To test the parking brake, you should have the trailer air supply in, trailer hand brake released, and the parking brake _________?

Here are the steps to test the parking brake:
1. Set the trailer air supply to in.
2. Release the trailer hand brake.
3. Set the parking brake.
4. Try to move the trailer. If the parking brake is working properly, the trailer should not move.
If the trailer moves, the parking brake may need to be adjusted or repaired.