5566217-JIM-C-1019
36 Johnson Controls Ducted Systems
prevent an unstable signal due to air turbulence, make sure that
there are 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).
Factory-installed VFD
The factory-installed VFD is mounted in the blower access
compartment. The drive comes wired from the factory to include
both 3-phase power and control connections (run permit signal,
speed reference signal, and fault signal). All required drive
parameters are pre-programmed at the factory, except in the
case of 208-volt applications.
For 208-volt applications, you must change the following
parameters.
• Change the parameter that defines the motor nameplate
voltage to a value of 208.00
• Change th parameter that defines motor-rated current to
the appropriate value available on the motor's nameplate.
Refer to the enclosed drive material for instructions on
changing parameter settings.
For units also equipped with gas/electric heat, a terminal block
located in the unit's control box and connected to the VAV
board's VAV BOX terminal, must be field wired to the building's
VAV boxes to ensure fully open dampers during heating
operation.
Manual bypass
An optional, factory-installed manual bypass switch is available
with factory-installed VFD. The manual bypass switch is located
in the blower motor access compartment. The manual bypass
has the following three positions:
• Drive - routes power through the VFD for modulating
control of the indoor blower motor.
• Line (or bypass) - routes power directly to the motor that
provides full-speed motor operation and complete
electrical isolation of the drive.
• Test - routes power to the VFD but not to the motor to
allow for drive programming and diagnostics.
If a drive failure occurs, the unit does not automatically switch to
bypass mode. You must set the line/drive/test to the Line
(bypass) position. If there is a call for the fan, the indoor blower
motor will run at full-speed while in the bypass mode.
BAS-ready VFD
Factory-installed VFD is also available with BAS-ready models.
Terminal blocks are provided in the control box for field wiring of
a customer-installed BAS to receive 24 VAC power and to
connect to the following control signals:
• a duct static pressure transducer input signal (0-5 VDC)
• an economizer actuator input signal (2-10 VDC)
• an economizer actuator output signal (2-10 VDC)
• a VFD speed reference output signal (2-10 VDC)
The use of shielded cable is recommended for the above
control wiring connections.
NOTE: Factory-installed VFD is not available with factory-
installed BAS options due to space limitations in the
control box.
A solid-state, lock-out relay (LR) and 100 microfarad, 50 VDC
capacitor must be field-supplied and installed to provide a
means to transmit a potential fault signal back to the BAS
controller. The specific relay part number required will depend
upon the need for either AC-output or DC-output.
Once the appropriate relay and capacitor are obtained, install
the capacitor across LR terminals 3 and 4 and make the
following wiring connections:
• LR '1' to BAS controller
• LR '2' to BAS controller
• LR '3' to UCB 'X'
• LR '4' to UCB 'C'
VFD-ready for customer installation
Units configured as VFD-ready provide provisions for a
customer-installed drive. The physical dimensions of VFDs can
vary greatly among manufacturers, horsepower ratings, and
voltage requirements. Keep in mind that drive manufacturers
Do not run plastic tubing in the supply or return air ducts
as air movement could cause erroneous pressure
measurements. If the tubing penetrates through the
bottom of the unit, be sure openings are sealed to
prevent air and water leakage.
If the unit is operated with the manual bypass switch in
the Line (bypass) position and there are VAV boxes
present in the duct system, then boxes must be driven to
the full-open position using a customer-supplied power
source to prevent over-pressurizing and possible
damage to the ductwork.
Before you begin any service, disconnect all power to
the drive. Be aware that high voltages are present in the
drive even after power is disconnected. Allow the
capacitors within the drive to discharge before you begin
service.
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