Level when running it IF Stationary/Parked.
Running it while driving os OK because the movement of truck/rig keeps coolant flowing.
Bypassing the control board by unplugging the 120V AC element leads from bard and plugging them directly into a 120V AC outlet is a method used to test if cooling unit works. Plugged directly in the element heats continuously causing cooling unit to flow without any shutting down. IF cooling unit is working properly then the freezer section will go to at least 0*F (or lower) and food compartment temps will be 38*F (or lower...possibly down to 32*F)
Does NOT hurt or cause any damage.
IF cooling unit has blockages then 'test' will show.....freezer temps good/food compartment temps warm. Bad cooling unit---replace
After 4 hours freezer section should show signs of cooling...after 8 hrs food compartment----after 12 hrs temps in both S/B cold.
With rig level and leads plugged back in.....you should see cooling by this evening and fully reach temps by tomorrow AM.
Temp set point at MAX
Good luck!