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CHAPTER 6
REPAIR INSTRUCTIONS
6-1. General
The air conditioner, after it is started, is auto-
matic in operation. The relationship of the auto-
matic components, controls, and instruments, is
explained in the operation analysis for mainte-
nance of the air conditioner (para 6-2). A wiring
diagram (fig. 1-4) and refrigerant flow diagram
(fig. 6-1 ) are included to assist in the mainte-
nance of the electrical components, wiring har-
ness, wire leads, and refrigerant components.
Warning: Disconnect the air conditioner from
the power source before performing any main-
tenance on the components of the unit.
6-2. Analysis of Operation
a. General. The type and degree of air condi-
tioning provided by the unit is controlled by a
five-position rotary selector switch and a thermo-
stat.
(1) Placing the rotary selector switch in the
HI-HEAT position actuates the blower motor and
supplies electrical power to all six electric heat-
ers. The temperature of the electric heaters is reg-
ulated by the thermostat. If the air temperature
falls below the set point of the thermostat, the
control contacts close, energizing the heater relay
( K2) which supplies power to the heaters.
(2) Moving the selector switch to the LO-
HEAT position presents the same control se-
quence but reduces the heating capacity of the
unit by supplying power to only three electric
heaters. A high temperature cutout switch pro-
tects against high temperature in the event of
fan motor malfunction.
(3) The blower motor starts when the selec-
tor switch is placed in the VENTILATE position.
(4) The pressure equalizer solenoid valve
closes at the time the rotary selector switch ( S1 )
is positioned to COOL. It remains energized and
closed as long as the rotary selector switch re-
mains in the COOL position.
(5) In the COOL position, the blower motor
is in operation and the compressor motor contac-
tor is energized, after a thirty-second time delay,
through the contacts of the thermostat. The ener-
gized contactor supplies power to the compressor
through the closed contacts of the circuit
breaker. After the blower motor and compressor
have started, the flow within the refrigerant cir-
cuit is - controlled by the thermostat. Sensing a
rise in the air temperature above the set point,
the thermostat opens its contacts, deenergizing the
compressor bypass solenoid valve (13, fig. 6-1 ).
This positions the valve for cooling service. Sens-
ing a fall in the air temperature below the set
point, the contacts of the thermostat close, ener-
gizing the valve (13). This positions the valve for
bypass service.
b. Cooling Cycle of Operation. The blower
motor and compressor run continuously, whether
the thermostat is calling for cooling or not, when
the unit is adjusted to operate on the cooling
cycle of operation. This feature provides a con-
stant electrical load thus preventing voltage fluc-
tuations within the system.
c. Bypass Cycle of Operation. When the condi-
tioned air temperature falls below the thermostat
setting, the circuit which controls the solenoid
valve (13) is energized, causing:
(1) The compressor bypass solenoid valve
(13) to close, stopping the flow of refrigerant to
the evaporator coil, thus stopping the cooling
function completely.
(2) The system then goes into bypassing a
major part of the compressed refrigerant vapor
directly back to the suction side of the compres-
sor.
(3) The bypass expansion valve will then
modulate a small amount of liquid refrigerant
into the suction tubing.
(4) To prevent f rest from forming on the
evaporator, a back pressure regulating valve is
provided to prevent the suction pressure from de-
creasing to a pressure which corresponds to a
temperature of less than 32° F.
d. Heating Operation. Placing the selector
switch in the LO-HEAT position actuates half of
the evaporator heaters mounted in the condi-
tioned air stream, directly behind the evaporator
coil. When the selector switch is placed in the
6-1
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