Cooling Components; Compressors; Crankcase Heaters; High Pressure Switches - Lennox LGH Series Unit Information

B-Cooling Components
Standard and high efficiency units use independent cooling
circuits consisting of separate compressors, condenser coils
and evaporator coils. See figure 12 or 13. Ultra high efficien­
cy units use a common cooling circuit consisting of two
compressors in parallel, two condenser coils in parallel,
and one evaporator coil. See figure 14. On standard and
high efficiency units, two draw-through type condenser fans
are used. On ultra high efficiency units, three draw-through
type condenser fans are used. Standard and high efficiency
units are equipped with belt‐drive blowers which draw air
across the evaporator during unit operation. Ultra high effi­
ciency units are equipped with either a belt-drive blower or a
drive drive blower which draws air across the evaporator
during unit operation.
On standard and high efficiency units, the evaporators are
slab type and are stacked. Each evaporator uses a thermo­
static expansion valve as the primary expansion device. Ul­
tra high efficiency units are equipped with a single slab style
evaporator. The evaporator uses two thermostatic expan­
sions valves. Evaporators are equipped with enhanced fins
and rifled tubing.
In all units, each compressor is protected by a crankcase
heater, high pressure switch and low pressure switch. Addi­
tional protection is provided by low ambient switches and
freezestats. Ultra high efficiency units are also equipped
with a suction line pressure transducer and compressor
sump thermistors (temperature sensors) for added com­
pressor reliability.
Cooling may be supplemented by a factory‐ or field‐in­
stalled economizer.
1-Compressors B1, B2
Standard and high efficiency units are equipped with two
scroll compressors and two independent cooling circuits.
Ultra efficiency units are equipped with two scroll com­
pressors and one common cooling circuit. Compressor
capacity may vary from stage to stage. In all cases, the ca­
pacity of each compressor is added to reach the total ca­
pacity of the unit. See "SPECIFICATIONS" and "ELEC­
TRICAL DATA" (table of contents) or compressor
nameplate for compressor specifications.
WARNING
Electrical shock hazard.
grounded. Do not operate without protective cover over
terminals. Disconnect power before removing protec­
tive cover. Discharge capacitors before servicing unit.
Failure to follow these precautions could cause electri­
cal shock resulting in injury or death.
Each compressor is energized by a corresponding com­
pressor contactor.
Compressor must be
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NOTE-Refer to the wiring diagram section for specific unit
operation.
If Interlink compressor replacement is necessary, call
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-Crankcase Heaters HR1, HR2
All LGH units use insertion type heaters. Heater HR1 is in­
stalled around compressor B1 and heater HR2 is installed
around compressor B2. Crankcase heater wattage varies
by compressor size.
3-High Pressure Switches S4, S7
The high pressure switch is an auto‐reset SPST N.C.
switch which opens on a pressure rise. All units are
equipped with this switch. On fin/tube outdoor coils, the
switch is located in the compressor discharge line. On all-
aluminum outdoor coils, the switch is located on the liquid
line in the blower section. Switches are wired in series with
the compressor contactor coil.
On standard and high efficiency units, S4 (first circuit) and
S7 (second circuit) are wired in series with the respective
compressor contactor coils. On ultra high efficiency units,
only S4 is used. S4 is located on the common compressor
discharge line and is wired to both compressor contactors
via the A55 Unit Controller.
All-Aluminum Coil Units -
When discharge pressure rises to 610 ± 15 psig (4206 ±
103 kPa) (indicating a problem in the system) the switch
opens and the respective compressor is de-energized
(the economizer can continue to operate). When dis­
charge pressure drops to 475 ± 15 psig (3275 ± 103 kPa)
the pressure switch will close.
Fin/Tube Coil Units -
On standard and high efficiency units, when discharge
pressure rises to 640 ± 10 psig (4413 ± 69 kPa) (indicat­
ing a problem in the system) the switch opens and the re­
spective compressor is de-energized (the economizer
can continue to operate). When discharge pressure
drops to 475 ± 20 psig (3275 ± 138 kPa) the pressure
switch will close.
On ultra high efficiency units, BOTH compressors are de-
energized or energized at the pressures listed in the previ­
ous paragraph.
The A55 Unit Controller has a three-strike counter before
locking out. This means the control allows three high
pressure trips per one thermostat demand. The control
can be reset by breaking and remaking the thermostat
demand or manually resetting the control.