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 normally open and closes when the mode selector
LOW HEAT and HIGH HEAT. For a description
switch is moved to the COOL mode. When it
of each position of the switch, refer to table 2-1.
closes power is provided to the compressor power
b. Testing. Remove the control panel from the
circuit. The heater control relay K2 is identical to
air conditioner (para 4-36c). Tag and disconnect
t h e compressor relay. This relay controls the power
t h e leads to the selector switch. Refer to the switch
to one of the two banks of three heating elements in
position table of figure 1-7 for the contact
the air conditioner.
relationship in each mode position. Use an ohm-
b. Testing. Remove the junction box from the
meter and measure the resistance between the
air conditioner (para 4 - 3 6 b ) . Tag and disconnect
related contacts at each switch setting. Contacts
the leads to the relay. Use an ohmmeter and
a c r o s s terminals in the closed positions should read
measure the resistance between contacts A1 to A2,
zero ohms and in the open positions should read
B 1 to B2 and C1 to C2. An open circuit should be
infinite ohms.
i n d i c a t e d . Next apply 28 volts DC to coil terminals
c. Removal. Loosen the set screw in the knob
X1 and X2. A closed circuit should be indicated
with an 5/64 Hexagon Head wrench and remove
from A1 to A2, B1 to B2 and C1 to C2.
the knob. Remove the nut, washer and lockwasher
c. Remoual. Remove the four nuts and screws
which secure the switch to the control panel and
w h i c h secure the contactor to the back panel of the
rem ove the switch.
junction box.
d. Installation. Installation shall be in the
d. Installation. Installation shall be in the
reverse order of removal.
reverse order of removal.
4-42. Fuses
a. Function. `This is an adjustable, single pole,
a . F u n c t i o n . There are two fuses included in the
double throw device that directs current to
junction box. They serve to protect the control
associated elements of the heating and cooling
c i r c u i t from damage due to short circuits. Fuse F1
c i r c u i t s of the air conditioner. It has an adjustable
protects the prim ary side of the transformer and
r a n g e from 40 to 70 degrees F. with a 1.75 degrees
fuse F2 protects the low voltage control circuit.
F . differential at any given setting. When the mode
h. Testing. Remove the junction box from the
selector switch is positioned on the cooling mode
air conditioner (para 4-36b). Remove the fuses
t h e thermostat controls the action of the liquid line
from the fuseholders located inside the left end
s o l e n o i d valve to reduce the cooling capacity when
panel of the junction box. Measure the resistance
the return air temperature is below the setting of
across the fuse with an ohmmeter. The resistance
the thermostat. When the mode selector switch is
should be approximately zero ohms.
positioned on either of the heating modes the
c. Installation. R e p l a c e
the
fuses
in t h e i r
thermostat controls the opening of the heater
r e s p e c t i v e fuseholders. Make sure that the fuses are
c o n t r o l relay. When the temperature rises above the
securely seated in the holder clips.
s e t t i n g of the thermostat it opens to open the relay
a n d break the power circuit to one bank of heaters.
b. Testing. Remove the control panel from the
air conditioner (para 4-36c). Tag and disconnect
(RFI) suppression capacitor C3 is included in the
t h e leads to the thermostat. With the thermostat set
control circuitry to reduce RFI noise generated by
below room temperature measure for continuity
t h e rectifier.
with an ohmmeter from terminal "R" to terminal
b. Removal and Testing. Remove the junction
"BL". Resistance should be zero ohms. Move the
box from the air conditioner (para 4-36b). T a g
setting to a position above room temperature. The
a n d disconnect the leads to the output terminals X1
resistance across terminals "R" and "BL" should
and X2 of the transformer and remove the
be infinity indicating an open circuit.
capacitor from across these terminals. Apply 60
c. Removal. Remove the four nuts and screws
Hertz test voltage not exceeding 200 volts across
w h i c h secure the thermostat to the back plate of the
the capacitor terminals. Measure the voltage across
control panel.
the capacitor and the amperage draw. The
d. Installation. Installation shall be in the
capacitance should be 1 microfarad 10 per cent
reverse order of removal.
when calculated by the following formula: 2650 X
Amperage divided by voltage.
c. Installation. Installation
shall
be
in t h e
a. F u n c t i o n . The fan speed switch is supplied to
reverse order of removal.
s e l e c t operation of the fan motor on either. low or
high speed.
b. Testing. Remove the control panel from the
a . Function. The mode selector switch is used to
air conditioner (para 4-36c). Tag and disconnect
s e l e c t the mode of operation for the air conditioner.
t h e leads to the fan speed switch. Place the switch
Modes available are OFF, VENTILATE, COOL,
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