Thomas SAF-T-LINER C2, Maintenance Manual

Page: 118 / 176

5. Check the operation of the end cover heater and
thermostat assembly during cold weather opera-
tion as follows:
5.1 Electric Power to the Dryer: With the igni-
tion in the ON position, check for voltage
to the heater and thermostat assembly
using a voltmeter or testlight. Unplug the
electrical connector at the air dryer and
place the test leads on each of the con-
nections 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 ex-
ists.
5.2 Thermostat and Heater Assembly Opera-
tion: 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°F
(4°C). Using an ohmmeter, check the re-
sistance between the electrical pins in the
air dryer connector half. The resistance
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.
NOTE: Some models of the AD–9 may
have a resistance reading of 1.0 to 2.5
ohms.
Warm the thermostat and heater assem-
bly to approximately 90°F (32°C) and
again check the resistance. The resis-
tance should exceed 1000 ohms. If the
resistance values obtained are within the
stated limits, the thermostat and heater
assembly is operating properly. If the re-
sistance values obtained are outside the
stated limits, replace the heater and ther-
mostat assembly.
42–07 Brake Lines and Fittings
Inspecting, Hydraulic
Brakes
Chock the tires, release the parking brake, and make
a full service brake application.
Replace damaged or leaking components, and
tighten loose fittings.
42–08 Brake Pedal Linkage and
Mounting Plate
Inspecting
Inspect the pedal, pedal linkage, and mounting plate
assembly for proper operation to ensure that any
problems believed to be valve-related are not actu-
ally mechanism issues.
42–09 Air Brake Inspecting and
Leakage Testing
IMPORTANT: There is no scheduled (Bendix) air
valve maintenance that requires disassembly of
the valve within the warranty period. If the valve
does not function while within the warranty pe-
riod, do not disassemble the part as this will
void the warranty.
If any of the tests in the following procedure fail,
refer to
Group 42 of the Saf-T-Liner C2 School
Bus Workshop Manual to test individual air
brake components and valves.
WARNING
Some steps in this operation require the parking
brakes to be released. Make sure the vehicle is on
a level surface and all tires are chocked. Failure to
do so could result in the vehicle rolling, causing
personal injury and/or vehicle damage.
1. Park the vehicle on a level surface, shut down
the engine, apply the parking brake, and chock
all tires.
2. Completely drain all air reservoirs.
3. Install accurate test gauges in the primary and
secondary reservoirs.
4. Start the engine and run it at a fast idle.
5. Record reservoir pressures when the low-
pressure warning turns off.
6. Record governor cutout pressure and air dryer
purge pressure.
7. Reduce service air pressure by applying and re-
leasing the service brakes several times, and
record the governor cut-in pressure.
Brakes
42
Saf-T-Liner C2 School Bus Maintenance Manual, November 2020
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