What is a potential cause of 'frozen air lines' in an air brake system?

Answer: B — Moisture in the air lines freezing at low temperatures

A potential cause of 'frozen air lines' in an air brake system is indeed the presence of moisture in the air lines that can freeze at low temperatures. When water vapor is present in compressed air within the brake lines, it can condense and form droplets. If the temperature drops sufficiently, these droplets can freeze, leading to blockages in the air lines. This freezing impedes the flow of air necessary for the proper operation of the brake system, potentially resulting in brake failure or reduced braking efficiency. Maintaining the air brake system requires ensuring that moisture is minimized, often through the use of air dryers and regular maintenance checks. Understanding the implications of moisture in air lines is critical for safe operations, especially in colder climates where freezing conditions are prevalent.