Lennox ALLIED Commercial TCA180S2B Standard Manual page 24

B−Cooling Components
All units use independent cooling circuits consisting of sepa-
rate compressors, condenser coils and evaporator coils.
See figures 7 and 8. Four draw−through type condenser fans
are used in TCA180/300 units. All units are equipped with
belt-drive blowers which draw air across the evaporator dur-
ing unit operation.
Cooling may be supplemented by an optional field-
installed economizer. The evaporators are slab type
and are stacked. Each evaporator uses a thermostatic ex-
pansion valve as the primary expansion device. Each evap-
orator is also equipped with enhanced fins and rifled tubing. In
all units each compressor is protected by a freezestat (on
each evaporator). Optional field installed low ambient
switches and optional field installed high pressure switches
are availabe for additional compresor protection.
1−Compressors B1, B2 & B13 (all units)
B20 (TCA210H/240H/300S only)
All TCA180/300 units use scroll compressors. TCA180,
210S and 240S units use 3 compressors and TCA210H,
240H and 300S use four compressors. All compressors are
equipped with independent cooling circuits. Compressor ca-
pacity may vary from stage to stage. In all cases, the capac-
ity of each compressor is added to reach the total capacity of
the unit. See SPECIFICATIONS" and ELECTRICAL
DATA" (table of contents) or compressor nameplate for
compressor specifications.
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−High Pressure Switches (optional)
S4, S7 & S28 (all units)
S96 (TCA210H, 240H, 300S only)
The high pressure switches is a manual reset SPST N.C.
switch which opens on a pressure rise.
S4 (first circuit), S7 (second circuit), S28 (third circuit), and S96
(fourth circuit) are wired in series with the respective compres-
sor contactor coils.
When discharge pressure rises to 450 ± 10 psig (3103 ±
69 kPa) (indicating a problem in the system) the switch
opens and the respective compressor is de−energized
(the economizer can continue to operate).
3−Low Ambient Switches (optional) S11, S84
& S85 (all units)
S94 (210H, 240H, 300S only)
The low ambient switch is an optional field installed auto-
reset N.O. pressure switch which allows for mechanical
cooling operation at low outdoor temperatures. The
switch is located in each liquid line prior to the indoor coil
in the blower compartment.
In three compressor units, S11 (compressor 1) is wired in se-
ries with outdoor fan relay K10 coil. S84 (compressor 2) and
S85 (compressor 3) are wired in parallel with the outdoor fan
relay K68 coil.
In four compressor units, S11 (compressor 1) and S84 (com-
pressor 2) are wired in parallel with outdoor fan relay K10. S85
(compressor 3) and S94 (compressor 4) are wired parallel with
outdoor fan relay K68.
When liquid pressure rises to 275 ± 10 psig (1896 ± 69
kPa), that switch closes. When discharge pressure in one
refrigerant circuit drops to 150 ± 10 psig (1034 ± 69 kPa),
that switch opens. The pair of condenser fans are ener-
gized when one switch in parallel with the outdoor fan relay
closes. To de−energize the outdoor fan relay, both switches
in parallel must open before the fans are de−energized.
This intermittent fan operation results in higher evaporating
temperature allowing the system to operate without icing
the evaporator coil and losing capacity.
4−Filter Drier (all units)
TCA units have a filter drier located in the liquid line of each
refrigerant circuit at the exit of each condenser coil. The dri-
er removes contaminants and moisture from the system.
5−Freezestats S49, S50 & S53 (all units)
S59 (TCA210H/240H/300S only)
Each unit is equipped with a low temperature switch (freezes-
tat) located on a return bend of each evaporator coil. S49
(first circuit), S50 (second circuit) and S53 (third circuit)
are located on the corresponding evaporator coils. On
the 210H, 240H and 300S models, S95 is located on the
fourth circuit.
Each freezestat is wired in series with the corresponding
compressor contactor. Each freezestat is a SPST N.C. auto−
reset switch which opens at 29°F + 3°F (-1.7°C + 1.7°C) on a
temperature drop and closes at 58°F + 4°F (14.4°C +
2.2°C) on a temperature rise. To prevent coil icing, free-
zestats open during compressor operation to temporari-
ly disable the respective compressor until the coil tem-
perature rises.
6−Condenser Fans B4, B5, B21 & B22
See SPECIFICATIONS tables at the front of this manual
for specifications of condenser fans used in all units. All
condenser fans used have single−phase motors. The fan
assembly may be removed for servicing and cleaning.
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