MAINTENANCE OF THE HEMTT - OD1662 - LESSON 1/TASK l
batteries (4).
Power is distributed throughout the vehicle by the
wiring harnesses. The harnesses are interconnected by pin connectors.
Connectors are provided at the rear of the vehicle to supply the power
for towed loads.
A heavy duty starting motor (5) is mounted on the
engine flywheel housing and provides the cranking power necessary for
starting the engine. The voltage regulator (6) is mounted on the belt
driven alternator (7) and maintains a 24-volt level for battery
charging.
(4) Air Systems (figure 21 on the following page).
The air system
consists of an engine driven air compressor (1) and four air
reservoirs (2, 3, 4, and 5)(all vehicles except the M983). The M983
tractor vehicle has reservoirs 2, 3, 5, and 6.
The system includes
the necessary valves and air lines to control the vehicle's air
operated devices.
Pressurized air from the air compressor is passed
through the air dryer (7) to the quick build-up reservoir (2).
The
air dryer removes dirt and moisture from the pressurized air.
Air
from the reservoir goes to the throttle treadle (8). Depending on how
far the throttle treadle is depressed, 0 to 60 pounds per square inch
(psi) is supplied to the engine air throttle cylinder (9) and to the
transmission modulator (10).
This air pressure controls vehicle
speed.
Once the air pressure in the reservoir (2) rises above 75 psi, a valve
opens and allows reservoirs (3), (4, or 6), and (5) to be pressurized.
Air from reservoir 4 or 6 goes to the brake treadle valve (11). This
air controls the rear axle service brakes (12). Air pressure in this
system is shown by the red needle on the AIR PRESS gage (13).
Air
from the reservoir (3) goes to the brake treadle (11).
This air
controls the front axle service brakes (14).
Air pressure in this
system is shown by the green needle on the AIR PRESS gage (13). The
PARKING BRAKE valve (15) controls air from reservoirs (3 and 5) and
applies or releases the rear axle service (parking) brakes (12).
Reservoirs (3), (4 or 6), and (5) are interconnected in such a way
that if one reservoir fails, air would be supplied from whichever
reservoir is functioning to release the rear axle service (parking)
brake (12). If the air pressure falls below 60 to 70 psi, a buzzer
will sound, the AIR indicator (16) will light, and the rear axle
brakes will be applied.
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