TM-9-2320-272-10
TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL)
TECHNICAL MANUAL; OPERATOR'S MANUAL
SEPTEMBER 2004
CHANGE 2
TM-9-2320-272-10 - Page 70 of 481
TM 9-2320-272-10
1-53
K
CIRCUIT BREAKER
– Provides overload protection for 12-volt circuit 569A
leading to heater switch.
L
BATTERY SWITCH
– Provides 12-volt battery power from circuit 569
through 569A to the heater.
G
HEATER BLOWER MOTOR
– A direct current motor controlled by the
heater switch through circuit 400.
H
PROTECTIVE CONTROL BOX
– Provides 24-volt power to circuit breaker
through circuits 5 and 5a and to the heater switch through circuits 27 and 5c.
I
CIRCUIT BREAKER
– Provides overload protection for 24-volt circuits 5,
5a, 27, and 5c leading to the heater switch.
J
HEATER SWITCH
– Controls low and high blower motor speed and has two
sources of power; 12-volt power is supplied through circuit 569A from the
battery switch and is used to provide low speed; 24-volt power is supplied
through circuit 5C from the protective control box and is used to provide high
speed.
1-19. ELECTRICAL SYSTEMS OPERATION (Contd)
f. Heating System Operation.
The electrical portion of the heating system is identical for all models covered
in the manual and consists of the following major components and circuitry:
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