SOLID STATE ECONOMIZER SYSTEM
63-2484—1
16
쐏 a. On the standard economizers, the damper motor
is energized if the outside air temperature is
below the enthalpy setpoint, thereby opening the
damper and introducing outside air to cool the
conditioned space.
b. On differential economizers, the damper motor is
energized if the outside air temperature is below
the return air temperature, thereby introducing
outside air to cool the conditioned space.
쐄 If the logic module uses the outside air for cooling, the
mixed air sensor prevents the entering air from going
below 55°F (13°C).
a. On the modulating system, the control closes the
outside air damper and opens the return air
damper to mix the outside air and return air to
maintain 55°F (13°C).
b. On the three-position system, the mixed air
sensor switch opens, closing the fresh air damper
until the mixed air sensor temperature returns
above 55°F (13°C), closing the switch and
opening the outside air damper.
쐂 a. If the logic module senses that the outside air is
not suitable for cooling, the air conditioning unit
compressor is energized and the space is cooled
with refrigerated air.
b. On the two-stage thermostat, the economizer is
the first stage if the outside air temperature is
suitable for cooling. The compressor on the unit
is energized if the second stage of the
thermostat is energized, thereby creating an
integrated economizer.
쐆 Refer to Table 4 for further information on outside air
damper positions.
쐊 The W7459D has a high enthalpy limit and defaults to
mechanical cooling when the outdoor enthalpy reaches
the preset limit. Do not use a dry-bulb sensor for a high
temperature limit. Refer to Table 5 for further
information on outdoor air damper positions.
Standard Economizer Damper Position Differential Enthalpy Damper Position
Outside
Temperature
1
Modulating
2
3-Position
2
Return
Temperature
1
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
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.
Table 4. Outdoor air damper positions.
Table 5. W7459D maximum outdoor enthalpy switching.
Free Cooling Mode Switching
Outdoor
RH
(Percent)
Into Free Cooling
(LED ON) on
Decreasing Outdoor
Enthalpy
Out of Free Cooling
(LED OFF)
onIncreasing
Outdoor Enthalpy
25 83° ±0.5°F 85° ±0.5°F
50 78° ±0.5°F 80° ±0.5°F
60 76° ±0.5°F 78° ±0.5°F
75 73° ±0.5°F 75° ±0.5°F
CHECKOUT AND TROUBLESHOOTING
Tables 6 through 9 provide step-by-step economizer
checkout and troubleshooting steps. See Fig. 19 and 20 for
enthalpy setpoint potentiometer, minimum position
potentiometer and LED and meter locations.
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