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40
LOW TEMPERATURE COMPRESSOR LOCKOUT
SWITCH—The Economizer is equipped with a low ambient
temperature lockoutswitchlocated in the outdoorairstream whichis
used to lock out the compressors below a 42_F(5.6_C) ambient
temperature.
Economizer Contro l Modes
—Determine the Economizer control
mode before set up of thecontrol. Some modes of operation may
require different sensors. Refer to Table 11. The Economizer is
supplied from the factory with a supply air temperature sensor, a
low temperature compressor lockout switch, and an outdoor air
temperature sensor. This allows for operation of the Economizer
with outdoor air dry bulb changeovercontrol. Additional
accessories can be added to allow for different types of changeover
control and operation of the Economizer and unit.
OUTDOOR DRY BULB CHANGEOVER— The standard
controllerisshippedfromthefactoryconfiguredforoutdoordrybulb
changeover control. The outdoor air and supply air temperature
sensors are included as standard.
For this control mode, the outdoor temperature is compared to a
selectable set point on the sensor. See Fig. 39. If the outdoor--air
temperature is above the set point, the Economizer will adjust the
outdoor air dampers to minimum position. If the outdoor--air
temperature is below the set point, the position of the outdoor--air
dampers will be controlled to provide free cooling using outdoor
air. When in this mode, the LED next to the free cooling set point
potentiometer will be on. The changeover temperature set point is
set using the switches on the sensor. See Fig. 39 for the
corresponding temperature changeover values.
In this mode of operation, the outdoor--air temperature is compared
to the return--air temperature and the lower temperature airstream is
used forcooling. When using this mode of changeover control, turn
the free cooling/enthalpy set point potentiometer fully clockwise to
the D setting. See Fig. 38 and Fig. 43.
EXHAUST FAN
SETPOINT
LED LIGHTS WHEN
EXHAUST CONTACT
IS MADE
MINIMUM DAMPER
POSITION SETTING
MAXIMUM DAMPER DEMAND
CONTROL VENTILATION
SETPOINT
LED LIGHTS WHEN
DEMAND CONTROL
VENTILATION INPUT
IS ABOVE SETPOINT
DEMAND CONTROL
VENTILATION SETPOINT
LED LIGHTS WHEN
OUTDOOR AIR IS
SUITABLE FOR FREE
COOLING
ENTHALPY
CHANGEOVER SETPOINT
A09708
Fig. 38 -- Economizer Controller Potentiometer and LED
Locations
(8.9°C)
(11.7°C)
(12.8°C)
(14.4°C)
(17.2°C)
(20°C)
(22.8°C)
(25.6°C)
A10134
Fig. 39 -- Outdoor Air Temperature Changeover Set Points
RETURN DUCT
(FIELD-PROVIDED)
RETURN AIR
SENSOR
ECONOMIZER
A09710
Fig. 40 -- Enthalpy Sensor Mounting Location
604D-- --A