A method of controlling a heat source-heat exchanger fan that blows air to a heat source-side heat exchanger that performs heat exchange with refrigerant compressed in a compressor, the method comprising: a first converting step of converting from a current detected temperature at a current time of a temperature detector attached to the heat source-side heat exchanger to obtain a current converted high pressure value at the current time of the refrigerant inside a high pressure-side pipe of the compressor; a second converting step of converting from a past detected temperature that the temperature detector detected at a past time before the current time to obtain a past converted high pressure value at the past time of the refrigerant inside the high pressure-side pipe; and a fan speed determining step of finding a corrected converted high pressure value by correcting the current converted high pressure value with the past converted high pressure value and using the corrected converted high pressure value to determine the speed of the heat source-side heat exchanger fan; wherein in the fan speed determining step, the corrected converted high pressure value is obtained by finding a rate of change of the current converted high pressure value in the neighborhood of the current time from the current converted high pressure value and the past converted high pressure value and adding the product of the rate of change and a correction coefficient to the current converted high pressure value; wherein an outdoor temperature discriminating step of detecting the outdoor temperature of outdoor air that is the air-blowing target of the heat source-side heat exchanger fan and discriminating whether the outdoor temperature is in a first temperature region or a second temperature region higher than the first temperature region, wherein in the fan speed determining step, when it has been discriminated in the outdoor temperature discriminating step that the outdoor temperature is in the first temperature region, the corrected converted high pressure value is used to determine the speed of the heat source-side heat exchanger fan, and when it has been discriminated in the outdoor temperature discriminating step that the outdoor temperature is in the second temperature region, the current converted high pressure value is used instead of the corrected converted high pressure value, or another corrected converted high pressure value found using another correction coefficient which is different from the correction coefficient used in the first temperature region, to determine the speed of the heat source-side heat exchanger fan. a first converting step of converting from a current detected temperature at a current time of a temperature detector attached to the heat source-side heat exchanger to obtain a current converted high pressure value at the current time of the refrigerant inside a high pressure-side pipe of the compressor; a second converting step of converting from a past detected temperature that the temperature detector detected at a past time before the current time to obtain a past converted high pressure value at the past time of the refrigerant inside the high pressure-side pipe; and a fan speed determining step of finding a corrected converted high pressure value by correcting the current converted high pressure value with the past converted high pressure value and using the corrected converted high pressure value to determine the speed of the heat source-side heat exchanger fan; wherein