Air Brake Maintenance, Troubleshooting, and Alcohol Evaporators
This domain tests daily maintenance, common air brake faults, and the alcohol evaporator used in cold weather. Kansas winter conditions make moisture and freezing questions especially relevant.
Daily maintenance
- Drain air tanks to remove water and oil.
- Check compressor build-up and governor operation.
- Check the low-pressure warning and spring brake application.
- Inspect hoses, chambers, and slack adjuster/pushrod travel.
- In cold weather, check the alcohol evaporator level daily.
Troubleshooting clues
- Pressure will not build: compressor, governor, slipping belt, or major leak.
- Pressure drops when the brake is applied: leak in the service side.
- Compressor runs constantly: leak or stuck governor.
- Oil in tanks: compressor passing oil; needs repair.
- Brake drag: slack adjuster, cam, or spring brake problem.
Alcohol evaporator
It adds alcohol vapor to the air system to prevent moisture in lines and valves from freezing. Use only approved alcohol, do not overfill, and remember that it does not replace draining tanks or fixing leaks.
Worked example
On a cold morning, brakes respond slowly and the gauge is normal. The evaporator is empty. Fill it with approved alcohol and drain the tanks. If oil appears in the tanks, the compressor is the likely source and the vehicle needs service.
Traps
- Using any alcohol rather than approved alcohol.
- Overfilling the evaporator.
- Treating the evaporator as a substitute for draining tanks.
- Ignoring oil in the tanks.
Key points
- Drain tanks daily; moisture causes freezing and corrosion.
- Oil in tanks points to a failing compressor.
- Constant compressor operation suggests a leak or governor fault.
- The alcohol evaporator prevents line freeze-up; use approved alcohol only.
- The evaporator does not replace draining tanks or repairing leaks.