TM 9-4120-404-14
1-13. HEATING CYCLE. The air conditioner is equipped with a heating operation mode. When the mode selector switch
is set for HEAT the six heating elements, located in front of the evaporator coil, are energized. These elements are
protected from overheating by a thermal cutout switch.
1-14. LOGIC BOX ASSEMBLY AND MOTOR CONTROLLER ASSEMBLY. The electrical operations of the air
conditioner are controlled through the operation of an electronic logic box assembly and a motor controller assembly. The
primary functions of each of these components is as follows. Refer to Figure 1-4, Logic Box Assembly/Motor Controller
Assembly Interface Schematic for detailed description of current and signal flows for air conditioner operation.
Box Assembly provides the following functions.
a. Logic Box Assembly. The Logic
(1) Accepts signals from the control panel assembly mode selector switch and temperature selection control to
control the operation of the air conditioner.
(2) Provides start/run and stop/reset signals to the motor controller.
(3) Accepts fault signals from the motor controller and illuminates the appropriate fault indicator light on the
control panel assembly.
(4) Accepts control circuit fault signals, including low and high pressure cutout signals, motor thermal overload
signals, heater over temperature signals, and evaporator coil frost cutout switch signals and will illuminate the applicable
fault light.
b. Motor Controller Assembly. The motor controller assembly provides the following functions.
(1) Accepts nominal input power of 208 VAC, 3 phase, 50/60/400 Hz and provides outputs of 208 volts ac, 3
phase 60 hz and 12 volts dc power.
(2) Provides a "soft start" output to the air conditioner motors under all operating conditions.
(3) Provides power to the logic box assembly.
(4) Interfaces with the logic box assembly by:
(a) Accepting start/run and stop/reset signals from the logic box assembly.
(b) Providing separate signals to the logic box assembly for the following faults:
Over and under voltage in the input power source.
Over current in output power.
Over temperature of the motor controller assembly.
(5) Automatically shuts down in the event of over/under input power voltage, output over current, or over
temperature of the motor controller assembly.
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