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installed on Pins 1 & 2), Normal Mode (Jumper installed
on Pins 2 & 3) and Comfort Mode (Jumper Removed).
The factory default position is the Efficiency Mode. The
Efficiency mode has a variable suction pressure setpoint
that will vary with the outdoor temperature; as the outdoor
temperature increases the suction pressure setpoint will
decrease. When the Operation Mode jumper is installed
in the "Normal Mode" the suction pressure setpoint is 135
psig. When the Operation Mode jumper is installed in the
"Comfort Mode" the suction pressure setpoint is 125 psig.
Unit Operation
4SCU23LX Unit Operation with a Comfort Sync
A3 Communicating Thermostat
When the 4SCU23LX unit is installed with a Comfort Sync
A3 Communicating Thermostat and Comfort Sync-enabled
indoor unit, the unit capacity will be controlled in the
variable capacity mode throughout the range of capacity
from minimum capacity to maximum capacity based upon
thermostat demand in cooling mode. The indoor air volume
will be controlled to match compressor capacity throughout
the capacity range.
4SCU23LX Unit Operation with a Conventional
24VAC Non-Communicating 2-Stage Thermostat
When the 4SCU23LX unit is installed with a conventional
24VAC non-communicating 2-stage thermostat, a Y1 first
stage cooling demand will initiate cooling operation and
first stage indoor blower operation. The compressor will
be controlled in the variable capacity mode by varying the
compressor capacity to obtain the target suction pressure
set point. The Y2 second stage cooling demand will initiate
second stage blower operation. Increased air volume
will increase the load on the indoor coil and increase the
suction pressure. The 4SCU23LX compressor capacity will
continue to be controlled based upon the suction pressure.
The unit capacity will be controlled in the variable capacity
mode throughout the range of capacity from minimum
capacity to maximum capacity. If the Y2 demand remains
after 20 minutes, the 4SCU23LX control will begin to
ramp up the compressor capacity until maximum capacity
is achieved. The 4SCU23LX unit will cycle off once the
thermostat demand is satisfied.
4SCU23LX Unit Operation with a Conventional
24VAC Non-Communicating Single-Stage
Thermostat
When the 4SCU23LX unit is installed with a conventional
24VAC non-communicating single-stage thermostat, a Y1
first stage cooling demand will initiate cooling operation and
cooling indoor blower operation. In single stage thermostat
applications, a jumper must be installed between Y1 and
Y2 on the 4SCU23LX outdoor control. The compressor
will be controlled in the variable capacity mode by varying
the compressor capacity to obtain the target suction
Page 20 of 25
pressure set point. If the cooling demand remains after 20
minutes, the 4SCU23LX control will begin to ramp up the
compressor capacity until maximum capacity is achieved.
The 4SCU23LX unit will cycle off once the thermostat
demand is satisfied.
Start-Up
If unit is equipped with a crankcase heater, it should
be energized 24 hours before unit start-up to prevent
compressor damage as a result of slugging.
1.
Rotate fan to check for frozen bearings or binding.
2.
Inspect all factory and field-installed wiring for loose
connections.
3.
After evacuation is complete, open liquid line and
suction line service valves to release refrigerant
charge (contained in outdoor unit) into system.
4.
Replace the stem caps and secure finger tight, then
tighten an additional 1/6 of a turn.
5.
Check voltage supply at the disconnect switch. The
voltage must be within the range listed on the unit
nameplate. If not, do not start equipment until the
power company has been consulted and the voltage
condition corrected.
6.
Connect manifold gauge set for testing and charging.
7.
Set the thermostat for a cooling demand. Turn on
power to the indoor indoor unit and close the outdoor
unit disconnect switch to start the unit.
8.
Recheck voltage while the unit is running. Power must
be within range shown on the unit nameplate.
9.
Check system for sufficient refrigerant using the
procedures outlined under Checking Refrigerant
Charge.
Operating Manifold Gauge Set and Service
Valves
The liquid and vapor line service valves are used for
removing refrigerant, flushing, leak testing, evacuating,
checking charge and charging. Each valve is equipped
with a service port which has a factory-installed valve
stem. Figure 14 and Figure 15 provide information on how
to access and operate both ball- and angle-type service
valves.
Torque Requirements
When servicing or repairing ventilating and air conditioning
components, ensure the fasteners are appropriately
tightened. Table 8 lists torque values for fasteners.
Issue 2231
CAUTION
508296-01
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