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TM 5-4120-270-15
5-10.
Reduced Heating Capacity
Probable cause
Possible remedy
Restricted air flow over
Clean mist eliminator and
evaporator
evaporator coil (para
(3-1-, air filters (para
3-9) and grilles and
screens.
Defective selector switch
Test selector switch
(para
(“LO HEAT” only)
6-2). Replace if
defective.
Defective temperature con
Test thermostat (para 6-
3).
trol thermostat
Replace
if
defective
Probable cause
Possible remedy
Defective or damaged heat
Test heaters (para 6-10).
er elements
Replace if damaged
or defective
5-11. Inoperative Compressor Crankcase Heater
Probable cause
Possible remedy
Defective or damaged heat-
ing element
Replace if damaged
or defective
Section III. RADIO INTERFERENCE SUPPRESSION
5-12.
General
Refer to TM 11-483 for definitions, purposes, source
and methods used to obtain proper radio frequency
interference suppression.
5-13.
Interference Suppression Components The
four air conditioner RFI filters (fig. 3-6) mounted on the
junction box, are 5 amp, 250- volt, feed-through units.
5-14.
Replacement of Suppression Components
a.
Removal. Refer to figure 3-7 and
remove radio interference suppression components.
b.
Testing. Test filters on a continuity tester;
replace defective RFI filters.
c.
Installation. Refer to figure 3-7 and install
radio interference suppression components by reversing
removal procedure.
Section IV. REMOVAL AND INSTALLATION OF MAJOR COMPONENTS OR AUXILIARIES
5-15.
General
The air conditioner, after it is started, is automatic in
operation.
The
relationship
of
the
automatic
components, controls, and instruments, is explained in
the operating cycle description for maintenance of the
air conditioner (para 5-16). A refrigerant flow diagram
(fig. 5-1) and practical wiring diagram (fig. 1-6) are
included to assist in the maintenance of the electrical
components, wiring harness, wire leads, and refrigerant
components.
Warning: Disconnect the air conditioner from
the
power
source
before
performing
any
maintenance on the components of the unit.
5-16.
Description of Operating Cycle
a.
General. The type and degree of air
conditioning provided by the unit is controlled by a five-
position selector switch and a temperature control
(temperature control thermostat).
(1)
On units with reciprocating piston
compressors the crankcase heater is in constant
operation.
(2)
Placing the selector switch in the HI-
HEAT position actuates the blower motor with both
banks of evaporator heaters being under the control of
the temperature control. If the air temperature falling
below the set point of the temperature control the control
contacts close, energizing the contactors which supply
power to the heaters through the normally closed
contacts of the heater high temperature cutout.
(3)
Moving the selector switch to the LO
HEAT position presents the same control sequence but
reduces the heating capacity of the unit by supplying
power to a single bank of heaters only.
(4)
The blower motor starts when the
selector switch is placed in the VENTILATE position.
(5)
In the "COOL" position, the blower
motor is in operation and the compressor motor
contactor is energized through the normally closed
contacts of the circuit breaker and the compressor
overload protector. After the blower motor and
compressor have started, the flow with- in the refrigerant
system
is
controlled
by
the
temperature
control
thermostat. Sensing a rise in the air temperature above
the set point, the temperature control thermostat closes,
positioning the valves for cooling service. Sensing a fail
in the air temperature below the set point, the contacts
of the temperature control thermostat open, positioning
the valves for bypass service.
b.
Compressor Operation. The compressor
delivers refrigerant gas to the condenser at the correct
pressure
and
temperature
required
for
con
5-3
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