| 摘要 |
PURPOSE:To accurately determine the number of indoor units which are switched on and prevent a transmission failure between the indoor units and outdoor unit by incorporating plural shorting means between signal generating means and signal receiving means, and identifying the switching ON or OFF of the indoor units based on the signal level under a condition where a certain shorting means is selectively activated. CONSTITUTION:If an indoor unit is switched ON, the difference between the cathode side signal level of a light emitting diode 6 and the collector terminal side signal level of a switching transistor 4 becomes equal to the sum of a voltage drop due to other shorting switches and a voltage drop due to resistor 10, light emitting diode 8 and phototransistor 9 of the indoor unit. Therefore, by determining the magnitude of the voltage drop by a level comparator circuit 11, a determination can be made as to whether the indoor unit is being switched ON. After the initialization, only a shorting switch 55 is opened by a selection means, and when the indoor unit 21 is selected and the switching transistor 4 is turned ON-OFF based on the control signal from a control section, the ON-OFF signal is transmitted to the indoor unit 21 through a signal transmission path 3.
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