includes a decoder board 252 that includes a transient filter 254 receiving composite signal 212 from indoor unit 200 decoder board 252 also includes a processing unit microcontroller 256 that receives signals through transient filter 254 and controls operation of relay coil driver 258 relay coil driver 258 in conjunction with a dc bias power supply 260 and a 24 vac supply 262 control operation of compressor run relay 264 thereby controlling operation of a compressor not shown in one embodiment the components of decoder board 252 evaluate the signal on y u2032 for the presence of a combined compressor run signal and identifying signal from the ecm motor 204 shown in fig5 in this embodiment decoder board 252 through filter 254 and processor 256 are able to discriminate between a positive voltage containing both the blower identifying signal and a half wave dc signal the compressor run signal or no signal if the compressor run signal is present with or without the blower identifying signal compressor relay 264 will be energized if a preset time elapses without processor 256 detecting the identifying signal compressor relay 264 will be deenergized and locked out for a predetermined time otherwise the compressor and condenser fan will be allowed to run.