Which component controls the air compressor cut-in pressure?

• A. Air governor
• B. Pressure relief valve
• C. Intake filter
• D. Fuel pressure regulator

Answer: (A)

The air governor is the device that controls when the air compressor starts by sensing the system’s air pressure. When the pressure drops to the lower limit, the governor allows the compressor to start pumping air (cut-in). As pressure rises to the upper limit, the governor stops the compressor to prevent over-pressurization (cut-out). This keeps the brake system ready with enough air while avoiding unnecessary compressor run time.

The other components serve different roles: a pressure relief valve protects against overpressure but doesn’t control when the compressor starts; an intake filter cleans incoming air but doesn’t regulate compressor cycling; a fuel pressure regulator manages engine fuel pressure, not air system pressure.