Lennox KGA Series Service Literature page 17

B-Cooling Components
All units use independent cooling circuits consisting of sepa­
rate compressors, condenser coils and evaporator coils.
See figure 6. Two draw-through-type condenser fans are
used in KGA092/150 units. All units are equipped with belt‐
drive blowers which draw air across the evaporator during
unit operation.
Cooling may be supplemented by a factory‐ or field‐
installed economizer. The evaporators are slab-type and
are stacked. Each evaporator uses a thermostatic expan­
sion valve as the primary refrigerant metering device. Each
evaporator is also equipped with enhanced fins and rifled
tubing.
In all units each compressor is protected by S49 and S50
freezestats and S4 and S7 high pressure switches (on each
evaporator). Low ambient switches (S11 and S84) are avail­
able as an option for additional compressor protection. On
150 units, each compressor is protected by a crankcase
heater.
1-Compressors B1 and B2
All KGA092/150 units use two scroll compressors. Com­
pressor capacity may vary from stage to stage. In all cases,
the capacity of each compressor is added to reach the total
capacity of the unit. See "SPECIFICATIONS" and "ELEC­
TRICAL 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.
If Interlink compressor replacement is necessary, call
1-800-4-LENNOX (1-800-453-6669).
IMPORTANT
Some scroll compressors have an internal vacuum
protector that will unload scrolls when suction
pressure goes below 20 psig. A hissing sound will
be heard when the compressor is running un­
loaded. Protector will reset when low pressure in
system rises above 40 psig. DO NOT REPLACE
COMPRESSOR.
2-Thermal Protectors S5, S8
Some compressors have thermal protectors located on top
of the compressor. The protectors open at 248°F + 9°F
(120°C + 5°C) and close at 169°F + 18°F (76°C + 10°C).
3-Freezestats S49 and S50
Each unit is equipped with a low temperature switch (freezes­
tat) located on a return bend of each evaporator coil. S49
(first circuit) and S50 (second circuit) are located on the
corresponding evaporator coils.
Freezestats are wired in series with compressor contactors.
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 tempera­
ture rise. To prevent coil icing, freezestats open during
compressor operation to temporarily disable the re­
spective 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 evaporator
ice buildup.
4-High Pressure Switches S4 and S7
The high pressure switch is a manual reset SPST N.C. switch
which opens on a pressure rise.
S4 (first circuit) and S7 (second circuit) are located in the
compressor discharge line and are wired in series with the
respective compressor contactor coils.
When discharge pressure rises to 640 ± 10 psig (4413 ±
69 kPa) (indicating a problem in the system), the switch
opens and the respective compressor is de-energized
(the economizer can continue to operate).
5-Low Ambient Switches S11 & S84
(optional)
The low ambient switch is an auto‐reset SPST N.O. pres­
sure switch which allows for mechanical cooling operation
at low outdoor temperatures. In all models, a switch is lo­
cated in each liquid line prior to the indoor coil section.
In the KGA092/150, S11 and S84 are wired in parallel with
outdoor fan relay K10.
When liquid pressure rises to 450 ± 10 psig (3102 ± 69
kPa), the switch closes and the condenser fans are ener­
gized. When liquid pressure in both refrigerant circuits
drops to 240 ± 10 psig (1655 ± 69 kPa), the switches open
and the condenser fans are de-energized. This intermittent
fan operation results in higher evaporating temperature al­
lowing the system to operate without icing the evaporator
coil and losing capacity.
6-Crankcase Heaters HR1, HR2
150S units use insertion-type heaters. Heater HR1 is
installed around compressor B1 and heater HR2 is
installed around compressor B2. Crankcase heater watt­
age varies by compressor manufacturer.
Page 17