The assigned truck has an air compressor with a separate oil supply. Its engine-oil check is satisfactory. Which item still belongs in the pre-trip check?
Correct answer: The oil level in the compressor's separate supply
The manual distinguishes a compressor's own oil supply from engine-supplied lubrication. A satisfactory engine-oil reading does not establish the level in the separate compressor supply.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System, Version July 2014; Section 5 > 5.1.1 - Air Compressor; printed5-1, physical77. Current NCDMV-linked copy reviewed September 13, 2026. ↗
An equipment checklist identifies this truck's air compressor as belt-driven. Which observation is specifically relevant to that drive arrangement?
Correct answer: Whether the compressor belt is sound and properly tensioned
A belt-driven compressor needs a belt-condition and tightness check. The qualification matters: some compressors are gear-driven, so this is not a universal compressor-belt requirement.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System, Version July 2014; Section 5 > 5.3.1 - During Step 2 Engine Compartment Checks; printed5-6, physical82. Current NCDMV-linked copy reviewed September 13, 2026. ↗
A stationary truck's reservoir pressure reaches its specified upper setting and stops rising while the engine continues to run. Later, the compressor resumes adding air at the specified lower setting. What does this sequence demonstrate?
Correct answer: The governor is controlling compressor pumping
The governor controls when the compressor pumps into the reservoirs. Cut-out and cut-in are pressure-based operating points; their actual values must be checked against the manufacturer's specifications.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System, Version July 2014; Section 5 > 5.1.2 - Air Compressor Governor; corroborating 5.3.3 on physical83/printed5-7; printed5-1, physical77. Current NCDMV-linked copy reviewed September 13, 2026. ↗
In a safely secured training vehicle, the compressor has stopped, but the charged air system can still make brake applications. What accounts for this?
Correct answer: The reservoirs retain a limited supply of compressed air
Reservoirs store compressed air, so applications can remain possible after the compressor stops. The stored supply is finite; this is not permission to drive with a failed compressor.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System, Version July 2014; Section 5 > 5.1.3 - Air Storage Tanks; printed5-1, physical77. Current NCDMV-linked copy reviewed September 13, 2026. ↗
At the end of a driving day, a truck with manual-only reservoir drains shows normal air pressure. Why does that reading not justify skipping the specified draining?
Correct answer: Water and oil can remain in tanks that show normal pressure
A supply gauge shows pressure, not whether water and compressor oil have collected at the bottom of a reservoir. The manual calls for end-of-day drainage on systems without automatic drains.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System, Version July 2014; Section 5 > 5.1.4 - Air Tank Drains; corroborating 5.4.8 on physical85/printed5-9; printed5-1, physical77. Current NCDMV-linked copy reviewed September 13, 2026. ↗
A truck's automatic reservoir drain includes an electric heater. What is that heater intended to protect against in cold weather?
Correct answer: The automatic drain freezing
Some automatic drains have electric heaters to help prevent the drain from freezing. That is a drain-system feature, not a means of warming friction linings or controlling governor settings.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System, Version July 2014; Section 5 > 5.1.4 - Air Tank Drains; printed5-1, physical77. Current NCDMV-linked copy reviewed September 13, 2026. ↗
This vehicle is equipped with an approved alcohol evaporator and manual-only reservoir drains. Its evaporator has been serviced according to the vehicle instructions. What follows?
Correct answer: The specified reservoir-draining routine still applies
On a system fitted with an alcohol evaporator, its ice-prevention role does not remove collected water and oil from manually drained reservoirs. This does not advise adding alcohol to a system that is not designed for it.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System, Version July 2014; Section 5 > 5.1.5 - Alcohol Evaporator; printed5-2, physical78. Current NCDMV-linked copy reviewed September 13, 2026. ↗
During an air-system check, the reservoir safety relief valve releases air because pressure has become excessive. What is the appropriate conclusion?
Correct answer: The pressure-control fault needs qualified attention
The safety valve protects the system from excessive pressure. Its release is a warning of a fault to be corrected, not evidence of a completed brake test or a reason to alter its setting.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System, Version July 2014; Section 5 > 5.1.6 - Safety Valve; printed5-2, physical78. Current NCDMV-linked copy reviewed September 13, 2026. ↗
While waiting in traffic, a driver needlessly presses and releases an air-brake pedal over and over. Why can this reduce the available braking reserve?
Correct answer: Each release exhausts air that the compressor must replace
Air is exhausted as service brakes release. Unnecessary repeated applications can use air faster than the compressor replaces it. This is a warning against needless cycling, not an instruction for emergency braking.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System, Version July 2014; Section 5 > 5.1.7 - The Brake Pedal; printed5-2, physical78. Current NCDMV-linked copy reviewed September 13, 2026. ↗
In a cutaway of an S-cam drum brake, the chamber pushrod moves the slack adjuster and turns the camshaft. What should the turning S-cam do next?
Correct answer: Spread the shoes against the inside of the drum
In the S-cam design, cam rotation moves the brake shoes outward against the drum. The question concerns the illustrated mechanism, not an adjustment procedure or every air-brake design.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System, Version July 2014; Section 5 > 5.1.8 - Foundation Brakes > S-cam Brakes; Figure5.2; printed5-2, physical78. Current NCDMV-linked copy reviewed September 13, 2026. ↗
A technician identifies the wheel brake being inspected as an air-operated disc brake, not a drum brake. Which friction arrangement should the trainee expect?
Correct answer: A rotor gripped between pads in a caliper
Disc brakes slow the wheel by clamping a rotor between friction pads. This item does not generalize the manual's older actuator description to every current air-disc brake model.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System, Version July 2014; Section 5 > 5.1.8 - Foundation Brakes > Disc Brakes; printed5-2, physical78. Current NCDMV-linked copy reviewed September 13, 2026. ↗
A truck has reservoir supply gauges and a separate application-pressure gauge. With the service pedal released, the supply gauges show charged tanks but the application gauge is near zero. How should these readings be understood?
Correct answer: Stored air pressure can be present without a service-brake application
Supply gauges show pressure available in the reservoirs; an application gauge shows pressure being applied to the brakes. They measure different things, so their readings need not match.
Source: North Carolina Commercial Driver License Manual, 2005 CDL Testing System, Version July 2014; Section 5 > 5.1.9 - Supply Pressure Gauges; 5.1.10 - Application Pressure Gauge; printed5-2, physical78. Current NCDMV-linked copy reviewed September 13, 2026. ↗
