Method for controlling operation of air conditioner

A method for controlling operation of an air conditioner is provided to restrain start of defrost operation due to frost in course of heating operation to prevent discomfort due to defrost operation. A controller judges whether an air conditioner is operating(S200). The controller judges whether an operation mode selected by a user is heating operation(S202). If so, the controller switches a four-way valve to start heating operation(S204). An outdoor heat exchanger temperature sensor detects a temperature of an outdoor heat exchanger changing during heating operation to prevent frost(S206). The controller compares the temperature of the outdoor heat exchanger with a preliminarily set reference temperature to judge whether the temperature of the outdoor heat exchanger is below the reference temperature(S208). If so, the controller lowers operation frequency of a frequency variable compressor or reduces the number of multi-type compressors to increase an evaporation temperature of the outdoor heat exchanger to prevent frost(S210). The controller counts operation time for preventing frost to judge whether operation time for preventing frost is more than reference operation time(S212-S214). If so, the controller raises operation frequency of the frequency variable compressor or increases the number of multi-type compressors to return to normal heating operation(S216). If an operation-off command is inputted, the controller judges whether operation of the air conditioner is off(S218).