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C-Cooling Start-Up
A-Operation
1 - Initiate first and second stage cooling demands
according to instructions provided with thermostat.
Note - ZGB074 units are equipped with two-stage
compressors.
2 - No Economizer Installed in Unit -
A first-stage cooling demand (Y1) will energize com-
pressor 1 and the condenser fan. An increased cooling
demand (Y2) will not change operation.
Units Equipped With Economizer -
When outdoor air is acceptable, a first-stage cooling
demand (Y1) will energize the economizer. An in-
creased cooling demand (Y2) will energize compres-
sor 1 and the condenser fan. When outdoor air is not
acceptable unit will operate as though no economizer
is installed.
074 Units With No Economizer Installed-
A first-stage cooling demand (Y1) will energize com-
pressor on low speed (67% capacity) and the condens-
er fan. An increased cooling demand (Y2) will energize
the compressor to high speed (full capacity)
074 Units Equipped With Economizer -
When outdoor air is acceptable, a first-stage cooling de-
mand (Y1) will energize the economizer. An increased
cooling demand (Y2) will energize compressor on low
speed (67% capacity) and the condenser fan. When
outdoor air is not acceptable unit will operate as though
no economizer is installed.
3 - Units contain one refrigerant circuit or stage.
4 - Unit is charged with R-410A refrigerant. See unit
rating plate for correct amount of charge.
5 - Refer to Refrigerant Charge and Check section for
proper method to check refrigerant charge.
B-Three Phase Scroll Compressor Voltage Phasing
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 follows: 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 K1 contactor. 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-Safety or Emergency Shutdown
Turn off power to unit. Close manual and main gas valves.
IV-CHARGING
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 re-
quired 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:
IMPORTANT - Charge unit in standard cooling mode
high stage only.
1 - Make sure outdoor coil is clean. Attach gauge
manifolds and operate unit at full CFM in cooling
mode with economizer disabled until system
stabilizes (approximately five minutes). Make sure
all outdoor air dampers are closed.
2 - Compare the normal operating pressures (see
tables 8 - 11) to the pressures obtained from
the gauges. Check unit components if there are
significant differences.
3 - Measure the outdoor ambient temperature and
the suction pressure. Refer to the appropriate
circuit charging curve to determine a target liquid
temperature.
Note - Pressures are listed for sea level applications.
4 - Use the same thermometer to accurately measure
the liquid temperature (in the outdoor section).
•
If measured liquid temperature is higher than the
target liquid temperature, add refrigerant to the sys-
tem.
•
If measured liquid temperature is lower than the
target liquid temperature, recover some refrigerant
from the system.
5 - Add or remove charge in increments. Allow the
system to stabilize each time refrigerant is added
or removed.
6 - Continue the process until measured liquid
temperature
temperature. Do not go below the target liquid
temperature when adjusting charge. Note that
suction pressure can change as charge is adjusted.
7 - Example ZGB036: At 95°F outdoor ambient and a
measured suction pressure of 130psig, the target
liquid temperature is 102°F. For a measured liquid
temperature of 106°F, add charge in increments
until measured liquid temperature agrees with the
target liquid temperature.
Page 37
agrees
with
the
target
liquid
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