56
AGR 070A through 100A
Product Manual AGR-3
F.
Control System: A centrally located weatherproof control panel shall contain the
field power connection points, control interlock terminals, and control system. Power
and starting components shall include factory fusing of fan motors and control circuit;
control transformer, individual contactors for each fan motor, solid-state start timer,
solid-state three-phase motor overload protection, inherent fan motor overload
protection and unit power terminal blocks for connection to remote disconnect switch.
Terminals shall also be provided for power supply to the evaporator heater circuit.
Hinged access doors shall be lockable. Barrier panels are required to protect against
accidental contact with line voltage when accessing the control system. The
operating and equipment protection controls shall be:
Global UNT microprocessor based control that accomplishes unit capacity control by
6-stage cross-circuit compressor cycling based on leaving chilled water temperature.
The sensor shall be field wired and mounted in thermowells factory installed in the
evaporator water nozzles. Set point and control band shall be easily field adjusted
and anti-cycling and stage delay relays are to be included. Equipment protection
controls shall include low and high refrigerant pressure cutouts, low evaporator flow,
sensor failures, and evaporator freeze protection. Motor protection shall include
phase voltage, volts ratio, and solid state compressor motor protection. The
controller shall be equipped with a Zone Terminal option that provides an onboard
LCD display of unit operating parameters and adjustment of any optional controls.
- OR -
MicroTech microprocessor control with a 12 key keypad and 4-line, 40 character
backlit liquid crystal display operator interface. The controller shall continuously
perform self-diagnostic checks on all system temperatures, pressures, and equipment
protection controls, and automatically shut down a circuit or the entire unit at fault
conditions. The cause, time, and date of the occurrence shall be recorded and
displayed along with availability to view the seven previous incidents.
The controller shall take proactive measures to stay on-line for non-critical
abnormalities; staging down capacity, activating a pre-alarm signal and automatically
switching to the alarm menu on the display. These pre-alarms shall be self-clearing
when the off-condition is corrected.
Critical shutdown alarms such as high condenser pressure, freeze protection, and low
evaporator pressure shall be manual reset and cleared at the keypad to resume
operation.
The refrigerant discharge pressure shall be controlled by a FanTrol system cycling
condenser fans based on discharge pressure and shall be operational 40
°
F (4.4
°
C).
- OR -
The refrigerant discharge pressure shall be controlled by a SpeedTrol control
employing both fan cycling and fan speed control and allow operation to
0
°
F (-18
°
C).