Air brake testing

Testing the Air Brakes |  Pre-Trip Inspection | Brake Check

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If you own a motorhome with air brakes you should test the system to ensure that everything is working properly. Do you know how?

Most, if not all, never really know what is involved in how the air system controls the braking system and how important it is to know what to look for if the warning alarm does sound. So first lets briefly describe how the system works.

All air brake systems use air pressure to apply the brakes when you step on the pedal. The pressurized air is stored in a series of air tanks on the motorhome. The air is pressurized by the air compressor on the RV's engine. The pressure is regulated by the D2 air governor, most, if not all systems, work on 120 psi of pressure.

The air is then sent through an air dryer, which removes the moisture from the air to keep it from freezing in the winter and from causing general corrosion. The air dryer has a cartridge in it that must be changed on a regular basis or the desiccant will break down and contaminate the air system.

Air brake test should be conducted before every trip in your RV.  Here is a quick checklist on how to test the air and brake systems.  First You should be on level ground with the wheels chocked for some parts of this check.

• Low air warning system test.  Start the engine and build up pressure, turn engine off, turn ignition switch back on, pump brake pedal to reduce air pressure until warning light and beeper comes on. (This should happen at about 60 psi.)
• Emergency/parking brake test. Push brake knob in, continue reducing air pressure by lightly pumping the breaks. The yellow parking brake knob should "pop out" to indicate the parking spring brake (Maxi brake) has been activated (25-35 psi). Start engine let air pressure build up until low air pressure warning beeper stops (70-80 psi). Push parking brake knob in & attempt to move coach forward. Should move freely without any brake drag.
• Air pressure build up test. Continue to let the air pressure build; it should not take more than four minutes for the air pressure to go from discharged (5-20 psi) to between 120 and 130 psi.
• Governor cut-in/cut-out test. When air pressure gets between 120-130 psi, the governor should cut out. The dash gauge needle stops moving. When the needle stops, pump the brake pedal to reduce the air pressure to 80 psi, release the brake pedal, the compressor starts pumping air (cutting in)! watch for needle movement. The air governor causes the air compressor to cut in between (85-90 psi).
• Air leak test. Stop engine, parking brake on, and transmission in neutral. The air pressure must not drop more than 2 psi in the first minute. Release the parking brake; the air pressure must not drop more than 2 psi in this second minute. Apply service brake and hold it. The initial pressure drop must not be more than 10 psi. Continue to hold the pedal down for one full minute. The pressure should not drop by more than 3 psi.

Now that you know how the system works normally, you will be able to quickly diagnose and respond quickly before any mishap could occur.