Thermal cutout (compressor overheat) could be caused by high superheat. High pressurelockout means the head pressure was too high more than once and the board locked it out from trying to start again. If your illustrious "teacher" is not going into these details but is rather changing random parts, you are in need of better tutelage.
Learn to take superheat, subcool, temp diff, amp draw, cap readings, static pressure readings and you will go far in your troubleshooting ability. Until you understand what these readings mean, it will be difficult to troubleshoot HVAC.
High superheat on a txv system could mean the txv is not opening enough.