York ZF150 Installation Manual page 35

call for Differential Demand Ventilation mode for units
installed with economizer option.
• APS - a 24 VAC binary input provided by a field-installed
air proving switch which monitors the pressure difference
across the indoor blower.
• PUR - a 24 VAC binary input for building purge calls from
an external source.
• OCC - a 24 VAC binary input used to set the building
occupancy status for the control.
• LIMIT 2 - a 24 VAC binary input which either confirms
2nd-stage gas heat operation or receives an error signal
from the variable frequency drive.
Outputs:
• FAN - a 2-10 VDC analog output signal sent to the VFD to
modulate the speed of the indoor blower motor.
• ECON - a 2-10 VDC analog output signal sent to the
economizer actuator to modulate position of the return air
and outdoor air dampers (optional).
• EXH ~ - a 24 VAC binary output signal used to turn on/off
the power exhaust relay (optional).
• VAV BOX (gas/electric heat only) - a normally open
relay contact connected to a terminal block, used to drive
the building's VAV boxes to full-open during heating
operation.
Programmable set points:
The duct static set point is the pressure that the drive will
maintain when operating the unit in VAV mode. The set-point is
adjustable between 0" WC and 5" WC with the default setting of
1.5" WC.
The duct static high-limit set point is the maximum allowable
duct pressure to prevent damage from over-pressurization of
the ductwork in the event of either a drive or damper failure.
The high-limit set-point is adjustable between 0" WC and 5" WC
with the factory default setting of 4.5" WC. If the duct static
pressure reaches the high-limit set point, then the supply fan
motor will be shutdown.
NOTE: Either of the set points described above can be
changed through the unit control board (UCB) with the
use of a USB-to-RS485 converter, personal computer
or PDA and a down-loaded copy of the Simplicity®
software available at the UPGnet Commercial Product
Catalog website.
The customer must be aware of the duct pressure
design limit, and what the duct pressure sensor is
reading when the peak pressure is reached (i.e. the
pressure transducer sensing tube may not be located at
the place of highest pressure in the system).
Johnson Controls Unitary Products
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 & fault signal). All required drive
parameters are pre-programmed at the factory, except in the
case of 208-volt applications, in which the parameter that
defines motor nameplate voltage must be changed to a value of
208.00 and the parameter that defines motor-rated current must
be changed to the appropriate value appearing on the motor's
nameplate. Refer to the enclosed drive material or access the
UPGnet Commercial Product Catalog website 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 available
with factory-installed VFD can be found in the Blower Motor
Access compartment and 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
which 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/or diagnostics.
If a drive failure occurs, the unit does not automatically switch to
bypass mode. The LINE/DRIVE/TEST switch must be manually
switched 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.
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 beginning any service, disconnect all power to
the drive. Be aware that high voltages are present in the
drive even after power has been disconnected.
Capacitors within the drive must be allowed to discharge
before beginning service.
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