TM 5-3805-280-24-1
Theory of Operation
HEATER CIRCUIT (MACHINES WITHOUT AIR
CONDITIONER) OPERATIONAL
INFORMATION
The key switch must be in the ACC or On position for the
heater circuit to function.
CED,OUTX782,3 1918NOV981/1
HEATER CIRCUIT (MACHINES WITHOUT AIR
CONDITIONER) THEORY OF OPERATION
Power from the F13 Blower Motor 20 amp Fuse is applied
to the plus (+) terminal of the S4 Heater Blower Motor
Switch. On machines equipped with air conditioner, power
is also applied to the X16 Air Conditioner Harness to Cab
Harness Connector.
Power from the blower motor switch is applied through R2
Heater Blower Motor Dropping Resistor Block. The
resistor block applies different voltages to the motor,
depending on the blower speed selected. For low speed,
power is applied through the maximum resistance,
resulting in the lowest voltage. For high speed, the
resistors are bypassed and full voltage is applied to the
motor. Motor ground is applied to the minus (-) motor
terminal.
9031
05
6
CED,OUTX782,4 1918NOV981/1
7-6
