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B-Cooling Components
LDT units use independent cooling circuits consisting of
separate compressors, outdoor coils and indoor coil (with
with two or three draw-through type condenser fans. and
directdrive blowers. The blower draws air across the in-
door coil during unit operation.
-
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
all units, each compressor is protected by a crankcase
heater, high pressure switch and low pressure switch. Ad-
ditional 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 “SPECI-
WARNING
Electrical shock hazard. Compressor must be
grounded. Do not operate without protective
coverover terminals. Disconnect power before
removing protective cover. Discharge capacitors
before servicing 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-
operation.
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
unloaded. Protector will reset when low pressure
in system rises above 40 psig. DO NOT REPLACE
COMPRESSOR.
2-Freezestats S49 and S50
Each unit is equipped with a low temperature switch
the corresponding indoor coils.
Each freezestat is a SPST N.C. auto-reset switch which
+ +
+ +
temperature rise. To prevent coil icing, freezestats open
during compressor operation to temporarily disable the
melt any accumulated frost.
If the freezestats are tripping frequently due to coil icing,
unit back in operation. Make sure to eliminate conditions
which might promote indoor coil ice buildup.
3-High Pressure Switches S4 and S7
The high pressure switches is a manual reset SPST N.C.
switch which opens on a pressure rise. The switch is locat-
ed in the compressor discharge line and is wired in series
with the compressor contactor coil.
with the respective compressor contactor coils. When dis-
the respective compressor is de-energized (the econo-
4-Low Pressure Switches S87, S88
The low pressure switch is an auto-reset SPST N.O.
a pressure drop. All units are equipped with this switch.
The switch is located in the compressor suction line.
-
sure switches by shunting the switches during start up un-
til pressure is stabilized. After the shunt period, the control
before the compressor is locked out. The control is reset
by breaking and remaking the thermostat demand or man-
ually resetting the control.
+
when pressure in the suction line rises to 40 +
to many causes such as refrigerant being added.
+ 10 psig (3102 +
the appropriate switch opens. The switches automatically
reset when pressure in the suction line drops to 300 + 20
psig (2068 +
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