284806-YIM-A-0107
Unitary Products Group
19
•
VAV BOX
(gas/electric heat only) - a binary output
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 PC software available at
www.yorkupg.com.
FACTORY-INSTALLED VFD
The factory-installed VFD is mounted in the Blower
Access Compartment above the blower assembly. The
drive comes wired from the factory to include both 3-
phase power and control connections (run permit sig-
nal, speed reference signal & fault signal).
All required drive parameters are pre-programmed at
the factory, except in the case of 208-volt applications,
where Parameter 50.16 (which defines motor name-
plate voltage) must be changed to a value of 208.00.
See the enclosed drive user manual for instruction on
changing parameter settings.
For units also equipped with gas/electric heat, a nor-
mally-open, SPST relay located in the unit control box
must be field wired to the building's VAV boxes to
ensure a fully open damper 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 follow-
ing three positions:
•
DRIVE
- routes power through the VFD for modu-
lating 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 diag-
nostics.
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.
BAS-READY VFD
Factory-installed VFD is also available with 'BAS-
ready' models. Terminal blocks are provided in the con-
trol box (in place of the VAV control board) for field wir-
ing of a customer-installed BAS to receive 24 VAC
power and to connect to the following control signals:
The customer must be aware of the duct pres-
sure design limit, and what the duct pressure
sensor is reading when the peak pressure is
reached (ie the pressure transducer sensing
tube may not be located at the place of highest
pressure in the system).
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.
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.
