SOLID STATE ECONOMIZER SYSTEM
63-2484—03 18
1
Standard economizer position based on enthalpy control set on the A setting and 50% relative humidity.
2
Closed position is either the minimum position or fully closed, depending on the job setting.
3
Opening/closing is dependent on the mixed air temperature.
OPERATION: W7212
The purpose of the economizer is to use outdoor air for
cooling, whenever possible, to reduce compressor operation.
Power at the N terminal determines the Occupied/Unoccupied
setting:
— W7212A:
• 24 Vac (Occupied).
• No power (Unoccupied).
— W7212C:
• 24 Vac (Occupied).
• No power (Unoccupied).
• Returns to minimum position on failure of CO
2
sensor.
— W7213,W7214:
• W7213 (CHANGEOVER TERMINAL B)
—24V power to B: System is in heating mode.
—No power to B: System is in cooling mode.
• W7214 (CHANGEOVER TERMINAL O)
—24V power to O: System is in cooling mode.
—No power to O: System is in heating mode.
NOTE: When module is operating in Occupied mode, the
minimum position is defined by the potentiometer.
When the module is operating in Unoccupied mode,
and there is no call for cooling, the damper drives
fully closed.
When wired as shown in Fig. 31– Fig. 36, the logic module
responds to the cooling thermostat signal. The system uses
C7400A (or C7400C with W7212C) Solid State Enthalpy
Changeover Sensor(s) or C7660 Dry Bulb Temperature
Sensor. The C7400 responds to both dry bulb temperature
and humidity, allowing use of outdoor air at higher
temperatures for free cooling when humidity is low. The
C7660 responds only to dry bulb temperature; use only in dry,
arid climates and in single dry bulb changeover. Do not use
C7660 for differential dry bulb. If differential control is required,
use enthalpy (C7400).
The logic module functions as a true first stage of cooling
providing maximum energy economy during the cooling cycle.
It automatically locks out free cooling during heating; holding
the outdoor air damper at the minimum position setting.
The logic module can operate as either a basic free cooling
controller, or it can incorporate additional functions. Table 5
details the input/output (I/O) logic of the module.
Fig. 26. S963B1128 Remote Potentiometer used with logic
module for remote damper control.
Table 4. Outdoor air damper positions.
Outside
Temperature
1
Standard Economizer Damper Position
Return
Temperature
1
Differential Enthalpy Damper Position
Modulating
2
3-Position
2
Modulating
2,3
3-Position
2,3
80 Closed Closed 80 Closed Closed
85 Open Open
75 Closed Closed 75 Closed Closed
80 Open Open
70 Open Open 75 Open Open
65 Open Open
60 Open Open 75 Open Open
55 Open Open 75 Open Open
54 and down Modulating Opening/Closing 75 Modulating Opening/Closing
M20603A
P1
P
ECONOMIZER
R
MINIMUM
POSITION
ADJUSTMENT
W
B
CW
CLOSE
S963B1128 REMOTE
POTENTIOMETER
CW
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