Troubleshooting guide

58
www.bendix.com 1-800-AIR-BRAKE (1-800-247-2725)
Section 9: Air Brake System Troubleshooting Tests
T
EST ONE
In this test we check the low pressure warnings,
pressure buildup and governor cut-out and cut-in.
Park the vehicle and chock the wheels.
1. Drain all reservoirs (air tanks) to 0 PSI.
2. Start the engine and run it at fast idle. Is the
low pressure indicator buzzer working?

OK

Not OK
Observe the low pressure warning dash warning light -
does it switch off at or above 60 PSI?

OK

Not OK
Note: Some vehicles have alternate indicator devices.
Also, on vehicles with antilock, the ABS indicator lamp
will also come on momentarily when ignition is turned
on.
Troubleshooting: If the low pressure warning light
or buzzer doesn't come on: (a) Check the wiring and/
or bulb, (b) Repair or replace the wiring, buzzer, bulb
or low pressure indicator switch(es) as needed.
3. Time how long it takes to build air pressure
from 85 PSI up to 100 PSI. Does this take
less than 40 seconds?

OK

Not OK
Troubleshooting: If build up time exceeds 40
seconds:
(a) Examine the compressor air strainer and clean or
replace as needed.
(b) Check for a restricted inlet line if the compressor
does not have a strainer, repair or replace as necessary.
(c) Check compressor discharge port and line for
excessive carbon (more than 1/16" coating). Clean or
replace as necessary.
(d) With the air brake system charged, engine off and
governor compressor in unloaded mode, listen for
leakage at the compressor inlet. If leakage can be
heard, apply a small amount of oil around the unloader
pistons. If no leakage is indicated, then the leakage is
through the compressor discharger valves.
(e) Check the compressor drive for slippage.
4. Check vehicle manufacturer’s recommen-
dation for full air tank pressure. Does the
governor cut-out at the correct pressure?
(Typically between 100-130 PSI)

OK

Not OK
Troubleshooting: If the governor cut-out is higher
or lower than specified by the vehicle manual:
(a) For adjustable governors, adjust using a temporarily-
installed gauge of known accuracy. If the vehicle has a
non-adjustable governor, replace it.
(b) See the Service Data sheet for the compressor to
verify that the unloader mechanism is operating
correctly before replacing governor.
5. Reduce reservoir (air tank) pressure by
repeatedly applying the service brakes until
the governor cut-in. Is the difference
between cut-in and cut-out pressure 25 PSI
or less?

OK

Not OK
Troubleshooting: A difference of less than 25 psi
indicates a malfunctioning governor. Replace the
governor.
Retest to check out all items repaired or
replaced.
Make all necessary repairs before proceeding to
Test Two.
Air Brake System Troubleshooting Tests
Please follow all standard safety precautions,
including, but not limited to, the general
precautions listed on page 4 of this handbook.