284806-YIM-A-0107
18
Unitary Products Group
•
For a single enthalpy operation carefully turn the
set point adjusting screw (found on the damper
control module) to the "A", "B", "C" or "D" setting
corresponding to the lettered curve of the Enthalpy
Setpoint Adjustment Figure 9.
•
For a dual enthalpy operation, carefully turn the set
point adjusting screw fully clockwise past the "D"
setting.
POWER EXHAUST DAMPER SETPOINT (WITH OR WITH-
OUT POWER EXHAUST)
•
With no power exhaust option, adjust the Exhaust
Air Adjustment Screw fully clockwise. This will
allow 2nd stage cooling to operate.
•
With power exhaust option, each building pressur-
ization requirement will be different. The point at
which the power exhaust comes on is determined
by the economizer damper position (Percent
Open). The Exhaust Air Adjustment Screw should
be set at the Percent Open of the economizer
damper at which the power exhaust is needed. It
can be set from 0 to 100% damper open.
INDOOR AIR QUALITY AQ
Indoor Air quality (indoor sensor input): Terminal AQ
accepts a +2 to +10 Vdc signal with respect to the
(AQ1) terminal. When the signal is below it's setpoint,
the actuator is allowed to modulate normally in accor-
dance with the enthalpy and mixed air sensor inputs.
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
2
Space Sensor Kit Part #
2AQ04700324
•
Optional CO
2
Unit Sensor Kit Part # 2AQ04700424
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 requir-
ing 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) pres-
sure in the supply air duct and convert this pressure
measurement to a proportional 0-5 VDC electrical out-
put.
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
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).
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 internal Proportional-Integral (PI) control loop
which continuously calculates an output value.
A brief description of the VAV board's I/O terminals that
are used follows;
•
DUCT PRES
- a 0-5 VDC analog input received
from the duct static pressure transducer.
•
FAN
- a 2-10 VDC analog output sent to the VFD to
control the speed of the indoor blower motor.
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.
