IM 613 / Page 8 (Rev. 7/99)
Sensor Diagnostics
If a temperature sensor’s value is out of range, the UVC will
detect it and take the appropriate action. Each sensor fault has a
specific priority, alarm indication, and set of response actions.
Actuator Feedback Diagnostics
The UVC will monitor the position feedback voltages of every
modulating actuator provided with a particular unit ventilator. If a
feedback value is out of range, the UVC will detect it and
discontinue control of that actuator. Each feedback failure fault
has a specific priority and alarm indication.
Brownout Protection
The brownout feature is meant to protect the compressor and
electric heat contactors from low voltage or “brownout” condi-
tions. If the supply voltage to the unit ventilator is below 85% of
the nameplate value, the UVC will detect it, indicate it, and
de-energize the compressor and electric heaters.
High Pressure
If excessive pressure in the refrigeration circuit is detected by the
external pressure switch, the compressor will be de-energized
immediately (hardware wired). The UVC will immediately
de-energize the reversing valve, disable the compressor and
indicate the alarm.
Low Coil Temperature
External thermostats will sense the DX and water coil
temperatures (if present). The UVC will monitor each thermostat,
and if a low coil temperature is detected, alarm indication and
the appropriate action will occur.
Low Refrigerant Temperature (Water Coil)
If the WSHP unit is in the heating mode and the refrigerant
temperature is too low, the UVC will indicate the alarm and
immediately de-energize the compressor and reversing valve.
Communication Error (Master/Slave Units Only)
If a communication error occurs between a slave UVC and its
master, the alarm will be indicated at the slave, and the affected
units will continue operating. For further information, refer to the
description of the master/slave communication type in the
“Factory Configured Options” section of this manual.
Change Filter (Network Units Only)
When the unit ventilator fan run-time exceeds a network-
adjustable setpoint, a change filter alarm is indicated locally and
over the MicroTech network.
The master controller establishes the following parameters for
itself and for each of its slaves:
• Operating mode (occupied, unoccupied, or tenant override)
• Minimum OA damper position setpoint
• Occupied heating and cooling setpoints
• Unoccupied heating and cooling setpoints
Because each UVC in the zone uses its own room
temperature sensor and a common room temperature setpoint,
even temperature control will be maintained regardless of any
load variation within the zone.
Master: A master UVC is similar to stand-alone UVC. The only
difference is that Comm B of a master controller is used for
master/slave network communications. The minimum position
setpoint, room setpoint, unoccupied offset, operating mode, and
remote setpoint adjustment (if used) must be set at the master.
Slave: A slave UVC receives its operating mode and the above
setpoint information from its master. When communications are
established between a slave and its master, the slave will ignore
its three on-board setpoint potentiometers.
Communication Failure: If the communication link between a
slave and its master fails, the slave UVC will indicate the alarm
and continue to operate using the temperature and minimum
position setpoints defined by its on-board potentiometers. Its
operating mode will be that last received from its master, or if
power is cycled, it will default to occupied.
MicroTech Network
A variety of MicroTech unit and auxiliary controllers can be
interconnected to form a MicroTech network. A MicroTech
network provides a building operator with the capability to perform
advanced equipment control and monitoring from a central or
remote location. A network UVC is a controller that has been
programmed with the software required to operate in a Micro-
Tech network. The following features are provided for each
network UVC over the MicroTech network:
In addition to the various heating and cooling options, the
AAF-HermanNelson product line provides several factory-
configured options that affect installation requirements and unit
control. These options are either factory programmed, factory
wired, or both. The model number code string specifies which
options are present in a particular unit ventilator. The following
options are described in this section:
• Communication type (stand-alone, master/slave or network)
• ASHRAE cycle II
• Room temperature sensor (unit or wall mounted)
• Tenant override (unit or wall mounted)
• Remote room setpoint adjustment
• Day-night changeover
• Ventilation lockout
• Exhaust fan interlock
Communication Type
All Unit Ventilator Controllers can be programmed to operate in
one of the following communication modes:
• Stand-alone
• Master/slave
• MicroTech network
Stand-alone
A stand-alone UVC does not communicate over a network. It is
independent and capable of performing complete room
temperature and ventilation control.
Master/Slave
The master/slave application is designed to provide even
temperature control of a zone containing up to six unit
ventilators. One controller in the zone must be designated and
programmed to be the master, and up to five controllers may be
designated and programmed to be its slaves.
Factory Configured Options
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