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349215-JIM-B-1008
When the AQ signal exceeds it's setpoint setting and
there is no call for free cooling, the actuator is propor-
tionately modulated from the 2 to 10 Vdc signal, with 2
Vdc corresponding to full closed and 10 Vdc corre-
sponding to full open. When there is no call for free
cooling, the damper position is limited by the IAQ Max
damper position setting. When the signal exceeds it's
setpoint (Demand Control Ventilation Setpoint) setting
and there is a call for free cooling, the actuator modu-
lates from the minimum position to the full open posi-
tion based on the highest call from either the mixed air
sensor input or the AQ voltage input.
•
Optional CO
Space Sensor Kit Part #
2
2AQ04700224
•
Optional CO
Sensor Kit Part # 2AQ04700124
2
Replace the economizer access panel.
OPTIONAL BAS-READY ECONOMIZER POWER
EXHAUST DAMPER SET POINT ADJUSTMENT
Remove the economizer access panel from the unit.
Loosen, but do not remove the two panel latches.
Locate the economizer actuator, where the following
adjustment can be made.
With power exhaust option, each building pressuriza-
tion requirement will be different. The point at which the
power exhaust comes on is determined by the econo-
mizer's outdoor damper position. The actuator's auxil-
iary switch adjustment screw should be set at the
damper position at which the power exhaust is needed.
The adjustment screw can be set between 25 to 85
degrees open.
Replace the economizer access panel.
OPTIONAL VARIABLE AIR VOLUME (VAV)
A variable air volume (VAV) option using a variable fre-
quency drive (VFD) is available for applications requiring
a constant supply duct static pressure. A differential
pressure transducer is used to monitor supply duct static
pressure and return a speed reference signal to the VFD
to control the output of the indoor blower motor.
DUCT STATIC PRESSURE TRANSDUCER
A 0-5" WC pressure transducer, located in the control box
compartment, is used to sense static (gauge) pressure in
the supply air duct and convert this pressure measure-
ment to a proportional 0-5 VDC electrical output.
Pressure-transmitting plastic tubing (1/4" diameter)
must be field supplied and installed from the transducer
to both the ductwork and to the atmosphere. Connect
18
the tubing from the 'HIGH' pressure tap of the trans-
ducer to a static pressure tap (field supplied) in the
supply duct located at a point where constant pressure
is expected. To prevent an unstable signal due to air
turbulence, there should be no obstructions, turns or
VAV terminal boxes up- or down-stream of the sensing
tube location for at least a distance of 6-10 times the
duct diameter. Tubing must also be run between the
'LOW' pressure tap of the transducer and atmospheric
pressure (outside of the unit).
Do not run plastic tubing in the supply or return
air ducts as air movement could cause errone-
ous pressure measurements. If the tubing pen-
etrates through the bottom of the unit be sure
openings are sealed to prevent air and water
leakage.
VAV CONTROL BOARD
A VAV control board, located in the top-left corner of
the control box, is used to convert the pressure trans-
ducer input signal into a speed reference signal that
the drive uses to control the speed of the blower motor.
This modulating speed reference signal is generated
using an algorithm which continuously calculates an
output value.
A brief description of the VAV board's I/O terminals that
are used follows:
Inputs:
•
DUCT PRES - a 0-5 VDC analog input provided by
a factory-installed duct static pressure transducer
located in the unit's control box.
•
SAT - analog input provided by a factory-installed
10k-ohm, type 3 thermistor located in the unit's
supply air compartment.
•
RAT - analog input provided by a factory-installed
10k-ohm, type 3 thermistor located in the unit's
return air compartment.
•
OAT - analog input provided by a factory-installed
10k-ohm, type 3 thermistor located in the outdoor air
compartment or mounted within the evaporator base
rail for units without the installed economizer option.
•
ST - analog input provided by field-installed space
temperature sensor.
•
OH - a 0-10 VDC analog input provided by a field-
installed outdoor air relative humidity sensor for
single enthalpy economizer configuration.
Johnson Controls Unitary Products
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