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SGH/SCH036, 060, 120, 240
Cooling Start-Up
WARNING
Electric shock hazard. Can cause injury
or death. Before attempting to perform
any service or maintenance, turn the
electrical power to unit OFF at
disconnect switch(es). Unit may have
multiple power supplies.
IMPORTANT-The crankcase heater must be energized for
24 hours before attempting to start compressor. Set
thermostat so there is no demand to prevent compressors
from cycling. Apply power to unit.
MSAV
TM
Units and Units Equipped With Voltage or
Phase Detection
- The Unit Controller checks the incoming
power during start-up. If the voltage or phase is incorrect,
the Unit Controller will display an alarm and the unit will not
start.
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
according to instructions provided with thermostat.
Refer to the Optional Supply Air VFD section on
MSAV
t
units.
2- SG/SC 036 & 060 Units—First-stage thermostat
demand (Y1) will energize the compressor and blower
on low speed along with the condenser fan. An
increased cooling demand (Y2) will increase the blower
and compressor to high speed. On units with an
economizer, when outdoor air is acceptable, a
first-stage demand (Y1) will energize the economizer.
An increased demand (Y2) will energize the
compressor and blower on low speed along with the
condenser fan.
SG/SC 120 Units
—First-stage thermostat demand will
energize compressor 1. Second-stage thermostat
demand will energize compressor 2. On units with an
economizer, when outdoor air is acceptable, a
first-stage demand will energize the economizer; a
second-stage demand will energize compressor 1.
SG/SC 240 Units—
First-stage thermostat demand will
energize compressors 1 and 2. Second-stage
thermostat demand will energize compressors 3 and 4.
On units with an economizer, when outdoor air is
acceptable, a first-stage demand will energize the
economizer; a second-stage demand will energize
compressors 1 and 2.
IMPORTANT
Three Phase Scroll Compressor Voltage Phas
ing
Three phase scroll compressors must be phased sequen
tially to ensure correct compressor and blower* rotation
and operation. Compressor and blower are wired in
phase at the factory. Power wires are color-coded as fol
lows: line 1-red, line 2-yellow, line 3-blue.
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 field-installed wires connected to the
line side of S48 disconnect or TB13 terminal strip. 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.
*Supply air VFD motors should rotate in the correct di
rection; verify scroll compressor rotation separately.
Contact technical support if the VFD blower is rotating
incorrectly. The blower rotation will always be correct on
MSAV
TM
units (120/240 units will always have VFD mo
tors). Checking blower rotation is not a valid method of
determining voltage phasing for incoming power.
3- SG/SC 120 units contain two refrigerant circuits and
two stages of cooling. See figure 27.
4- SG/SC 240 units contain four refrigerant circuits or
systems. Evaporator and condenser coil refrigerant
circuits 1 and 2 make up stage 1 cooling in thermostat
mode. Evaporator and condenser refrigerant circuits 3
and 4 make up stage 2 cooling in thermostat mode. See
figure 28.
