Thermo King 914 724, Manual

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Unit Description (Rev. 1/99)
8
the adjacent cavity in the compressor head. When the dis-
charge gas is cooled to 200 ± 5 F (93 ± 3 C), the high tem-
perature switch opens, the liquid injection solenoid valve
closes and refrigerant no longer flows through the liquid
injection system.
Oil Separator
An oil separator is a standard feature. It separates compres-
sor oil from refrigerant vapor and returns the oil to the com-
pressor through the oil fill hole by using a special adapter.
The oil separator helps provide positive oil return at high
compressor speeds and low operating temperatures. This
feature enhances compressor lubrication and extends com-
pressor life.
CBci MAX Features
The CBci MAX is functionally the same as CBci units, but
it uses R-404A refrigerant. This unit has a redesigned evap-
orator in order to operate more efficiently with R-404A
refrigerant. All other operating features are the same as
CBci units.
UNIT OPERATION
These units shift between cool, null, and heat (optional) to
maintain the box temperature at the thermostat setpoint. The
operating modes are: cool, null, heat (optional), and defrost.
The thermostat controls the operation of the unit by energiz-
ing and de-energizing the cool relay and the heat relay.
When the cool relay is energized, it closes contacts that
energize the fan relay and the compressor clutch (or the
compressor motor contactor on Model 20 units during elec-
tric standby operation).
When the heat relay is energized, it closes contacts that
energize the fan relay.
When the fan relay is energized, it closes contacts that ener-
gize the condenser and evaporator fans. The condenser fan
is also controlled by the condenser fan pressure switch. This
normally open switch monitors the compressor discharge
pressure. When the discharge pressure rises to 180 ± 10 psi
(1241 ± 69 kPa), the switch closes and energizes the con-
denser fan. When the discharge pressure drops to 130 ± 10
psi (896 ± 69 kPa), the switch opens and de-energizes the
condenser fan.
Cool
The thermostat energizes the cool relay at box temperatures
above setpoint when the temperature is dropping. The ther-
mostat energizes the cool relay at box temperatures more
than 2 ± 1 F (1 ± 0.5 C) above setpoint when the tempera-
ture is rising. The cool relay energizes the fan relay and the
compressor clutch (or motor contactor). The fans and the
compressor run and the unit cools.
Null
The thermostat de-energizes the cool relay and the heat
relay at box temperatures between setpoint and 2 ± 1 F (1 ±
0.5 C) below setpoint when the temperature is dropping.
The thermostat de-energizes the cool relay and the heat
relay at box temperatures between setpoint and 2 ± 1 F (1 ±
0.5 C) above setpoint when the temperature is rising. When
the cool relay and the heat relay are both de-energized, the
unit does not operate unless it is in defrost.
Heat (Optional)
NOTE: Heat lockout occurs at setpoints of 15 F (-9.5 C)
and lower. Heat lockout disables Heat and replaces Heat
with Null.
The thermostat energizes the heat relay at box temperatures
more than 2 ± 1 F (1 ± 0.5 C) below setpoint when the tem-
perature is dropping. The thermostat energizes the heat
relay at box temperatures below setpoint when the tempera-
ture is rising. The heat relay energizes the fan relay, but the
compressor clutch (or motor contactor) is not energized.
Therefore, the evaporator fans run but the condenser fan