TM-9-2320-283-20-1
TRUCK TRACTOR, LINE HAUL, 50,000 GVWR, 6X4, M915A1
TECHNICAL MANUAL; ORGANIZATIONAL MAINTENANCE PART 1 OF 3
DECEMBER 1983
TM-9-2320-283-20-1 - Page 109 of 926
TM 9-2320-283-20-1
PRINCIPLES OF OPERATION.
1-23.
CAB HEATING AND VENTILATING SYSTEM.
BATTERY PACK.
Consists of four, 12-volt, maintenance free batteries.
Two batteries are wired in parallel in each set.
Each set is connected in series for 24-volt output.
Battery pack is used for both 12-volt and 24-volt output.
IGNITION SWITCH.
Supplies 24-volt power to relay (RY-9), which in turn provides 12-volt power to electrical system,
including cab heating controls.
RELAY (RY-9).
Energized by 24-volt power from ignition switch.
When energized, RY-9 supplies 12-volt power to circuit
breaker (CB-4).
CIRCUIT BREAKER (CB-4).
Protects electrical components of heater fan switch by opening when load exceeds 20
amperes.
May be manually reset by pressing CB-4 button in.
FAN SWITCH.
Four-position switch with three ON positions.
Supplies 12-volt power from circuit breaker (CB-4) to motor.
Current flow increases as switch is moved from LOW to MEDIUM to HIGH.
HEADLAMP SWITCH.
Supplies 12-volt power to heater lamp when switched to ON position.
HEATER LAMP.
Illuminates heater fan control.
HEATER CONTROL.
Allows driver to heat cab.
Connected by cable to water control valve.
DRIVER HEAT CONTROL.
Allows driver to open or close heat vent for driver side of cab.
Connected by cable to heat
control lever.
PASSENGER HEAT CONTROL.
Allows passenger to open or close heat vent for passenger side of cab.
Connected by
cable to vent control lever.
FRESH VENT CONTROL.
Allows driver to control fresh air vent on passenger side.
Connected by cable to vent control
lever.
RECIRCULATION VENT CONTROL.
Allows driver to recirculate cab air through heater.
Connected by cable to
recirculation control lever.
HEATER SHUTOFF VALVE.
Supplies coolant to control valve.
Manual shutoff handle allows complete cutoff of coolant
flow to heater.
HEATER SUPPLY HOSE.
Carries coolant from front water manifold, through control valve, to heater.
1-88
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