Carrier WeatherExpert 50LC 07 Series Service And Maintenance Instructions page 27

ISC BOARD - SEQUENCE OF OPERATION
General
The Carrier Integrated Staging Control (ISC) is intended for use
with a standard thermostat or direct digital control (DDC) capable
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 run-
ning 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. 39 for LED locations and
Table 5 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 (24Vac) 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 mini-
mum position.
Cooling
In the Cooling Mode, the small and large compressors will be se-
quenced to maintain the thermostat temperature setpoint. Table 6
shows the cooling operation based on the following 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.
Table 6 — Cooling Operation
INPUT
Compressor
Thermostat
C1
First Stage
On
Cooling (Y1)
Second Stage
Off
Cooling (Y2)
Third Stage
On
Cooling (Y3)
Economizer (Optional)
When the economizer is in Free Cooling Mode and a demand for
cooling exist (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 55ºF
(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.
OUTPUT
Indoor Outdoor
Compressor
Fan Fan
C2
Speed Speed
Low
Off Low
(700 rpm)
Medium
On Medium
(800 rpm)
High
On High
(1000 rpm)
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
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. 40) is in the up 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 down position, the out-
door fans will run in the Minimum Fan Speed Mode (MIN) set to
160 rpm regardless of the cooling demand.
The 50LC**07 units have an SPST normally open Low Ambient
Switch wired across the TS and OF terminal and a jumper placed
across the PS terminal (see Fig. 41). 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 fac-
tory Low Ambient Speed.
Fig. 40 — Outdoor Fan Speed Select Switch
PS
TS
Fig. 41 — Schematic of SPST Low Ambient Switch
Table 7 shows the operation of the outdoor fan for size 07-12
units.
27
sensors are connected to the econ-
2
level decreases because of the increase of
OF SPEED
SELECT
ON
FCS
MIN
OFF
JUMPER ON
PS
OF
LAS
SPST
set-
2