Panasonic Refrigerator Freezer NR-B30FX1 Inverter compressor

Model NR-B30FX1 is same as a NR-B30FW1 with a Inverter Compressor an Inverter PCB that supplies power to the Main control PCB and Front Display Board. There is no cooling Fridge or Freezer, lights are on, display on but compressor does not run. The internal cooling fan in Freezer (FC) not running in normal mode but does run briefly on power up with refrigerator compartment (PC) fan, and when un the diagnostic check 'Compulsion FC start function- s/c Test Terminal 1 & 3 on Main PCB.
Checked all voltages on boards, and swapped out Main Control Board with no difference, not swapped out the Invertor Board yet but checked thermisters/sensors and okay but can't find the sensor -ATC, for ambient room temperature to check it ?

Thinking it's the compressor ? So checked the three windings and all good 7.8Ohms and meggered to Eth all okay. Managed to get spare correct spec Panasonic compressor but not fitted, just connected the U,V & W three pin lead on to it and eth but no pipes connected. When power up refrigerator the Compressor does actually run for 2 seconds then stops, would of thought it would of ran for some time. Is this normal that it will stop after a few seconds and shut down when its not connected to the pipes. Does this prove the old compressor is faulty or it's something else ? Any advice please ?