Page 18
B-Cooling Components
LHT units use independent cooling circuits consisting of
separate compressors, outdoor coils and indoor coil (with 2
separate stages). See figure 4. Units are equipped with two
or three draw-through type condenser fans. and direct-
drive blowers. The blower draws air across the indoor coil
during unit operation.
Cooling may be supplemented by a factory‐or-field‐in
stalled economizer. The indoor coils are slab type and are
stacked. Each indoor coil uses a thermostatic expansion
valve as the primary expansion device. Each indoor coil 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 pressure switch. Additional
protection is provided by by thermistors for low ambient
control and freezing prevention.
1-Compressors B1 and B2
Units use two scroll compressors and two independent
cooling circuits. Compressor 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 “SPECIFI
CATIONS” 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.
IMPORTANT
Some scroll compressors have an internal vacuum
protector that will unload scrolls when suction pres
sure goes below 20 psig. A hissing sound will be
heard when the compressor is running unloaded.
Protector will reset when low pressure in system
rises above 40 psig. DO NOT REPLACE COMPRES
SOR.
2-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.
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 discharge
pressure drops to 475 ± 15 psig (3275 ± 103 kPa) the pres
sure switch will close.
The A55 Unit Controller has a three-strike counter before
locking out. This means the control allows three high pres
sure trips per one thermostat demand. The control can be
reset by breaking and remaking the thermostat demand or
manually resetting the control.
To Next Page
Loading...
Need help?
General
