PURPOSE: To enable a heat treatment air conditioning operation and an indoor air processing to be facilitated and efficiently carried out and to provide an entire small-sized shape by a method wherein a heat exchanging chamber and an upper and lower blower chamber divided into two sections are formed in a U-shaped air blowing passage and then an air supplying or discharging adjustment chamber having a discharging damper, a surrounding air intake damper and an air feeding damper is disposed at an intermediate part of the upper and lower blower chambers.

CONSTITUTION: An air blowing port 2 and an air returning port 3 disposed at an upper part of an air conditioner 1 are communicated with a U-shaped air blowing passage A and at the same time a heat exchanging chamber B, an upper and a lower blower chamber C and D are formed at a right side and a left side of the air passage. Each of a discharging damper (a) and a surrounding air intake damper (b) is opened, an air feeding damper (c) is closed, the upper and lower blowers C and D are operated, and then cooling or heating air heat exchanged with fresh surrounding air is fed into each of the chambers through a duct communicated with the air blowing port 2. Concurrently, contaminated air in the room is passed from a return port 3 into the blower chamber C through the duct and is discharged out of the air conditioner through the air discharging port 16. The air feeding damper (c) is opened in response to a temperature environment in the room, thereby only a part of the indoor air is released out of the air conditioner to heat the cooled or heated air in the room again and at the same time the surrounding air is fed into the room and then the air is fed into the room as the mixed air.