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TM 5-4120-270-15
CHAPTER 6
SPECIFIC REPAIR INSTRUCTIONS
Section I. ELECTRICAL SYSTEM
6-1. General
This section contains those items which are considered
part of major components or auxiliaries of the air
conditioner electrical system. They consist of control
circuit components, leads, heating elements, relays and
electric motors.
6-2. Selector Switch
a. General. The selector switch is a manually
operated, five-position rotary switch which is used to turn
on the "COOL", "HEAT" and "VENTILATE" modes and to
turn off the air conditioner.
b. Removal. Refer to figure 6-1 and remove the
selector switch from the control panel.
c. Disassembly. Disconnect electrical leads from
selector switch. Do not disassemble further.
d. Testing. Using a multimeter set on OHMS, refer to
figure 62 and test for continuity or open circuit as
indicated on the chart. Replace the selector switch if it
fails to operate as specified.
e. Reassembly. Connect electrical leads to selector
switch.
f. Installation. Refer to figure 6-1 and install the
selector switch in the control panel.
6-3. Temperature Control Thermostat
a. General. The temperature control thermostat is a
temperature sensing manually set single pole double-
throw switch which automatically controls both heating
and cooling cycles to maintain any selected conditioned
area temperature between +40’F and +900F.
b. Removal. Refer to figure 6-1 and remove the
temperature control thermostat from the control panel.
c. Disassembly. Disconnect electrical leads from
temperature control thermostat. Do not disassemble
further.
d. Testing.
(1) Rotate shaft so flat faces away from terminal.
Using a multimeter set on OHMS, refer to figure 6-8 and
test for continuity between each of the control terminals
and the common terminal. It will be necessary to rotate
the
shaft
clockwise
("warmer"
direction)
or
counterclockwise ("cooler" direction) to open and close
each set of contacts. Replace temperature control
thermostat if contacts do not operate as indicated.
(2) The temperature control thermostat should
maintain conditioned area temperature within 2° F 1°F of
the temperature selected. Replace temperature control
thermostat if operating differential is larger than
specified.
e. Reassembly. Connect electrical leads to
temperature control thermostat.
f. Installation. Refer to figure 6-1 and install
temperature control thermostat in the control panel.
6-4. Circuit Breaker
a. General. The circuit breaker is a manually reset,
double-pole double-throw switch which automatically
protects the compressor motor from continuous
overcurrent and short circuits. An electrically isolated
single-pole double-throw switch protects the control
circuits.
b. Removal. Refer to figure 6-4 and remove the
circuit breaker from the junction box.
c. Testing.
(1) Refer to figure 6-5. With circuit breaker closed,
there should be continuity between terminals 1 and 2, 8
and 5, 6 and 7.
(2) With circuit breaker open there should be no
continuity between terminals 1 and 2, 8 and 5, 6 and 7.
Replace circuit breaker if operation is not as indicated.
d. Installation. Refer to figure 64 and install circuit
breaker in the junction box.
6-5. Magnetic Contactors
a. General. The magnetic contactors are remote
controlled three-pole, single-throw switches which are
used to connect the air conditioner electric motors and
heaters across the line. The control coils operate on
6-1
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