Most commercial vehicles and large diesel housecars use Air Brakes to stop. As part of the Pre-trip inspection test for a CDL, a driver must demonstrate knowledge of how an Air Brake system works and how to check it. Noncommercial Class B applicants are not required to pass this portion of the test, but all Class B Boot Camp Grads will be proficient in the Air Brake Test.

To check an Air Brake system, the driver is expected to perform an in-cab air check or as it is known in California, 
A COLA check.

C stands for COMPRESSOR CUT IN: The Governor will cause the air compressor to Cut In and start pumping, when the pressure in the system drops to between 85 – 105 psi, as indicated by the air gauges. When the air gauge needles rise the driver knows the air compressor pump is working.

O stands for COMPRESSOR CUT OUT: The air compressor, shown in the diagram above will pump air until the system is fully charged, 120 – 130 psi, at which time the Governor will cut out the pump and you will hear an air blow off. (Psssh).

L stands for LOW AIR WARNING: All Air Brake equipped vehicles are required by law to have an audible and a light warning system to alert the driver, should air pressure fall to 55 – 75 psi. This is important information for the driver because if the air pressure were to fall below 45 psi, the brakes in the vehicle will immediately be fully applied!

A stands for APPLIED AIR LEAKAGE TEST: The purpose of this test is to ensure the system is secure and has no leaks. With a fully charged air system and the vehicle securely parked, the driver releases the parking brake, turns off the engine, presses and holds the brake pedal to the floor for 1 minute, making sure the system does not lose more than 3 psi. When finished, the driver indicates to the examiner there was no air pressure loss and applies the parking brake.

PRACTICAL BRAKE TEST:

Parking Brake Test, with the parking brake on, put the coach in gear to see if it holds.

Service Brake Test, release all brakes pull coach forward about five feet, apply service brake making sure the coach stops smooth with no pulls in either direction.