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TM 5-4120-270-15
densation. A system of solenoid and expansion valves
directs the liquid refrigerant to the evaporator coil for
conditioned
area
cooling.
When
the
desired
temperature is attained, the same valves bypass the
evaporator coil to prevent further cooling of the
conditioned
area.
The
compressor
operates
continuously whenever the selector switch is on "COOL"
to prevent voltage fluctuations in the power line. A time
delay relay keeps the hot gas bypass valve open and
prevents operation of the compressor for 30 seconds
after initial startup.
Note. Hot gas bypass solenoid valve V, remains at all
time during cooling cycle and bypass cycle operation. It
opens when selector switch is moved from "COOL"
position ad remains open for 30 seconds after selector
switch is returned to "COOL" position.
c.
Cooling Cycle of Operation. When the
conditioned
area
temperature
rises
above
the
temperature control thermostat setting, a set of contacts
opens, permitting liquid line solenoid valve V, to return to
its normally open position. Liquid refrigerant is metered
to the evaporator coil by thermal expansion valve W1.
Thermal expansion valve W, bypasses a small amount
of liquid refrigerant to the suction line to maintain a
constant load on the compressor. The back pressure
,regulating valve (BPR) prevents evaporator coil icing
and loss of efficiency. The condenser receiver and
accumulators further stabilize the system.
d.
Bypass Cycle of Operation. When the
conditioned
area
temperature
falls
below
the
temperature control thermostat setting, a set of contacts
closes, energizing the pull-in coil of liquid line solenoid
valve V, and blocking the flow of liquid refrigerant to the
evaporator coil. Suction pressure increases and the
back pressure regulating valve (BPR) opens to bypass
hot refrigerant gas to the suction line. At the same time,
thermal expansion valve W, meters increased amounts
of liquid refrigerant into the suction line to maintain a
constant load on the compressor. The condenser
receiver and accumulators further stabilize the system.
e.
Heating Operation. Placing the selector
switch in the "LO HEAT" position actuates half of the
evaporator heaters mounted in the conditioned air
stream, directly behind the evaporator coil. When the
selector switch is placed in the "HI HEAT" position, the
remaining heaters are energized, providing maximum
heating capacity.
5-17.
Cover Panel
a.
Removal. Refer ’to figure 3-8 and remove
cover panel.
b.
Installation. Refer to figure M8 and install
cover panel.
5-18.
Control Panel
a.
Removal. Refer to figure 5-2 and remove
control panel.
Note. Use care in removing temperature control
thermostat remote bulb and capillary tubing.
b.
Installation. Refer to figure 5-2 and install’
control panel.
5-19.
Junction Box
a.
Removal. Refer to figure 5-2 and
remove junction box.
b.
Installation. Refer to figure 5-2 and
install junction box.
5-20.
Electrical Heaters and High
Temperature Cutout
a.
Removal. Refer to figure 5-8 and
remove electrical heaters and high temperature cutout.
b.
Installation. Refer to figure 58 and
install electric heaters and high temperature cutout.
5-21.
Evaporator Fan Motor
a.
Removal. Refer to figure 3-15 and remove
evaporator fan motor.
b.
Installation,. Refer to figure 315 and install
evaporator fan motor.
5-22.
Sight Glass
a. Removal. Refer to figure 54 and remove sight glass.
b. Installation. Refer to figure 5-4 and install sight glass.
5-23.
Evaporator Coil
a.
Removal. Refer to figure 55 and remove
evaporator coil.
b.
Installation. Refer to figure 55 and install
evaporator coil.
5-24.
Compressor
a.
Removal. Refer to figure 56 and remove
compressor.
b.
Installation. Refer to figure -6 and install
compressor.
5-25.
Expansion Valves
a.
Removal. Refer to figure 5-7 and remove
expansion valves.
Note.
Use care in removing remote sensing
bulb and capillary tubing.
5-4
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