This paper describcs electronic control technologies for a variable capacity heat pump air conditioner. ln this paper, we discuss how the following control items should be realizd. The first is the improvement in heating seasonal performance factor. The question as to whatneeds to be done about the control of the electronic expansion valve so as to keep the superheated amount of the refrigerant at the compressor inlet at the optimum level not only during continuous operation but also during start-up, remains to be answerd. The second is the reduction of start-up time. The frequency is rapidly accelerated in order to reduce the start-up time. The way in which the frequency is to be accelerated must be below the upper current limit allowed by the inverter by establishing a correlation with the time constant of the refrigeration cycle response.