PURPOSE: To prevent an irregular increasing of high pressure in the event that an indoor air temperature is increased by a method wherein an air conditioner is provided with a control device to open a solenoid valve for a specified period of time when the indoor air temperature is increased more than a predetermined value during a heating operation.

CONSTITUTION: A refrigerant heating type air conditioner has a refrigerant circuit which is constructed to have a cooling cycle A and a heating cycle B within one closed circuit. A control device 18 includes a valve opening time discriminating means 21 for discriminating a valve opening time of a solenoid opening or closing valve 12 in response to temperature information got from an indoor air temperature sensing means 9 and an outlet refrigerant temperature sensing means 20, and a valve opening or closing control means 22 acting to open the solenoid valve 12 for a predetermined period of time in response to a signal from the discriminating means 21. In the even that the indoor air temperature is sufficiently high, a heating cycle B and a cooling cycle A during stopping of operation are communicated from each other, a predetermined amount of refrigerant is sent from the heating cycle B to the cooling cycle A and then a circulating amount of refrigerant at the heating cycle B is properly kept.