Isc Board - Sequence Of Operation - Carrier WeatherExpert 50LC 07 Series Installation Instructions Manual

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)
capable of three cooling stages. After initial power to the
board, a Green LED will blink with a 1 second duty cycle indi-
cating 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 configu-
ration will indicate the type of error the board has identified.
See Fig. 43 for LED locations and Table 4 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
compressors 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 Conden-
sate Flow Switch can be wired to the COFS Terminal by re-
moving 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 mini-
mum position.
Cooling
In the Cooling Mode, the small and large compressors will be
sequenced to maintain the thermostat temperature setpoint. The
table below shows the cooling operation based on the follow-
ing conditions.
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.
INPUT
Compressor
Thermostat
C1
First Stage
On
Cooling (Y1)
Second Stage
Off
Cooling (Y2)
Third Stage
On
Cooling (Y3)
Humidi-MiZer System (Optional)
®
In the Dehumidification Mode, both compressors will run and
Indoor airflow will be rise to High Speed.
At subcooler reheating mode (reheat-1), during part load con-
ditions 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 Out-
door 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
OUTPUT
Indoor Outdoor
Compressor
Fan Fan
C2
Speed Speed
Low
Off Low
(700 rpm)
Medium
On Medium
(800 rpm)
High
On High
(1000 rpm)
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,
the system outdoor fan will operate as shown in the table below
based on size.
LC SIZE RPM
07 250
Economizer (Optional)
When the economizer is in Free Cooling Mode and a demand
for cooling exists (Y1 on the thermostat), the economizer will
modulate 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 demand for cooling, the out-
door-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 regard-
less of the cooling demand.
If the increase in cooling capacity causes the mixed-air tem-
perature 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 re-
turns to normal once the mixed-air temperature rises above
48°F (9°C). The power exhaust fans will be energized and de-
energized, if installed, as the outdoor-air damper opens and
closes.
In field-installed accessory CO
mizer, 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
proportionally. As the CO
crease of 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 operate at minimum position. Otherwise, the damp-
er 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 outdoor fans will run in the standard cooling mode. If the
Outdoor Fan Select Switch (see Fig. 44) 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 outdoor fans will run in the Minimum Fan Speed
Mode (MIN) set to 160 rpm regardless of the cooling demand.
50LC Size 07 units have a SPST normally open Low Ambient
Switch wired across the TS and OF terminal and a jumper
placed across the PS terminal (see Fig. 45). When the LAS is
active, the switch will close making contact to the OF terminal.
This is done for units that require all outdoor fans to run at the
same pre-set factory Low Ambient Speed.
27
NUMBER OF NUMBER OF
FANS ON FANS OFF
2
sensors connected to the econo-
2
level decreases because of the in-
2
0
set-
2