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TM 5-4120-287-15
heating capacity of 35,000 BTU/hr (10.5 kw (kilowatts)). The air conditioning unit is contained in a single enclosure of
compact sturdy construction built to rigid military specifications and standards. The enclosure is subdivided into a
condenser section and evaporator section. The condenser section contains the compressor, condenser fan, and high-
pressure refrigerant controls. The evaporator section contains the evaporator, evaporator fan, expansion valve, heaters,
electrical controls, and temperature controls. Functionally, the air conditioning unit consists of a cooling subsystem and a
heating subsystem regulated by either automatic or manual controls from a remote control box.
b. Electrical Tray Assembly. The electrical tray assembly (fig 1-3) contains the electrical power controls and
relays. The front panel of the electrical tray assembly contains the circuit breaker, the system reset push button, the
hourmeter, the control circuit fuse, the main power connector, and the remote control box assemble connector. Mounted
within the electrical tray assembly are the motor control relays, the temperature control relays, the transformer, the phase
sequence relay, and the rectifier. The 28-vdc (volts direct current) power required for the operation of the relays is
obtained from the transformer and the rectifier.
c. Remote Control Box Assembly. The remote control box assembly (fig 1-1) contains the operating controls for
the air conditioning unit. Mounted on the front panel is a four-position (HEAT, OFF, VENT, COOL) five-deck switch and a
temperature control variable resistor (minimum setting COOL; maximum setting HEAT). The rheostat dial is continuously
variable between the COOL and WARM positions, which corresponds to a return air temperature range of 60F to 90F.
d. Motor-compressor. The motor compressor (fig 1-4) consists of positive-displacement compressor which is
directly driven by an integral 8-hp, 416-volt, 400-cycle, 3-phase, 4-wire induction motor with a designed speed of 7700 rpm.
The compressor draws low pressure refrigerant vapor from the evaporator and compresses it to a high pressure, high
temperature refrigerant vapor. The motor-compressor runs continuously when the air conditioner is operating in the COOL
mode.
e. Thermostat. The thermostat (fig 1-3) is located in the evaporator compartment. The thermostat senses the
temperature of the air entering the evaporator and provides control signals to maintain desired temperatures.
f. High-low Pressure Cut-out Switch. The high-low pressure cutout switch (fig 1-4) is a dual single pole, single
throw switch which projects the cooling system from excessive compressor discharge pressure and low compressor inlet
pressure. The high-pressure side of the switch is connected into the compressor discharge line; the low pressure side into
the compressor inlet line. The switch has a rating of 2 amperes at 28 vdc. The high pressure side is set to close the
switch (energizing the trip relay, which removes power from the compressor) when the pressure in the compressor
discharge line increases to 260 to 265 psig (pounds per square inch gage). The switch will automatically reset when the
discharge line pressure decreases to 200 to 220 psig. The low-pressure side is set to close the switch when the pressure
in the compressor inlet line decreases to 20 to 21 psig. The switch will automatically reset when the inlet line pressure
increases to 30 to 40 psig. The system trip relay is reset by pressing the system RESET switch (fig 1-3).
g. Condenser Fan. The condenser fan assembly (fig 1-5) provides cooling air for the condenser. As supplied, it
is complete with its own bearings and seals and is permanently lubricated. The fan is a high-speed (5800 rpm) continuos
duty, vane-axle type with a self-contained motor for use on 416-volt, 3-phase, 400-cycle, 4-wire power. The condenser fan
is rated at 4120 SCFM (Standard Cubic Feet/Minute). The fan motor is constructed with an internal automatic reset
thermal and overcurrent protector.
Note
The condenser fan discharge door must be open when unit is operating in cooling cycle. A Microswitch,
activated by the door, prevents operation of compressor motor and condenser fan motor if door is closed.
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