PURPOSE: To automate the changeover of air cooling and heating by a method wherein electromagnetic switch coils are each connected in series with two contacts of a thermostat and connected in parallel with a power supply, and the normally-opened and normally-closed contacts of an electromagnetic switch are each connected to the power supply through a compressor and a four-way valve.

CONSTITUTION: The coils 15a, 14a of the electromagnetic switch 15 are each connected in series with the first contact 11a of the thermostat 11, which is opened when room temperature drops to t2, and the second contact 11 b, which is opened when room temperature rises up to t3 lower than t2, and connected in parallel with the power supply (not shown). The normally-opened contacts 14b, 15b of the switch 15 are connected in parallel and connected to the power supply through the compressor 18 and the four-way valve 16 is connected in reries with the normally-closed contact 15c and connected to the power supply respectively. When the load of air cooling decreases and room temperature drops to t4 due to the change of season, etc., the contact 11b is closed, an auxiliary heater 8 is conducted when a heater switch 12 is closed, the compressor 18 starts its operation, the four-way valve 16 is worked, and heating operation is conducted.