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ISC BOARD - SEQUENCE OF OPERATION
General
The Carrier Integrated Staging Control (ISC) is intended for use
with a standard thermostat or direct digital controls (DDC) capa-
ble of three cooling stages. After initial power to the board, a
Green LED will blink with a 1 second duty cycle indicating the
unit is running properly. In the event of the ISC board failing, the
Green LED will be OFF or continuously ON. When the unit is not
running properly, the Green LED will blink along with Red LED
lights. The Red LED light configuration will indicate the type of
error the board has identified. See Fig. 55 for LED locations and
Table 8 for a list of status codes.
The ISC board can be remotely shutdown by removing Jumper 4
and wiring to the Remote Shutdown terminal. The Smoke Control
Module can shutdown the unit by removing Jumper 3 and wiring
to the Smoke Shutdown terminal. The Smoke Alarm terminal on
the ISC Board provides a pass through connection should a smoke
alarm signal be connected. In the case of the RTU Open option,
the RTU Open controller provides the signal which is passed
through the ISC board to the Smoke Alarm terminal.
The crankcase heater will run at all times, except when the com-
pressors are running. An auxiliary power supply (24 vac) available
at TB-4 Terminal is provided to power auxiliary equipment. An
optional Phase Monitor Relay can be wired to the PMR terminal
by removing Jumper 5. An optional Condensate Flow Switch can
be wired to the COFS Terminal by removing Jumper 7.
Ventilation
In the Ventilation/Fan Mode (G on the thermostat), the indoor fan
will run at low speed and the damper will operate at minimum
position.
Cooling
In the Cooling Mode, the small and large compressors will be se-
quenced to maintain the thermostat temperature setpoint. The
chart below shows the cooling operation based on the following
conditions.
INPUT
Compressor
Thermostat
C1
First Stage
On
Cooling (Y1)
Second Stage
Off
Cooling (Y2)
Third Stage
On
Cooling (Y3)
The outdoor fan and VFD controlled indoor-fan will operate at
low, medium and high speed. The RPM is factory set by the CFM
and static pressure requirements for the unit installed.
Humidi-MiZer
System (Optional)
®
In the Dehumidification Mode, both compressors will run and In-
door airflow will be rise to High Speed.
At subcooler reheating mode (reheat-1), during part load condi-
tions when the room temperature and humidity are above the set
point, the unit initiates the sub-cooling mode of operation; a call
for cooling and dehumidification. RDV (Reheat Discharge Valve)
and TWV (Three Way Valve) close; Indoor and Outdoor airflow
will rise until reaching 100% of Speed.
At hot-gas-bypass reheating mode (reheat-2), when there is a call
for dehumidification without a call for cooling, a portion of the hot
gas from the compressor bypasses the condenser coil when RDV
opens and hot gas is fed into the liquid line, TWV closes in this
mode and the system provides mainly latent cooling. Indoor air-
flow will rise until reaching 100% of Speed, Outdoor airflow will
run at High speed as long as outdoor temperature is above 80°F
(26.7°C); when operating in this mode below 80°F (26.7°C) OAT,
All manuals and user guides at all-guides.com
OUTPUT
Indoor
Outdoor
Compressor
Fan
Fan
C2
Speed
Speed
Low
Off
Low
(700 rpm)
Medium
On
Medium
(800 rpm)
High
On
High
(1000 rpm)
the system outdoor fan will operate as shown in the table below
based on size.
48LC SIZE
RPM
08
160
09
160
12
160
Economizer (Optional)
When the economizer is in Free Cooling Mode and a demand for
cooling exists (Y1 on the thermostat), the economizer will modu-
late the outdoor-air damper to provide a 50°F (10°C) to 55°F
(13°C) mixed-air temperature into the zone and run the indoor fan
at high speed. As mixed-air temperature fluctuates above 55°F
(13°C) or below 50°F (10°C) dampers will be modulated (open or
close) to bring the mixed-air temperature back within control.
Upon more call for cooling (Y2 on the thermostat), the outdoor-air
damper will maintain its current position, compressor C1 will run
and the outdoor fan will run at low speed. If there is further de-
mand for cooling, the outdoor-air damper will maintain its current
position, compressor C2 will run and the outdoor fan will run at
medium speed. The VFD-controlled indoor fan will operate at
high speed regardless of the cooling demand.
If the increase in cooling capacity causes the mixed-air tempera-
ture to drop below 45°F (7°C), the outdoor-air damper will return
to the minimum position. If the mixed-air temperature continues
to fall, the outdoor-air damper will close. Control returns to nor-
mal once the mixed-air temperature rises above 48°F (9°C). The
power exhaust fans will be energized and de-energized, if in-
stalled, as the outdoor-air damper opens and closes.
If field-installed accessory CO
omizer, a demand controlled ventilation strategy will begin to op-
erate. As the CO
level in the zone increases above the CO
2
point, the minimum position of the damper will be increased pro-
portionally. As the CO
level decreases because of the increase of
2
fresh air, the outdoor-air damper will be proportionally closed. For
economizer operation, there must be a thermostat call for the fan
(G). If the unit is occupied and the fan is on, the damper will oper-
ate at minimum position. Otherwise, the damper will be closed.
Low Ambient Cooling Operation Down to 40°F (4°C)
In Low Ambient RTU conditions when the temperature is be-
tween 55°F (13°C) and 40°F (4°C), the Low Ambient Switch
(LAS) will be active and the outdoor fans will run to the pre-set
factory outdoor fan speed. When the temperature is greater than
65°F (18°C), the Low Ambient Switch will deactivate and the out-
door fans will run in the standard cooling mode. If the Outdoor
Fan Select Switch (see Fig. 56) is in the ON position, the outdoor
fans will run in the Fan Cycle Speed Mode (FCS) set to 250 rpm.
If the Outdoor Fan Select Switch is in the OFF position, the out-
door fans will run in the Minimum Fan Speed Mode (MIN) set to
160 rpm regardless of the cooling demand.
LC Size 08 through 12 units have a SPDT Low Ambient Switch
wired to the OF terminal and the Outdoor Fan Relay (see Fig. 57).
The jumper across the PS terminal will be removed. When the
LAS is active, the switch will close making contact to the OF ter-
minal and will drop connection to the ODF Relay. When electrical
connection is removed from the ODF Relay, the PS connection
will be opened. This will place the third outdoor fan electrically
isolated from receiving any speed command, which will then turn
the motor off. This is done for units that only require two outdoor
fans to run at the same factory pre-set Low Ambient Speed.
33
NUMBER OF
NUMBER OF
FANS ON
FANS OFF
2
1
2
1
2
1
sensors are connected to the Econ-
2
set-
2
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