SOLID STATE ECONOMIZER SYSTEM
63-2484—1
15
Discharge Air Temperature Setpoint
Adjustment—M7415 Only
This temperature range can be adjusted either up or down by
wiring a resistor in series (to increase the setpoint) or in parallel
(to decrease the setpoint) with the C7150B, depending on the
application. See Fig. 18 and 19 for explanation.
T
USE 1%, 1/8 W OR HIGHER RESISTOR
M1544C
T1
M7415
C7150
R
RESISTOR VALUE (OHMS)
681
2760
3650
4420
4750
4870
NO RESISTOR
C7150B SETPOINT °F (°C)
54.5—61.5 (12.5—16.4)
68.4—80.1 (20.3—26.8)
87.4—110.3 (30.8—45.5)
104.7—150 (40.4—65.5)
116—194 (46.7—90)
120—300 (49—149)
50—56 (10—13.3)
Fig. 18. Increasing C7150B setpoint.
T
USE 1%, 1/8 W OR HIGHER RESISTOR
M1545C
T1
M7415
C7150
R
RESISTOR VALUE (OHMS)
18.2K
24K
30K
NO RESISTOR
C7150B SETPOINT °F (°C)
36—44 (2.2—6.7)
39.5—47 (4.0—8.3)
42—49 (5.6—9.4)
50—56 (10—13.3)
Fig. 19. Decreasing C7150B setpoint.
W7459A,C,D Solid State Economizer Logic
Module
Two potentiometers with screwdriver slots for adjustment are
located on the face of the module.
Minimum Position Adjustment
W7459A,D Economizer Logic Module
쐃 Make sure the factory-installed jumper is in place
across terminals P and P1 (terminals T and T1 are
disconnected.
쐇 Connect 24 Vac at terminals TR and TR1 and adjust
the potentiometer on the face of the W7459A,D with a
screwdriver for desired minimum position.
W7459C Economizer Logic Module
쐃 Connect 24 Vac at terminals TR and X (D is not
connected).
쐇 Adjust thumbwheel on motor for desired minimum
position.
Enthalpy Changeover Setpoint
Single enthalpy: the enthalpy changeover setpoint is set to
return the outdoor air damper to the minimum position when
the enthalpy rises above its setpoint. The enthalpy setpoint
scale markings, located on the W7459, are A, B, C, D; see
Fig. 15 for the corresponding control point. The factory-
installed 620-ohm jumper must be in place across terminals +
and S
R.
Differential Enthalpy Changeover Setting
(Use this option only with two-stage cooling
thermostats.)
Differential enthalpy control uses two C7400 Enthalpy
Sensors or two C7650A Temperature Sensors connected to
one W7459 Solid State Economizer Logic Module.
The setpoint scale markings, located on the W7459, are
A,B,C, and D. Turn the setpoint potentiometer fully clockwise
to the D setting. The economizer selects the air that has lower
enthalpy or temperature for cooling; for example, if outdoor
air has lower enthalpy or temperature than return air, the
outdoor air damper is opened to bring in outdoor air for free
cooling.
IMPORTANT
Do not use C7650A Solid State Temperature
Sensors with W7459D high enthalpy limit devices.
SEQUENCE OF OPERATION
Economizer Sequence of Operation
(With and Without Differential Enthalpy)
The economizer operating sequence for both the modulating
and the three-position control systems are identical when the
outdoor enthalpy temperature is above the mixed air setpoint
of 55°F (13°C). The operating sequence for both, using a
standard two-stage thermostat is:
쐃 The first stage of the thermostat signals a need for
cooling.
쐇 The W7459 Solid State Economizer Logic Module
begins to make decisions regarding the unit/
economizer operation.
쐋 a. On the standard (non-differential) economizers,
the logic module checks the outdoor air C7400
Enthalpy Sensor or C7650 Temperature Sensor
to determine if the enthalpy or temperature is
below the setpoint.
b. On the differential economizers, the logic module
checks to determine if the outdoor air
temperature is below the return air temperature.
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