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B-Cooling Components
LGA/LCA units use independent cooling circuits consisting
of separate compressor, condenser coil and evaporator coil.
See figure 7. Units are equipped with a draw-through type
condenser fan. All units are equipped with either belt-drive
or direct drive blowers which draw air across the evaporator
during unit operation.
Cooling may be supplemented by a factory- or field-
installed economizer. The evaporator is slab type and
uses a thermostatic expansion valve as the primary expan-
sion device. Each evaporator is also equipped with enhanced
fins and rifled tubing. In all units each compressor is protected
by a crankcase heater, high pressure switch and low pres-
sure switch. Additional protection is provided by the low am-
bient switch and freezestat.
1-Compressors B1 (all units )
All LGA/LCA 3 through 5 ton (10.5 to 17.6 kW) standard effi-
ciency units use one reciprocating type compressor. All LGA/
LCA 6 ton (21kW) standard efficiency units use one scroll
compressor. All LGA/LCA 3 through 6 ton (10.5 to 21 kW)
high efficiency units use one scroll compressor. Compres-
sors are supplied by various manufacturers. Compressor
electrical specifications vary by manufacturer.
WARNING
Electrical shock hazard. Compressor must be
grounded. Do not operate without protective cover
over terminals. Disconnect power before removing
protective cover. Discharge capacitors before ser-
vicing unit. Failure to follow these precautions could
cause electrical shock resulting in injury or death.
Each compressor is energized by a corresponding com-
pressor contactor.
NOTE-Refer to the wiring diagram section for specific unit
operation.
2-Compressor Run Capacitor (C12)
Single-phase units use single-phase PSC compressor mo-
tors. PSC motors require a run capacitor C12.
The run capacitor is a "dual" capacitor which is shared with the
condenser fan motor. A dual capacitor functions as two capac-
itors in a single can. One side of the dual capacitor is con-
nected to the compressor and the other side of the capacitor is
connected to the condenser fan. Each side of the capacitor
has a different rating.
Capacitor ratings may be different for each motor, but the rat-
ing and repair part number is printed on the capacitor.
3-Crankcase Heaters HR1 (all units)
All LGA/LCA units with scroll compressors use belly-band
type crankcase heaters, while all LGA/LCA units with recip-
rocating compressors use insertion type heaters. Heater
HR1 is used on compressor B1. Crankcase heater wattage
varies by compressor manufacturer.
4-High Pressure Switch S4 (all units)
The high pressure switch is an auto-reset SPST N.C. switch
which opens on a pressure rise. All LGA/LCA units are
equipped with this switch. The switch is located in the com-
pressor discharge line. S4 is wired in series with the compres-
sor contactor coil.
When discharge pressure rises to 450 + 10 psig (3103+
69 kPa) (indicating a problem in the system) the switch
opens and the compressor is de-energized (the econo-
mizer can continue to operate). When discharge pres-
sure drops to 310 + 20 psig (2147 + 138 kPa) the pressure
switch will close.
Main control A55 has a three-strike counter before lock-
ing out. This means the control will allow three high pres-
sure trips per one thermostat demand. The control can
be reset by breaking and remaking the thermostat de-
mand or manually resetting the control.
5-Low Ambient Switches S11 (all units)
The low ambient switch is an auto-reset SPST N.O. pres-
sure switch which allows for mechanical cooling opera-
tion at low outdoor temperatures. All LGA/LCA units are
equipped with this switch. In all models a switch is lo-
cated in each liquid line prior to the indoor coil section.
When liquid pressure rises to 275 + 10 psig (1896 + 69
kPa), the switch closes and the condenser fan is ener-
gized. When discharge pressure in both refrigerant circuits
drop to 140 + 10 psig (965 + 69 kPa), the switch opens and
the condenser fan is de-energized. This intermittent fan op-
eration results in higher evaporating temperature allowing
the system to operate without icing the evaporator coil and
losing capacity.
6-Low Pressure Switches S87 (all units)
The low pressure switch is an auto-reset SPST N.O.
switch (held N.C. by refrigerant pressure) which opens
on a pressure drop. All LGA/LCA units are equipped
with this switch. The switch is located in the compressor
suction line.
S87 is wired directly to the main control module A55.
Page 18
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