This short video shows a bite check on the nitrogen generation system on a 737NG. The system was degraded and needed troubleshooting. Not all procedures of the troubleshooting are shown, only the bitecheck part and the movement of the high flow valve.
For complete troubleshooting always use the FIM and AMM procedures.
Also, during the bite check, the LH airco pack needs to be on for at least 10 minutes in high mode.