure for preventing freezing and thermal stress fracture capable of preventing the generation of an uneven back pressure at outlets of main tubes and preventing the freezing of drainage water to a degree the same as that in a conventional double-tube coil, in the single-tube steam coil of an air conditioner.

In the single-tube steam coil in which a plurality of steam move, in a heat exchanger of the air conditioner, orifices are formed at the outlets of a plurality of the main tubes constituting the single-tube steam coil, a steam inlet tube is communicated with an inlet header, an opening of the steam inlet is formed near a central portion in the longitudinal direction of the inlet header, and the direction of the opening of the steam inlet tube is determined at right angles with respect to the longitudinal direction of the main tubes.

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