BENDIX BW1779 Fascicule

Air system leakage (See Common Test 4)
Compressor head gasket failure
– Apply soap solution around cylinder head.  If leakage between head

and block noted repair or replace comp.

This complaint  caused by leakage, either Service system or Supply
system. Service system leakage is shown on dash gauges. Supply
system leakage is not.  Note: System purge air dryers will purge more
often than those with integral purge volume.
Service system leakage (See Common Test 4)
Supply system component leakage
Drain system, install gauge and shop air hose in place of drain cock
in supply reservoir. Fill system to 120 psi, shut off shop air and check
leakage on following components in order presented.
– Comp. unloader leakage
– Drain system, remove governor from comp. plug governor UNL port

and re-test. If leakage OK repair comp. unloader mechanism or
replace comp. If leakage NOT OK then next.

– Holset ECON valve (used with Holset Type “E & QE” comp.)

missing, malfunctioning, leaking

– Is ECON valve required but missing? If YES, install, along with

special Holset check valve w/choke.  If NO and ECON valve present
replace ECON valve and special check valve. If NO and ECON not
required then next

– Air dryer leakage
– Remove line from air dryer inlet and with 120 psi in supply res. soap

exhaust and inlet port of air dryer. If leakage greater than 1 inch
bubble in 1 second at exhaust port, repair or replace check valve (on

dryers with integral purge volume) or replace body assy. on system
purge air dryers. If leakage greater than 1 inch bubble in 1 second
at inlet port, repair or replace purge valve assy. (on dryers with
integral purge volume) or replace turbo cut-off valve on system
purge air dryers

Drain air system to 0 psi, remove/disconnect governor from comp.
Start engine and note air pressure rise on dash gauges.  Apply 120 psi
shop air to comp. unloader port.  If air pressure continues to rise, repair
comp. unloaders or replace comp. If air ceases to rise, repair or
replace governor.

Brakes out of adjustment
– Adjust brakes
Excessive system leakage on service (application) side of system
– Build system pressure to 120 psi and shut off engine.  With park

brakes released, make full service application and note dash
gauges for 2 minutes. Pressure drop on either gauge should not
exceed 4 psi. (2 psi per min.) If pressure drop excessive, find
leakage in service system, if OK, then next.

Incorrect low pressure switch in use or setting incorrect
– Build system to 120 psi.  Engine OFF ignition ON, slowly drain air

pressure from one service reservoir. Low pressure warning on at
minimum 60 psi, maximum 10-15 psi less than governor cut-in
pressure.

Discharge line plugged or restricted (See Common Test 1)
Air pressure trapped between governor and compressor
unloaders (See Common Test 2)
Blow Leakage at Air Dryer Exhaust (See Common Test 3)

Discharge line restricted (See Common Test 1)
Discharge line leakage (See Common Test 5)
Air Leaking at Air Dryer Exhaust (See Common Test 3)
Compressor head gasket failure
– Apply soap solution around cylinder head.  If leakage between head

and block noted repair or replace comp.

Air pressure trapped between governor and compressor
unloaders (See Common Test 2)
Air system leakage  (See Common Test 4)

Blow leakage at compressor unloaders
– Remove all hardware from comp. inlet then remove governor.  With

120 psi shop air applied to comp. unloader port listen for leakage at
inlet.  If noted, repair leak or replace comp.

Incorrect setting on governor
– Verify Safety Valve operation. Drain air from system, remove or

disconnect governor from comp. and install gauge in governor
unloader (UNL) port. Build system pressure and note when pressure
on dash gauge and test gauge are equal. Should be equal at
maximum setting of governor.

Discharge line leakage (See Common Test 5)

– Connect temporary discharge line from comp. discharge port to

supply res. & re-check build-up. If build-up OK replace plugged
discharge line. If build-up NOT OK go to next cause.

– Verify Safety Valve operation then remove or disconnect governor

from comp. & check build-up.

– If build-up OK, repair or replace governor or line between gov. and

comp.

– If build-up NOT OK repair or replace comp.

– Drain all air from Supply reservoir then remove control air line from

Air Dryer, plug line and plug control port in Air Dryer.  Re-check build-
up.

– If build-up OK, repair or replace governor or line between governor

and Air Dryer

– If build-up NOT OK, and below 32 deg. F, turn ignition ON and allow

heater to warm Air Dryer then check build-up.  If NOT OK, remove
wire (connector or terminal) from Air Dryer. Using test light, check
wire end or terminal for battery voltage with vehicle ignition ON.
If voltage OK, repair or replace Air Dryer heater and thermostat. If
voltage NOT OK, Repair or replace the vehicle wire connected to Air
Dryer. Retest build-up.

– If build-up still NOT OK or temp. above 32 deg. F, replace Air Dryer

purge valve assembly.

– Build system pressure to governor cut-out, wait 2 minutes for dryer

purge completion. Note pressures on dash gauges then watch dash

gauges for 2 minutes. Leakage not to exceed 2 psi in 2 mins. for
truck, bus, tractor (no trailer).

– If leakage NOT OK on gauges, find leak(s) in service and park

system and repair. Retest and if system purge air dryer in use and
still not OK repair or replace dryer.

– If leakage OK on gauges, drain air from supply reservoir, remove

drain cock and install air gauge.  Build system air in supply reservoir
and note leakage.  If OK continue checking.  If NOT OK find leaks
and repair.

– Soap cover on flex discharge line, if leakage noted replace line
– Soap fittings to check leakage, tighten as needed

IMPORTANT:  The Complaints, Causes and Remedies presented here should not be considered as the only situations possible.  They are only meant to represent the most commonly encountered.  It may be necessary
to perform additional trouble shooting using the more detailed information presented in service manuals for the specific components.