Abstract: The operation of indoor devices in a multiple unit air conditioning system are monitored by an operation sensing portion. After all the indoor devices are turned off, the compressor continues to operate for a length of time determined by the time constant delay portion and then is turned off. Once the solenoid valves 4 feeding refrigerant to the indoor heat exchangers 3 are closed, the continued operation of compressor 6 causes an over-pressure relief valve 8 to open. This equalizes the pressure difference between the suction line and the high pressure discharge line of the compressor and thereby allows for faster restarts than a conventional bypass line 9.