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I−UNIT COMPONENTS
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
CAUTION
ELECTROSTATIC DISCHARGE CAN AFFECT
ELECTRONIC COMPONENTS. TAKE PRECAU-
TIONS DURING UNIT INSTALLATION AND SER-
VICE TO PROTECT THE UNIT’S ELECTRONIC
CONTROLS. PRECAUTIONS WILL HELP TO
AVOID CONTROL EXPOSURE TO ELECTRO-
STATIC DISCHARGE BY PUTTING THE UNIT,
THE CONTROL AND THE TECHNICIAN AT THE
SAME ELECTROSTATIC POTENTIAL.
NEUTRALIZE ELECTROSTATIC CHARGE BY
TOUCHING HAND AND ALL TOOLS ON AN UN-
PAINTED UNIT SURFACE BEFORE PERFORM-
ING ANY SERVICE PROCEDURE.
SCA/SCB unit components are shown in figures 1 and 2. All
L1, L2, and L3 wiring is color coded; L1 is red, L2 is yellow,
and L3 is blue.
A−Control Box Components
SCA/SCB control box components are shown in figure 3
and 4. The control box is located in the upper left portion of
the compressor compartment.
1−Circuit Breaker CB10
All units are equipped with circuit breaker CB10. Circuit
breaker CB10 is a toggle switch which can be used by the
service technician to disconnect power to the unit.
2−Control Transformer T1 (all units)
All use a single line voltage to 24VAC transformer
mounted in the control box. Transformer supplies power
to control circuits in the unit. The transformer is rated at
70VA and is protected by a 3.5 amp circuit breaker
(CB8). The 208/230 (Y) voltage transformers use two
primary voltage taps
as shown in figure 5,
while 460 (G) and 575
(J) voltage transform-
ers use a single prima-
ry voltage tap.
3−Contactor Transformer T18
(SCA240/SCB288 units)
T18 is a single line voltage to 24VAC transformer used in
all 10, 20 and 24 ton series units. Transformer T18 is
protected by a 3.5 amp circuit breaker (CB18). T18 is iden-
tical to transformer T1. The transformer supplies 24VAC
power to the contactors.
4−Terminal Strips TB1, TB13, TB34 (all units),
and TB35 (SCA240/SCB288 units)
TB1 terminal strip distributes 24V power and common from
the thermostat to the control box components. TB13 termi-
nal strip distributes line voltage power to the line voltage
items in the unit. TB34 terminal strip distributes 24V pow-
er from T1 to the control box components. TB35 terminal
strip distributes 24V power from T18 to the contactors in
the control box.
5−Outdoor Fan Motor Fuse Block & Fuses F10
(SCA240/SCB288 units)
Three line voltage fuses F10 provide overcurrent protec-
tion to all condenser fans in all SCA240/SCB288 units.
The fuses are rated at 30A in 208/230V units and 15A in all
others.
6−Power Exhaust Fan Fuse Block F6
(SCA240/SCB288)
Two line voltage fuses F6 provide overcurrent protection
to all condenser fans in all SCA240/SCB288 units. The
fuses are rated at 15A.
7−Outdoor Fan Capacitors C1 & C2 (all units),
C18, C19, C20 & C21 (SCA240/SCB288)
Fan capacitors C1, C2, C18, C19 are 370V / 10 MFD capaci-
tors used to assist in the start up of condenser fans B4, B5,
B21, B22, B23 and B24 respectively.
8−Compressor Contactor K1 & K2 (all units),
K14 and K146 (SCA 240/SCB288 units)
All compressor contactors are three-pole-double-break
contactors with 24VAC coils. In all the SCA120 units, K1
(energized by A55) and K2 (energized by A57) energize
compressors B1 and B2 in response to thermostat de-
mand. In the SCA240/SCB288 units, K1 (energized by
A55), K2 (energized by A57), K14 and K16 (energized
by A59), energize compressors B1, B2, B13 and B20 in
response to first or second stage cool demand.
FIGURE 5
BLUE YELLOW
ORANGE
RED
BLACK
230 VOLTS
208 VOLTS
PRIMARY
SECONDARY
208/230V TRANSFORMER
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