284816-BIM-B-0707
46
Unitary Products Group
NO OUTDOOR AIR OPTIONS
When the thermostat calls for the first stage of cooling,
the low-voltage control circuit from "R" to "Y1" and "G"
is completed. For first stage cooling, compressor #1,
condenser fan motor #1, and condenser fan motor #2
(if the ambient temperature is above 60ºF), is ener-
gized. After completing the specified fan on delay for
cooling, the UCB will energize the blower motor.
When the thermostat calls for the second stage of cool-
ing, the low-voltage control circuit from "R" to "Y2" is
completed. Compressor #2, condenser fan motor #3,
and condenser fan motor #4 (if the ambient tempera-
ture is above 60ºF), is energized, provided it has not
been locked-out.
If there is an initial call for both stages of cooling, the
UCB will delay energizing compressor #2 by 30 sec-
onds in order to avoid a power in rush.
Once the thermostat has been satisfied, it will de-ener-
gize Y1 and Y2. If the compressors have satisfied their
minimum run times, the compressors and condenser
fans are de-energized. Otherwise, the unit operates
each cooling system until the minimum run times for
the compressors have been completed. Upon the final
compressor de-energizing, the blower is stopped fol-
lowing the elapse of the fan off delay for cooling.
To be available, a compressor must not be locked-out
due to a high or low-pressure switch or freezestat trip
and the anti-short cycle delay (ASCD) must have
elapsed.
ECONOMIZER WITH SINGLE ENTHALPY SENSOR -
When the room thermostat calls for "first-stage" cooling,
the low voltage control circuit from "R" to "G" and "Y1" is
completed. The UCB energizes the blower motor (if the
fan switch on the room thermostat is set in the "AUTO"
position) and drives the economizer dampers from fully
closed to their minimum position. If the enthalpy of the
outdoor air is below the setpoint of the enthalpy control-
ler (previously determined), "Y1" energizes the econo-
mizer. The dampers will modulate to maintain a constant
supply air temperature as monitored by the discharge air
sensor. If the outdoor air enthalpy is above the setpoint,
"Y1" energizes compressor #1, condenser fan motor #1,
and condenser fan motor #2 (if the ambient temperature
is above 60°F).
When the thermostat calls for "second-stage" cooling,
the low voltage control circuit from "R" to "Y2" is com-
pleted. The UCB energizes the first available compres-
sor If the enthalpy of the outdoor air is below the
setpoint of the enthalpy controller (i.e. first stage has
energized the economizer), "Y2" will energize com-
pressor #1. If the outdoor air is above the setpoint, "Y2"
will energize compressor #2.
Once the thermostat has been satisfied, it will de-ener-
gize Y1 and Y2. If the compressors have satisfied their
minimum run times, the compressors and condenser
fans are de-energized. Otherwise, the unit operates
each cooling system until the minimum run times for
the compressors have been completed. Upon the final
compressor de-energizing, the blower is stopped fol-
lowing the elapse of the fan off delay for cooling, and
the economizer damper goes to the closed position. If
the unit is in continues fan operation the economizer
damper goes to the min. position.
ECONOMIZER WITH DUAL ENTHALPY SENSORS
The operation with the dual enthalpy sensors is identi-
cal to the single sensor except that a second enthalpy
sensor is mounted in the return air. This return air sen-
sor allows the economizer to choose between outdoor
air and return air, whichever has the lowest enthalpy
value, to provide maximum operating efficiency.
ECONOMIZER (SINGLE OR DUAL ENTHALPY) WITH
POWER EXHAUST
This system operates as specified above with one
addition. The power exhaust motor is energized 45
seconds after the actuator position exceeds the
exhaust fan setpoint on the economizer control. When
the power exhaust is operating, the second stage of
mechanical cooling will not operate. As always, the "R"
to "G" connection provides minimum position but does
not provide power exhaust operation.
ECONOMIZER WITH OPTIONAL VAV OR
INTELLI-COMFORT™ CONTROL
The position of the outside air and return air dampers
are controlled through a 2-10 VDC signal from the VAV
or Intelli-Comfort™ control board. The economizer is
enabled only in Occupied or Recovery mode. When the
control is not powered or is in Unoccupied mode, the
If the unit is operated with the manual bypass
switch in the LINE (BYPASS) position and
there are VAV boxes present in the duct sys-
tem, then boxes must be driven to the full-open
position using a customer-supplied power
source to prevent over-pressurizing and possi-
ble damage to the ductwork.