Page 40
B−Outdoor Air Dampers (240/288 units)
Dampers are manually operated to allow up to 25 percent
outside air into the system at all times.
C−Economizer (all units)
(Factory Installed)
The optional economizer used on SCA240/SCB288 and
SCA120 units can be used with downflow and horizontal
air discharge applications. The economizer uses outdoor
air for free cooling when temperature and/or humidity is
suitable. An economizer hood is required and must be or-
dered separately.
NOTE − Gravity exhaust dampers are required with power
exhaust.
The economizer is controlled by the economizer control
module A56 which connects to the main control module
A55. Both boards are part of the Integrated Modular Control
(IMC) which controls unit operation.
The economizer will operate in one of two modes. Each
mode requires a different EM1 economizer DIP switch set-
ting. Each mode also requires different sensors.
1−TMP" MODE (SENSIBLE TEMPERATURE)
In the TMP" mode, the IMC uses input from the factory
installed RT6 Supply Air Sensor, RT16 Return Air Sensor, and
RT17 Outdoor Air Sensor to determine suitability of outside air
and economizer damper operation. When outdoor sensible
temperature is less than return air sensible temperature, out-
door air is used for cooling. This may be supplemented by me-
chanical cooling to meet comfort demands. This application
does not require additional optional sensors.
2−GLO" MODE (GLOBAL)
Global Mode − The GLO" or global mode is used with an
energy management system which includes a global con-
trol feature. Global control is used when multiple units (in
one location) respond to a single outdoor air sensor. Each
energy management system uses a specific type of out-
door sensor which is installed and wired by the controls
contractor.
NOTE − All economizer modes of operation will mod-
ulate dampers to 55_F (13_C) supply air.
D−Gravity Exhaust Dampers
(all units)
Gravity exhaust dampers must be used any time an econo-
mizer or power exhaust fans are applied to SCA/SCB series
units.
Gravity exhaust dampers allow exhaust air to be discharged
from the system when an economizer and/or power exhaust is
operating. Gravity exhaust dampers also prevent outdoor air
infiltration during unit off cycle. See installation instructions for
more detail.
E−Power Exhaust Fans (all units)
Power exhaust fans are used in downflow applications only.
The fans require optional down-flow gravity exhaust dampers
and economizers. Power exhaust fans provide exhaust air
pressure relief and also run when return air dampers are
closed and supply air blowers are operating. Figures 24 and
25 show location of the power exhaust fans. See installation
instructions for more detail.
FIGURE 24
SCA120 LAGED & LAPEF
GRAVITY
EXHAUST
HOOD
LAPEF POWER
EXHAUST FAN
ASSEMBLY
LAGED GRAVITY
EXHAUST DAMPERS
FIGURE 25
SCA240/SCB288 LAGED & LAPEF
LAPEF
POWER EXHAUST
FAN ASSEMBLY
LAGED
GRAVITY
EXHAUST
DAMPERS
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