Which of the installation steps listed is necessary for the proper operation of the thermostatic expansion valve?

Correct Answer: Option C — Clean off oxidation from the surface of the suction line and sensing bulb with fine abrasive cloth or steel wool.

Removing oxidation and scale from the suction line and sensing bulb using fine abrasive cloth ensures optimal thermal conductivity and heat transfer between the pipe wall and the bulb, which is critical for precise system superheat regulation.