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II−PLACEMENT AND INSTALLATION
Make sure the unit is installed in accordance with the
installation instructions and all applicable codes.
III−CHARGING
IMPORTANT−The crankcase heater must be energized for
24 hours before attempting to start compressor. Set thermo-
stat so there is no demand to prevent compressors from
cycling. Apply power to unit.
A−Preliminary Checks
1− Make sure that unit is installed in accordance with the
installation instructions and applicable codes.
2− Inspect all electrical wiring, both field- and factory-
installed, for loose connections. Tighten as required.
3− Check to ensure that refrigerant lines do not rub against
the cabinet or against other refrigerant lines.
4− Check voltage at disconnect switch. Voltage must be
within range listed on nameplate. If not, consult power
company and have voltage condition corrected before
starting unit.
5− Make sure filters are in place before start-up.
B−Start−Up
1− Initiate first and second stage cooling demands ac-
cording to instructions provided with thermostat. Refer
to the Optional Supply Air VFD section on MSAVt
units.
SCA120 Units−
First−stage thermostat demand will energize compres-
sor 1. Second−stage thermostat demand will energize
compressor 2. On units with an economizer, when out-
door air is acceptable, a first−stage demand will ener-
gize the economizer; a second−stage demand will en-
ergize compressor 1.
SCA240/SCB288 Units−
First−stage thermostat demand will energize compres-
sors 1 and 2. Second−stage thermostat demand will
energize compressors 3 and 4. On units with an econo-
mizer, when outdoor air is acceptable, a first−stage de-
mand will energize the economizer; a second−stage
demand will energize compressors 1 and 2.
3− SCA120 units contain two refrigerant circuits and two
stages of cooling. See figure 9.
4− SCA240/SCB288 units contain four refrigerant circuits
or systems. Evaporator and condenser coil refrigerant
circuits 1 and 2 make up stage 1 cooling. Evaporator
and condenser refrigerant circuits 3 and 4 make up
stage 2 cooling. See figure 11.
5− Each refrigerant circuit is separately charged with
R410A refrigerant. See unit rating plate for correct
amount of charge.
6− Refer to Cooling Operation and Adjustment section for
proper method to check refrigerant charge.
C−Three Phase Scroll Compressor
Voltage Phasing
Three phase scroll compressors must be phased se-
quentially to ensure correct compressor and blower rota-
tion and operation. Compressor and blower are wired in
phase at the factory.
1− Observe suction and discharge pressures and blower
rotation on unit start−up.
2− Suction pressure must drop, discharge pressure must
rise, and blower rotation must match rotation marking.
If pressure differential is not observed or blower rotation is
not correct:
3− Disconnect all remote electrical power supplies.
4− Reverse any two wires at the line voltage wiring to unit.
Do not reverse wires at blower contactor.
5− Make sure the connections are tight.
Discharge and suction pressures should operate at their
normal start-up ranges.
D−R410A Refrigerant
Units charged with R410A refrigerant operate at much
higher pressures than R22. The expansion valve and liquid
line drier provided with the unit are approved for use with
R410A. Do not replace them with components designed for
use with R22.
R410A refrigerant is stored in a pink cylinder.
Manifold gauge sets used with systems charged with
R410A refrigerant must be capable of handling the higher
system operating pressures. The gauges should be rated
for use with pressures of 0−800 on the high side and a low
side of 30" vacuum to 250 psi with dampened speed to 500
psi. Gauge hoses must be rated for use at up to 800 psi of
pressure with a 4000 psi burst rating.
IMPORTANT
Mineral oils are not compatible with R410A. If oil
must be added, it must be a polyol ester oil.
E−Refrigerant Charge and Check
WARNING−Do not exceed nameplate charge under any
condition.
This unit is factory charged and should require no further
adjustment. If the system requires additional refrigerant,
reclaim the charge, evacuate the system, and add required
nameplate charge.
NOTE − System charging is not recommended below 60°F
(15°C). In temperatures below 60°F (15°C) , the charge
must be weighed into the system.
If weighing facilities are not available, or to check the
charge, use the following procedure:
1− Attach gauge manifolds and operate unit in cooling
mode with economizer disabled until system stabilizes
(approximately five minutes). Make sure all outdoor air
dampers are closed.
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