Lennox LCH060H4E

Page 34
B-Cooling Components
All units use independent cooling circuits consisting of sepa
rate compressor, condenser coil and evaporator coil. See
figure 6. One draw-through type condenser fan is used in
LCH036-074 units. Units are equipped with belt‐drive or di
rect drive blowers which draw air across the evaporator dur
ing unit operation.
Cooling may be supplemented by a factory‐ or field‐
installed economizer. The evaporator coil is slab type and
uses a thermostatic expansion valve as the primary refriger
ant metering device. Each evaporator is also equipped with
enhanced fins and rifled tubing. In all units each compressor is
protected by a freezestat (S49) on the evaporator coil, a high
pressure switch (S4) on the discharge line, and a low pres
sure switch (S87) on the suction line. See figure 6. A low am
bient switch (S11) is standard.
1-Compressor B1
All LCH036, 048, 060 and 074 units use one two-stage scroll
compressor. LCH072 units use one single-stage scroll com
pressor. 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-Freezestat S49
Each unit is equipped with a low temperature switch (free
zestat) located on a return bend of each evaporator coil.
The freezestat is wired to the A55 Unit Controller. The
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, freezestats open during com
pressor operation to temporarily disable the respective
compressor until the coil temperature rises.
If the freezestats are tripping frequently due to coil icing,
check the airflow / filters , economizer position and unit
charge before allowing unit back in operation. Make
sure to eliminate conditions which might promote evap
orator ice buildup.
3-High Pressure Switch S4
The high pressure switch is a auto-reset SPST N.C. switch
which opens on a pressure rise.
S4 is located in the compressor discharge line and wired to the
A55 Unit Controller.
When discharge pressure rises to 640 ± 10 psig (4412 ±
69 kPa) (indicating a problem in the system) the switch
opens and the respective compressor is de-energized
(the economizer can continue to operate). The switch au
tomatically resets at 475 +
10 psig.
4-Low Ambient Switch S11
The low ambient switch is used to maintain cooling op
eration during low ambient temperatures. The switch
opens to de-energize the outdoor fan (via A55) while
mechanical cooling continues to operate. The reduced
heat transfer across the outdoor coil results in higher re
frigerant temperatures and prevents indoor coil icing.
The low ambient switch is an auto‐reset SPST N.O. pres
sure switch and is located in the liquid line prior to the in
door coil section. The switch is wired to the A55 Unit
Controller which uses the S11 input to control the out
door fan when outdoor temperatures drop below 62°F.
S11 opens when the liquid pressure drops below 240 ±
10 psig (1655 ± 69 kPa). S11 closes when the liquid pres
sure rises to 450 ± 10 psig (3102 ± 69 kPa) psig. The S11
switch will continue to cycle the outdoor fan until the out
door temperature rises to 65°F.
Units Equipped With Direct Drive Blowers -
When the liquid pressure rises to 450 psig, the outdoor fan
is energized at extra low RPM. This reduces the number of
outdoor fan on/off cycles and refrigerant pressure fluctua
tions. The outdoor fan will continue to operate at extra low
RPM until the outdoor temperature rises to 65°F.
5-Low Pressure Switch S87
The compressor circuit is protected by a low pressure
switch located on the suction line. Switch opens at 40 psig +
5 psig (276 + 34 kPa) and automatically resets at 90 psig + 5
psig (621 kPa +
kPa).
6-Crankcase Thermostat S40
Switch opens when discharge line temperature reaches
94_F+
5 (34_C+3) and closes when temperature falls below
74_F+
5 (23_C+3). Prevents crankcase heater operation in
warm weather.