Hino 600, Workshop Manual, Page: 285 / 451

SERVICE BRAKE (FULL AIR BRAKE) BR02–7
OPERATION & LEAKAGE TESTS (ALSO SEE VIDEO BW2327)
.
1. Check all lines and fittings leading to and from the air dryer and reservoir system for leakage and integrity. Repair any
leaks found.
2. Build up system pressure to governor cut-out and note that the AD-IS

air dryer and reservoir system purges with an
audible escape of air. Watch the system pressure and note the pressure fall-off for a ten minute period. If pressure drop
exceeds, for a single vehicle - 1 psi/minute from either service reservoir; or for tractor trailer - 3 psi/minute from either ser-
vice reservoir, inspect the vehicle air systems for sources of leakage and repair them. Refer to section entitled Trouble-
shooting, Symptoms 1 and 4.
3. Caution: Be sure to wear safety glasses in case of a purge blast. Check for excessive leakage around the purge
valve with the compressor in the loaded mode (compressing air). Apply a soap solution to the purge valve exhaust port
and observe that leakage does not exceed a 1" bubble in 1 second. If the leakage exceeds the maximum specified, refer
to section entitled Troubleshooting, Symptom 4.
4. Build up system pressure to governor cut-out and note that the AD-IS

air dryer and reservoir system purges with an
audible burst of air, followed immediately by approximately 30 seconds of air flowing out of the purge valve. "Fan" the ser-
vice brakes to reduce system air pressure to governor cut-in. Note that the system once again builds to full pressure and
is followed by an AD-IS

air dryer and reservoir system purge. If system does not follow this pattern, refer to section enti-
tled Troubleshooting, Symptoms 5 and 6.
5. Check the operation of the end cover heater and thermostat assembly during cold weather operation as follows:
.
a. Electric Power to the Dryer
With the ignition or engine kill switch in the RUN position, check for voltage to the heater and thermostat assembly using
a voltmeter or testlight. Unplug the electrical connector at the air dryer and reservoir system and place the test leads on
each of the connections of the female connector on the vehicle power lead. If there is no voltage, look for a blown fuse,
broken wires, or corrosion in the vehicle wiring harness. Check to see if a good ground path exists.
b. Thermostat and Heater Operation
NOTICE
These tests are not possible except in cold weather operation.
Turn off the ignition switch and cool the thermostat and heater assembly to below 40 degrees Fahrenheit. Using an ohm-
meter, check the resistance between the electrical pins in the air dryer and reservoir system connector half. The resis-
tance should be 1.5 to 3.0 ohms for the 12 volt heater assembly and 6.0 to 9.0 ohms for the 24 volt heater assembly.
Warm the thermostat and heater assembly to approximately 90 degrees Fahrenheit and again check the resistance. The
resistance should exceed 1000 ohms. If the resistance values obtained are within the stated limits, the thermostat and
heater assembly is operating properly. If the resistance values obtained are outside the stated limits, replace the heater
and thermostat assembly.
6. Pressure Protection Valves. Observe the pressure gauges of the vehicle as system pressure builds from zero. The pri-
mary or secondary gauge should rise until it reaches approximately 106 p.s.i. (6 p.s.i.), then level off (or a momentary
slight fall) as the next pressure protection valve opens supplying its reservoir. When that pressure gauge passes through
approximately 106 p.s.i. (6 p.s.i.) there should be an associated leveling off (or momentary slight fall) of pressure as the
third and fourth pressure protection valves open. Then the primary and secondary gauges should increase together until
they reach their full pressure of approximately 130 psi (5 psi).
If the AD-IS

air dryer and reservoir system does not perform within the pressure ranges as described above, recheck
using gauges known to be accurate. If the readings remain outside of the ranges outlined above, replace the AD-IS

air
dryer and reservoir system. NOTE: There are no kits available for the servicing of the pressure protection valves. WARN-
ING: Do not attempt to adjust or service the pressure protection valves - incorrect pressure protection valve set-
tings can result in automatic application of the vehicle spring brakes without prior warning
in the event one of
the supply circuits experiences rapid pressure loss.