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ARMY TM 9-4120-381-14
NAVY EE-000-CA-MMA-010/7053-AC
AIR FORCE TO 35E9-136-31
1-11. SAFETY, CARE, AND HANDLING. Read and understand all instructions relating to the specific function you are
to perform before starting task.
a.
Carefully read and understand all notes, cautions, and warnings contained in this manual that pertain to the task
you are to perform.
b.
Carefully read and understand all WARNING and CAUTION plates located on the air conditioner.
c.
Never operate the air conditioner with any covers, air filters, or panels removed unless the instructions
specifically instruct you to do so. Then do so only with extreme caution.
d.
Carefully plan all maintenance tasks and never take unnecessary risks.
Section III. TECHNICAL PRINCIPLES OF OPERATION
1-12. SCOPE. This section tells how the air conditioner works in its various configurations and operating cycles (see
Figure 1-5).
1-13. OPERATING CONFIGURATIONS. This air conditioner can be operated as either a redundant, remotely
controlled unit or as a single, locally controlled unit. Two separate control systems are provided in the air conditioner for
these configurations.
a.
Redundant Unit, Remote Control Configuration. In this configuration, the air conditioner is paired with at least
one other air conditioner and controlled from a remotely located control panel. The air conditioner MODE
SELECT SWITCH must be positioned to REMOTE. When cooling is remotely selected, a pressure regulator
valve (V3) is used to control supply air temperature. When heating is remotely selected, a heat control
thermostat located in the return air section of the air conditioner monitors the return air and controls the electric
heaters. The heat control thermostat shuts off the electric heaters when the return air reaches 80°F (27°C). The
remote control operation modes can be overridden at any time by LOCAL mode selections on the air conditioner
MODE SELECT SWITCH.
b.
Single Unit, Local Control Configuration. Operation of the air conditioner as a single, stand alone unit requires
the installation of three jumper wires on terminal board TB2 and opening the manual bypass valve (V7). With
the pressure regulator valve (V3) bypassed, cooling control is performed by the cycling of a solenoid valve (L1)
located in the refrigerant line upstream of the primary expansion valve (V12). A cool control thermostat located
in the return air section of the air conditioner will deenergize the solenoid valve (L1) when the return air drops
below the nominal set point of 70°F (21 °C). This thermostat also provides automatic heat/cool changeover.
1-14. OPERATING CYCLES. Normal operation of this air conditioner includes cooling, bypass, and heating cycles.
These cycles are described in the following paragraphs, with explanations added for different modes of operation.
a.
Cooling Cycle. Air conditioner operation when cooling is initiated.
(1)
Evaporator fan (B1), compressor (B2), and condenser fan (B3) start.
(2)
The compressor (B2) receives low pressure superheated refrigerant gas and compresses it to a high
pressure, high temperature gas. This gas flows through metal tubing to the condenser coil (C).
(3)
The condenser fan (B3) draws outside ambient air over and through the condenser coil (C). The high
pressure, high temperature gas from the compressor (B2) is cooled by the flow of air and condensed into a
high pressure liquid. If ambient air temperature increases, the gas entering the condenser coil (C) will
increase in pressure, causing the condenser fan damper actuator (A) to open the damper and allow an
increased flow of air across the condenser coil (C).
(4)
The receiver (R) stores excess refrigerant during periods of decreased load or low ambient temperature, or
during maintenance pump down procedures.
(5)
The high pressure liquid from the condenser is subcooled by the tube-in-tube heat exchanger (H), which at
the same time superheats the low pressure refrigerant gas returning to the compressor (B2).
(6)
A drier filter (F1) removes any moisture (water vapor) or dirt that may be carried by the refrigerant leaving
the heat exchanger (H).
1-7
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